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Has kin selection enabled the evolution of interspecial communication?
I know animals often imitate specific behaviour (like when they show their teeth to evoke "danger!" in the reciever) as a form of communication. Although, for a fully-fledged language where we can express anything we can think of to develop, we need more complicated signals.
And for that, we need both the reciever and the signaler to understand the same signalling system. And since for a language as complex, the animals need to share a lot of similar "associations" with similar signals - it's good when the communicating animals orientate a similar environment - such as siblings.
Is this a possible explanation of the evolution of language?
I know the signalling theory is a biological branch on its own, however I seem not to be able to come up with an alternative explanation. Also, I know that this kind of group selection is sometimes used to explain the evolution of altruism. So is this how the evolution of communication happens?

Perhaps better asked on Linguistics.SE?

@anongoodnurse If my hypothesis is true, it applies on all kinds of complex communication systems.

@anongoodnurse Also I was mindblown when I realized that this had to be minimally the way altruism has evolved.

I don't know about this.  I manage to communicate fairly well with my dogs and horses, and they with me.

@jamesqf They've learned that if they'll respond in certain wain on certain stimuli, they'll got some reward. The problem occurs when we notice that the relationships among animals don't often work that way. Similar ideas are discussed in the book The evolution of language

@Probably: But they've also learned that if they direct certain stimuli to me, I will (generally) respond in certain ways, which will get them what they want. That's certainly communication, isn't it?

@jamesqf I think it's the same case - they learn certain behavior to get rewards. But when you signal to your collegue an information about a bear standing behind him, it's an "altruistic" behavior because when the bear isn't after you specifically, you got some time to run while the bear is chewing your collegue. And, of course, it turns out not to be altruistic considering everyone would have done that in your situation. But this situation occurs only if someone goes first with to "try" if altruism pays of - and of course, since he's the only one, his DNA won't be passed on.

So for altruistic behaviour you need the population to evolve this mutation at the same time. And evolution of such trait within a family seemed like a nice explanaiton for me, even though there are certainly ways to avoid that - if the animals interact in the means of the theory of games, they could have evolved altruistic genes as well.

@Probably: Well, all of language is just behavior learned to get rewards (or to avoid punishment).  As for altruism, your example (like most supposed altruism) is really just an example of forward thinking.  That is, by warning the colleague, you trade a small risk that the bear will catch you instead of him for the large potential benefit that he may provide you in the future.

@jamesqf Sure, my point was that being the "first altruist" doesn't pay of. Of course, everything we do is driven by endorphines but it's a different kind of reward system when there's not just stimulus-reflex behaviour

You're probably right to say that, neurologically speaking, there's no difference between the "rationally learned" and "stimulus-reflex" behaviour   (even though some consider the border to be The theory of mind). The difference important for our case is that it doesn't pay to be the "first altruist" but it pays for your horses to listen to you (and that's not even a "rationally learned" behavior btw since they're domesticated)

You're probably right to say that, neurologically speaking, there's no difference between the "rationally learned" and "stimulus-reflex" behaviour   (even though some consider the border to be The theory of mind). The difference important for our case is that it doesn't pay to be the "first altruist" but it pays for your horses to listen to you (and that's not even a "rationally learned" behavior btw since they're domesticated)

@Probably: But it often does pay to be the first altruist, as long as you don't invest too much in the altruistic act.  Further, I'm not sure that I buy into the idea that there's a difference in kind between "stimulus-response" and "rationally learned".  And endorphins are a result, not a cause, though of course they can establish a feedback cycle.

@jamesqf Well, apart from establishing a feedback cycle, I had on mind the neurotransmiters neurons use in a similar way to navigate new paths as well. But about the difference between "stimulus-response" and "rationally learned": you're right, phisiologucally, it's just about the level of complexity of communication but your horses are domesticated so there might be an evolutionary predisposition to listen to you - basically all behavior in smaller mamalls is driven by evolution.

The selective pressure towards cooperation can occur only once they've got an advantage when they start cooperating. Otherwise, you would have to assume group selection for altruistic behavior, which is not accepted among biologists.

@Probably We are starting a Bioacoustics Stack Exchange for people interested in the studies of non-human animal sounds and the impacts of sounds on animals. Please join us! https://area51.stackexchange.com/proposals/126698/bioacoustics?referrer=YjZmYjUxYzJkNDI1YmY5NDk3NzdhMzViMmZlNzI4ZDdiYTAyMWQxNTM5ZWFiNzRhODNkMmFiMzIxZjI3MmY1N_gFvrICTvBsmYNJ2ptRM6lIZEAV-VGkXtIwNyVDja680


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Does parental conflict lead to genes combining important functions with functions only advantageous for one of the parents?
In a sitation of a mother-father conflict of interests, the mother might use epigenetics to turn off some genes only advantageous for the father's genes and not her own. I thought a logical father's contra-strategy would be to bind the functions only advantageous to him to some of the genes crucial for them both, so that the mother couldn't turn these genes off.
Is there any evidence for a similar mechanism of "taking some genes hostage" in a situation of a conflict of interests?

While epigenetics is something the mother organism may control to some extent, I don't see how the father could do anything of the sort. Binding genes together requires genetic changes that take many generations, i.e., "father" in this case is not an organism but indication of the way the gene was transmitted.

@Vadim I broadened my question to any parent because I imagined it could be the case if the father's genes affected the chances of the fetus being miscarried.

It sounds like this question is asking about imprinting. However, you don't specifically mention that term so perhaps you are unaware of the research on this subject? If so, there was a relevant review published last year in PLOS Genetics. A "Learn Genetics" page and  "journal club" article in Nature could also be of interest.

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What kind of people are more likely to catch COVID-19?
It is well known that people of old age or with respiratory problems are more vulnerable by the effects of COVID-19. However, I wasn't able to find information on any similar trends on catching the disease in the first place.
So what are the factors predicting the most significant differences in the chance of catching COVID-19?
I'm looking for predictors of the immune system response, whether that would be smoking, age or gender, not obvious notions such as "people from populated areas".
I know the role of ethnicity is much debated but since there's no conclusive evidenence yet, I'm not interested in its role.

Evidence suggests higher death rates from COVID-19 including
among racialised groups might be linked to higher levels of a cell
surface receptor molecule known as ACE2. But this can result from
taking drugs for diabetes and hypertension, which takes us back to the
point about the social causes of such diseases. (The Conversation)

might be worth looking at this for starters. I imagine that occupation is likely one of the biggest predictors of catching covid-19 - https://www.ons.gov.uk/employmentandlabourmarket/peopleinwork/employmentandemployeetypes/articles/whichoccupationshavethehighestpotentialexposuretothecoronaviruscovid19/2020-05-11

@AlexReynolds Can you make this into a full answer?

@AlexReynolds I'm looking for biological, not behavioral determinants.

There are populations that might be more vulnerable due to genetics surrounding the ACE2 receptor. For instance, men are more likely than women to get severe cases of COVID-19:

A growing body of evidence reveals that male sex is a risk factor for a more severe disease, including death. Indeed, globally, ~60% of deaths from COVID-19 are reported in men7,8, and a recent cohort study of 17 million adults in England reported a strong correlation between male sex and risk of death from COVID-19 (hazard ratio 1.99, 95% confidence interval 1.88-2.10)8

The ACE2 gene lies on the X chromosome. In addition to polymorphisms distributed by ethnicity, women have two X chromosomes and may gain some protection from differences in their two alleles of the ACE2 gene, which could make viral binding more difficult, or alter the signaling pathways which result in the subsequent autoimmune response that damages internal organs:

In addition to differential polymorphisms which may explain susceptibility and even outcome in different ethnic populations, the fact that ACE2 is localized to Xp22.2 may help explain the observed male-associated risk. As such, even in the absence of variation in this gene, the monoallelic versus biallelic presence of this gene may impact the natural history and prognosis of COVID-19 in males.

Additionally, in some ethnic populations, expression of the ACE2 gene (as measured by mRNA levels) is lower in women than in men, which may account for reduced infectivity or disease severity in women:

In the normal human lung, ACE2 is expressed on type I and II alveolar epithelial cells. Among them, 83% of the type II alveolar cells have ACE2 expression. Men had a higher ACE2 level in their alveolar cells than women. Asians have a higher level of ACE2 expression in their alveolar cells than the White and African American populations. The binding of SARS‐CoV‐2 on ACE2 causes an elevated expression of ACE2, which can lead to damages on alveolar cells. Damages to alveolar cells can, in turn, trigger a series of systemic reactions and even death.

This aspect of research seems to be ongoing. Region-specific behavior does seem to be the main driver for new infections, however: Ignoring public health guidelines and reopening economies early, calling the virus a hoax, giving healthcare workers garbage bags for PPE, etc. etc. Biology takes a backseat, when governments deliberately put people in harm's way.

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Why is hunting big animals more dangerous for the species?
I've heard in a lecture about protection of primates that one reason the classical population dynamics doesn't work is that the aboriginal hunters tend to hunt the big, strong and healthy individuals that have the best chance of becoming a successful parent.
Is this effect really so significant that it outweighs the fact that the hunters don't have to hunt so many of them in order to get the same amount of meat?
[Additional explanation]:
This question asks about the best strategy in protecting rare wild animal species against excessive hunting. We don't have to intervene when lions hunt zebras because less zebras means less food for lions - so the ratio of zebras and lions doesn't change much so there's no danger of any species getting extinct. Unlike the natural predators and prey, it has been found that the amount of meet hunted by people in forests isn't anyhow dependant on the number of animals living in the nature because humans use tools which give them a huge advantage over the "prey". Also, number of people living in a forest isn't  dependent on the sources in the wild, due to the rise of agriculture.
There was a research how much is the size of an animal connected to the probability a hunter will hunt specifically this animal and it has been found that the hunters tend to pick the physically biggest, strongest and healthiest individuals. This phenomenon has been marked as dangerous for the future preservation of wild species because (that's my guess) the most healthy and strong are the most likely to rear healthy offspring. I said to myself that from what I've learned about evolution, the difference between the physical fitness of an individual feed by a less strong parent (compared to the rest of the population) and an individual feed by a stronger parent can't be so big that it overweighs the fact that when a hunter hunts smaller animals, he's more likely to hunt more of them (That's something that has been studied) so the overall number of hunted animals is actually bigger. So my question is, wheter I'm correct or wheter the factor of the bigger number of animals you hunt when you hunt small animals actually isn't as important as the fact that healthy and strong parents will rear healthy and strong offspring.

@Hallur I edited the question to make it clearer. Yes, the animals are endangered by the hunters who kill them.

keep in mind primates take a long time to reproduce and reach maturity, many times when you kill a parent you are also killing living but not fully grown offspring, and for many primates it can also destabilize the society as well, which hurts everyone and can cause more subsequent deaths. The largest healthiest primate tend to also be the highest standing in the trope, so killing them can trigger infighting and infanticide.

@John Oh yes, the nutritional differences can definitely play a role. It just seems to me that when you kill an animal before its reproductive age, you affect the nature much more.

Size is not the same thing as as age, primates can vary quite a bit in size and health independent of age. the biggest in not automatically the oldest. in an interdependent social species the rank of the individual has other effects. think of it like the difference between the president dying and a homeless guy dying while both are regrettable one has a much stronger effect on the rest of the population.

@John Hmm...I guess the assumption that the size doesn't say much about the age is too general to be the case. But you have a point, the stronger individuals should be better at providing nutrients for the others.

This question still doesn't make any sense. I can't understand what you're asking at all - can you frame your question in a single, easy-to-understand, grammatically-correct sentence? Are you asking about how humans affect the evolution of primates? Which ones? Or are you asking about the effects of killing a prime figure in a family unit on the offspring? Please clarify exactly what kind of situation you are asking about, and what your question actually is. Some citations supporting the ideas presented in your question as facts would also be useful.

I can see two different sides to this question.
On one side,
From Darwin's Theory of Evolution, the more adapted you are, the better chance at reproducing you will have, thus passing on your genes.

"Survival of the fittest" is a phrase that originated from Darwinian
  evolutionary theory as a way of describing the mechanism of natural
  selection. The biological concept of fitness is defined as
  reproductive success.

In this case, you hunt the fittest, strongest animals that can procreate and protect their descendants, leaving the weakest alive. The weakest may not be able to continue the lineage because of their weakest gene pool and the species existence could be at stake.
On the other side,
A reputated Oxford Zoologist, Richard Dawkins wrote:

We are survival machines – robot vehicles blindly programmed to
  preserve the selfish molecules known as genes

In this particular example, being strong, fit and healthy could be interpreted as being unfit for evolution, since it attracts predators (humans) to kill, as would not be the case for medium sized less meaty healthy individuals. The true adaptation that could make the specie survive in this case is via the weakest members that are not worth the effort to be hunted but still can survive other threats.
There is several more viewpoints that could be described knowing more details about exactly which animals, their environnement, the other predators and the exact contribution of the "healthy strongest" specimens you described as being hunted.
Nevertheless, hunting animals can always endanger the specie depending on the frequency of the hunt, frequency of the animal reproduction and several other factors, so can many other human behaviors.
Source: The selfish gene - Richard Dawkins (Book)

Sorry, you got it wrong. When I wrote that it is dangerous for the species when the hunters hunt the stronger individuals more often, I didn't mean it could cause troubles due to the selective pressure, I meant that when a parent is healthy and strong, it probably doesn't lack nutrients himself, so it can't fully concentrate its effort towards providing food for the offspring. Also there is a better chance the offspring will even born and grow up healthy.

@Probably"when a parent is healthy and strong, it probably doesn't lack nutrients himself, so it can't fully concentrate its effort towards providing food for the offspring"  This makes no sense. Your comment is as clear as your question was before Hallur's edit...

@Probably I answered the question "Why is hunting big animals more dangerous for the species?". Evolution has it's say in this because it will truly determine the degree at which hunting the big animals affects the survival of the specie (i.e the "dangerouseness for the specie"). Take it as an answer in the long time, this can be discussed a lot since it isn't a specific scenario that can be studied but rather a general question.

It was my edit and I'm not talking about evolutionary disadvantage, I'm talking about disadvantage in physical fitness (yes, it is being passed on from parent to offspring as well to a certain extent.)

@Probably I think you are misunderstanding the lecture you heard. If the lecturer was talking about fitness, they almost certainly meant it in an evolutionary context. If you hunt the strongest animals, you are culling those who have been most successful in their environment. Leaving behind only the evolutionarily weaker animals means that the next generation may be weaker as well. Smaller animals could also be young/not sexually mature, so you reduce a population's rate of reproduction by taking out the animals that would otherwise have the best chance to reproduce successfully.

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Is the human eye supposed to see the lense effect?
Just as the GoPro cameras, we need lenses to be able to focus. Nevertheless, we can see the "fisheye effect" on the shots taken by GoPros. I am talking about this:

Is it possible to notice the "fish eye effect"? Or does the brain somehow eliminate this distortion?
[EDIT:]
My insufficient knowledge of optics tells me that, as we have lenses in our eyes, we should see the worlds through a thicker layer of mass in the middle of our field of vision, and through a thinner layer of mass on the margins of our field of vision. We know that our vision is reversed when it enters the eye. Is it inflated in the middle as well?
Is there any "distortion" in the proportions of different parts of the image (that is filtered-out at brain), or the does the image formed in retina have the proportions of different parts same as the actual scene?

Human eyes do not have the same optical properties as fish-eye lenses. As should be plain from your everyday experiences using your sense of vision, we do not see a fish-eye effect.

@MattDMo ...because the brain "filters" this effect out?

Why would the effect be there in the first place?

@AliceD Because we watch the world through lenses and there is a thinner layer of glass in the middle than on the margins.

@WYSIWYG Could you please move this question to Cognitive science?

@MattDMo We also don't see our "blind spot," nor do we see the world upside down.  It's also hard to notice depth of field.  But we know all these things must exist because our eyes are physical optical systems.  The OP's question is a good one to ask, and I'd also like to know how the distortion (which is guaranteed to exist) gets filtered out.

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Why do women mature (physically) earlier than men?
All sources I've read (the first page) states that the fact that women mature (in the sense of physical maturing) earlier than man is caused by the earlier selective prunning in brain. Though, this is an explanation just for the mechanism, not for the cause.
So what is the real evolutionary reason women mature earlier (though, probably slower) than men?

When asking for "evoluitonary reason", always be careful to not fall into the pit of the panselectionist view of evolution (as briefly explained in the second paragraph of this answer). This is just a warning but your question is fine!

What do you mean by "no chance in the concurence"? Otherwise, good question regarding ultimate versus proximate causes.

A quick look at "All sources I've read" suggests that the "maturing" here is entirely psychological, and quite subjective.  (And on a personal note, I've done quite well for some decades now by refusing to either "grow up" or "act my age" :-))

When you say all sources I've read, have you really read all  9,920,000 results? You might want to be more specific about what you read.

What kind of maturing are you asking about? Reproductive (sexual) maturity - the ability to ovulate and carry a pregnancy? Social maturity - acting like a "grown-up", not constantly making jokes centered around the physical elimination of waste, ability to maintain a polite conversation, ability to handle responsibilities and make appropriate decisions? Emotional maturity - the ability to recognize, validate, and control one's emotions in a socially-responsible manner? Physical maturity - achieving one's final height, full development of secondary sex characteristics, full set of teeth, etc.?

How about religious maturity - the ability to fully participate in all rituals and practices of your chosen religion or belief system? My point is, the word "maturity" on its own is vague and misleading. Your question is unclear, and needs to be edited to reflect exactly what you are asking about. You might also want to research a bit more than just glancing at the first page of a single vague Google search.

My guess is that the reproductive age of women is shorter and therefore they invest into the earlier development, unlike men that would have no chance in the concurence of all the men up to 70. This sentence makes absolutely zero sense to me. Please rewrite it in a grammatically correct and informative fashion. We don't have any clue what you're talking about or what point you're trying to get across. If you are having a difficult time expressing yourself in English, get a more fluent colleague, friend, or associate to help you.

@Remi.b The first page

@MattDMo All kinds of "maturities" are tightly bind together, just as I wrote, the mental maturity (religious, personality) is connected with the blood level of the hormones which is the key thing for the reproductive maturity.

@Probably your final paragraph in italics is fundamentally flawed. You seem to think that mating (and reproducing) is a zero-sum game, which it absolutely is not. First, you completely overlook the possibility of multiple partners. Second, your hypothesis that women are somehow automatically attracted to older men is just wrong, if you take 2 seconds to think about it. You block "older men" into a single group, and there's certainly a significant difference between an 18-year-old woman and a 30-year-old man vs. that same woman and a 70-yo man. Also, some women like younger men - just ask them.

@Probably "men don't affect the reproductive fitness of the offspring as much [as women]" Do you have any evidence whatsoever to support that statement? "older men have better chances to succeed between the girls because they're better physically developed" When was the last time you actually looked at an 18-yo standing next to a 50-yo man? Which one is more fit and "physically developed"? How do you know that older people have fewer parasites? It would be just as likely for them to have more, because they've lived longer and accumulated more.

@Probably "men are in principle fertile till death" Umm, no. That's just plain wrong. How many 60- or 70-yo new fathers do you know? "there's no reason of spending resources on the physicall development (maturing) in the age when they have no chance of succeeding between the other men (i.e., before 15 years)" Again, what does this even mean? Of course someone who has not hit puberty doesn't have a chance of "succeeding" because they're not even playing the game! Afterwards, it's pretty much an equal playing field. Male and female adults exist in equal numbers, so all get a chance.

@Probably "All kinds of "maturities" are tightly bind together, just as I wrote, the mental maturity (religious, personality) is connected with the blood level of the hormones which is the key thing for the reproductive maturity." No, I beg to differ. Sexual maturity has nothing to do with emotional or social maturity. Just because you can doesn't mean you should, as the saying goes. There are plenty of teen parents who don't have as much social maturity as my 11-yo son.

@Probably Your entire question is a string of unsupported opinions tenuously connected together to give a completely unreasonable conclusion. You still haven't defined what you mean by "maturity", so it is impossible to know what you're asking about or to give a clear answer. Your "facts" are either misinterpreted or just wrong, and you clearly don't seem to understand evolution very well. I'd suggest taking the brief class Understanding Evolution from the University of California, Berkeley, then delving deeper into some topics.

@MattDMo: WRT 60-70 year old new fathers, you could probably find about as many as have the resources,  financial and otherwise, to attract women of childbearing age - and these days, of course, the desire to become fathers.  And for fitness, I know a number of 50+ individuals who are in far better shape than a lot of 18 year old couch potatos.  There's a lot more individual variation than you seem to think.

@jamesqf I was speaking (well, writing) there in generalities about populations, which is why I didn't bring up individual variation. Yes, of course there can be vast differences between individuals. Perhaps I should have said "average 18-yo vs. an average 50-yo". Women individually also have vastly different preferences for men. My overall point is that the OP has not thought through the question very carefully, and has made a lot of unsubstantiated claims, a number of which are simply incorrect.

@MattDMo Ok, thank you for your corrections. Just one basic thing: You don't a selective pressure to apply universally on the whole population, all you need it is just to be more stronger on individuals with some common trait. Apart from that I didn't mean "older men" as "elderly", I meant "more developed, mature" men.

As I said, of course men aren't fertile literally till death, the important thing is that the age is much longer than women's. Of course not everyone who is physically mature is as well sexually (I assume you mean maturity that consists of the awareness of your sexual identity, otherwise it's physical maturity) and mentally mature. I don't want to offend anyon but clearly, these things usually go along.

I've read it and there's nothing new for me. Please select the individual mistakes if you want to discuss them. I just find it obvious that there's much bigger difference between older women and young women than between young and older men.

@MattDMo: I agree on the lack of thinking through.  As I said earlier, most of the "maturity" seems to be purely subjective.  As for fathers in their 60s, my neighbor - 102 last birthday - has a daughter in her 40s, so it can be done.

@jamesqf I totally agree. Some family friends had an "oops" pregnancy when he was in his late 50s (she's probably 10-15 years younger than him), so it's definitely possible. All I'm saying is that it's rather rare.

@MattDMo: Sure, but I think the rarity is due less to physical inability, than to relatively few older men having the financial resources to attract women of childbearing age.

@MattDMo Ok, I've removed the part what I think, please don't consider it in your potential answer

I'm fine to delete any unfair comments from the list. The question can have two interpretations, it is a bit ambiguous: Why is there a gender difference in the age of maturation, growth and fertility in humans? One interpretation is biochemical reasons, and the other is human ecology and evolutionary reasons. The biochemical ones are subject to evolutionary pressure, as all neoteny is, so i understood the evolutionary pressures as being the driving factor for the reason of the difference. It's a very good quesiton that requires proper phrasing.

The problem with the question is that you refer to an article that talks about mental maturity, and you are instead querying about the entire process of different gender maturation time in males and females. what are the reasons for the earlier growth, physical and mental maturation of human males and females, and illustrate the query with a good summary of the ages males and females get different morphological and mental changes.

The tags you use are not related to the question.

@comprehensible Well all the sources were connecting the fact with the intensity of the selective prunning so I don't know why should it be so crutial to seperate mental and physical maturity but I'm asking primarily about the physical because I understand that such effects can be partially a work of society habits.

This is a question about Neoteny and Heterochrony.
The closest field of study which will have specialists of this kind of topic is the study of the late maturation of humans compared to other species, which has had some research: 5-7 years ago there were some papers measuring the different bone growth rates of humans compared to chimpanzees and exploring the notion of natural selection through preference of immature traits: being attracted to girls with child like faces, smaller nose, large eyes, small voice, babyish, with various causes for example allowing for later brain pruning and longer brain development.
If you research in google publications you can find some research on the topic, for example:
Heterochrony in human evolution: the case for neoteny reconsidered
Sexual selection, physical attractiveness, and facial neoteny: cross-cultural evidence and implications (1995)
The origins of sex differences in human behavior: Evolved dispositions versus social roles.
It's all about evolutionary selection due to survival fitness. A complex age dynamic is at work in human evolution due to our extended lifetime, memory and brain size, amidst heavily variable social patterns (mate selection, monogamy, tribe size, bride rights, patriarchal/matriarchal systems) in paleolithic humans.
Bonobos mature at roughly the same time: 9 years, and female bonobos have a baby at 11 to 13 years. I think that illustrates the flexibility of maturation age according to the role of the adults.
Human females can have babies in between 9 and 15 years for the most part, some of them at 7, so maturation age is an evolutionary trait rapidly changeable according to fitness of the resulting offspring, so it is entirely fine tuned by survival performance.
EDIT: I wrote this answer to be helpful, but apparently my lack of sources and "errors?" deserve a mark down. so here is an additional text:
"They found that Paleolithic girls arrived at menarche - the first occurrence of menstruation - between seven and 13 years. This is a similar age to modern girls, which suggests that this is the evolutionarily determined age of puberty in girls.
'This would have matched the degree of psychosocial maturation necessary to function as an adult in Paleolithic society based on small groups of hunter-gatherers,' they write.
Disease and poor nutrition became more common as humans settled, causing puberty to be delayed. Modern hygiene, nutrition and medicine have allowed the age of menarche to fall to its original range.
However, today there is a mismatch between sexual maturity and psychosocial maturity, with sexual maturity occurring much earlier. This mismatch is a result of society becoming vastly more complex, with psychosocial maturity therefore taking longer to reach."
Note that they are talking about female adult paleolithic maturity and tasks at that age. Females compete for mates by attractiveness and fitness, and some research suggests that males compete for females by other mechanisms, even force or threat.(ref)
There is clearly a reason for which men are available to make and care for their offspring later than females. Females prefer older males by at least a couple of years with moderate adult muscle mass(ref), and in our species males of 17 to 35 years are biologically the strongest and wisest. Nature would have it that 11 /13 year old fathers clearly are counter productive to the survival of their partner and child in an ordinary setting of hunter gatherers, because of the very long gestation and complexity of human survival tasks.
The human mental maturation range has a wide variety of deviation, and between the age of 8 and 25, we are pre-programmed to be in an intense task of learning and physical adventure. Physical coordination of the male can reach an optimal level as late as the age of 22, 3/4 years after his bones have finished growing and his muscles and reflexes have had time to increase and adapt to his new frame, which is why athletes are at their physical peak between the ages of 18-27, and the "mental pruning" article suggests that their mind continues to re-organize itself well beyond the age of 30. During that stage, a human male is programmed to learn a wide array of advanced skills: flint knapping, tool making, botanic knowledge, hunting skills, clothes making, landscape exploration, orientation, memorization of food places, wells, tree climbing, metal work, net weaving, pottery, pigments, weapons, blow darts, wild animal experience (game, lions, rhinos, birds, rodents, traps, stalking, poisons, frogs) etc... All that time based survival experience reinforces the notion that a male reaches his functional optimum as a provider and protector of his family well after his sexual maturation age.
Females have a less physically intensive role to play in human society. While they can learn all the hunting/survival skills of the male, their central role is to be nourished and provide for the child(ref). Their parenting tasks rely less on individual memory because they stay socially at home more (papua new gineans, africans, aborigines, yanomami). Their task can be less intense physically, require less physical training, and can be less intensive on memory and adventure (being nourished, childcare, craftwork, leadership of the group at home and less in exploration and precarious tasks). Both the human male and female memory has a very important role for guiding the group. A female can provide guidance up till the age of 50-90 in a natural setting.
Females are generally less expendable and adventurous than males, because a male can potentially have 3 offspring every day, he is limited by the number of females, and she can only have 1 offspring every 9 months, she is more precious to the multiplication of the group.
Add to that the function of memory, hunter gatherer fitness, and social acumen, absorption of mental and survival skills
Other great apes have gestation periods arount 8.5 months compared to our 9.
Because of the difficulty to assess the paleolithic social and environmental pressures that caused the sex age maturation difference, it's a question that theorists would be unwise to wade into to any great depth, in an academically competetive field. A good anthropologist should be able to list all the predominant selection factors.

This doesn't answer the question, and is really just a bunch of hand-waving without much in the way of supporting citations. "It is well-known that females prefer older males with young adult muscle mass in almost all species" Actually, it isn't. Citation needed. "maturation age is an evolutionary trait entirely tuneable according to fitness of the resulting offspring, so it is entirely fine tuned by survival performance." Again, citation needed. Finally, your last sentence basically says "I read the first results from a Google search and don't actually know what I'm talking about."

Onset of menarche at 9 years old is a very recent phenomenon due to significantly increased environmental exposure to estrogen and its analogs, as well as some other as-yet-unagreed-upon causes. Historically, girls living in 6th to 15th century Europe, for example, began menstruating at an average age of 14.

Finally, your last sentence basically says "I read the first results from a Google search and don't actually know what I'm talking about" ... No it sais your markdown is idiotic. I search science publications for 30 minutes and find that the topic, which is conjectural, has virtually no precedent, I publish here what precedent there is in related fields. I'm not inclined to argue with someone who speaks nonsense and who has no better answer than I do. You are an example of a negative forum contributor with low experience in biological academia. Use established measurements from extant tribes.

They found that Paleolithic girls arrived at menarche - the first occurrence of menstruation - between seven and 13 years. This is a similar age to modern girls, which suggests that this is the evolutionarily determined age of puberty in girls. That's not just one factual accuracy of my text. you may as well consider the entire text as relatively well informed... and learn... because you are not informed, and yet you act as if you were. listen and learn. i'm certainly not a very good biologist in this field but i am effortlessly less misguided than yourself.

Much of the information contained in this post requires additional references. Please [edit] to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted. I don't care if your statements are correct or not, they still need to be supported by peer-reviewed literature. Scientists understand that. I'm not going to address your personal attacks, as they only reflect negatively on yourself. You don't know me, so don't make assumptions.

I never mark down other users except if they provide negative imput to the forum, because i have regard and empathy for their efforts. your first comment contains a flat personal critique, and your second comment contains a falsehood. clearly you are not wise enough to interact with the page, citing false information as you do. I've added references for everything, because i didn't stray into inexperience as you did in you second comment, oxford and cambridge zoology. botany, human sciences, and ecology departments dont provide a narrow base of culture: read a single book on human sciences.


text:
Does urine therapy really work?
I heard a lecture from a supporter of urine therapy and he claimed that urine is not only good disinfection but also as rich source of minerals. To me, these two advice seemed contradictory.
In addition, the supporter emphasized one should use his own urine - and yet, as an example of the magical effect of urine therapy we got a story of a boy who was hooked by jellyfish but was saved by a nearby doctor who used urine of his own. Apart from that I see no reason why urine should work against toxins better than a water or a disinfection (they don't).
Though, I know a very qualified doctor who advocated this treatment. What do you think?

There are people for both for and against in the case of urinating to cure the pain from jellyfish stings. There is no research supporting the claim though.

This is at best anecdotal evidence. First of all, urine is, although it has been thought otherwise for decades, not sterile. The bacteria in it just don't grow under the conditions used in the lab which are used to proof bladder infections. See these two articles:

Evidence of uncultivated bacteria in the adult female bladder.
Urine is not sterile: use of enhanced urine culture techniques to
detect resident bacterial flora in the adult female bladder.

When you take into account that bacteria grow on almost all surfaces which have a connection to the outside (like mouth, stomach, gut and so on) this is not really surprising that this is true for the bladder as well.
Urine might be a relatively low risk solution of choice to rinse a wound when nothing else is available, but otherwise I wouldn't recommend it.
Then think of what urine is used for: it is the way our body excretes all the water soluble stuff it doesn't need any more. The body makes a lot of effort here to concentrate the primary urine in our kidneys to recover all the stuff which is still needed and to save water. I wouldn't drink it and make my body go through the whole process of excretion again.
About the doctors: is there any hard evidence for that or is this only an anecdote? I get highly skeptical when I hear about such stories.


text:
How do we share pain?
When somebody else tells me about his or her itching or pain in some specific body part, I sometimes begin to feel similar feelings.
I can think of about three explanations:

I feel pain all over my body all the time for many different reasons but my entrance neural pathways stop it as unimportant of these signals but when I focus on a single signal, it begins to be important for me.
Mirror neurons are doing their job.
For an unknown reason, I psychosomatically induce my friend's feelings.

Which of these theories is at least partially engaged in said phenomenon?

can't say unless we do an fMRI of you :P

@Probably - this isn't a universal phenomenon, therefore it's unique to the person experiencing it. I would guess that it's a manifestation of suggestive hypervigilance or valetudinarianism.

what about situation when male watch other male kicked in crotch? Is there universal reaction across male or general population to such video?

There are research articles in the area: http://www.ncbi.nlm.nih.gov/pubmed/19857517

@aandreev - there is a difference between empathy and sensation. If you see someone get kicked in the crotch, and you double over and tearfully cry out, that's not normal.

There has been a study by Jackson, Meltzoff & Decety (2005) who investigated the neurocorrelates involved in the perception of pain.
In order to assess this, they carried out an fMRI study in which their subjects were shown photographs of of feet and hands in situations that are likely to evoke pain and also a control set of photos that were free of any pain evoking stimuli.

Their results display that with the experimental photographs, there is a strong increase in bilateral changes in several regions that we know are involved in the perception of pain, namely:

the anterior cingulate, the anterior insula, the cerebellum, and to a lesser extent the thalamus

Notably, the activity of the anterior cingulate was most strongly correlated with the participants rating of the other persons pain, which suggests that the anterior cingulate is especially modulated according to the subjects reactivity to pain of others.
Source:

Jackson, P. L., Meltzoff, A. N., & Decety, J. (2005). How do we
perceive the pain of others? A window into the neural processes
involved in empathy. NeuroImage, 24, 771-779.
doi:10.1016/j.neuroimage.2004.09.006

Welcome back @jordizambrino (did I spell it right?) Haven't seen you answer for a while :)

@another'Homosapien' well thank you very much! It's good to be back :) (and yes you did)


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Is the problem of cryonics only the pressure?
According to the pop-sci sources which I drew on from, the only problem with freezing whole bodies its that you can't conserve it without freeze-damage.
If you were keeping a cold-blooded animal in a cold surrounding (well, before that removed the parasites somehow) and optimized the pressure in there so to make the cells not to collapse, could you stop all its functions and bring it back to life again later?

Lobsters sometimes wake up after being frozen alive...

@vervet wow...that seems like the problems are mostly about the parasites contained in water (that you should just drain out) - I really do not know anything about lobsters, but compared to other animals the main difference is outter skeleton (it could work as an antiinfective protective cover)...is it so?

"The parasites contained in water"? Could you elaborate? (I suspect part of the reason lobsters have an easier time is their semi-open circulatory systems. Lobsters can't die of internal bleeding.)

@Resonating Interesting indeed, I will look at that. About the parasites: Easier forms of life often survive harder conditions. But originally I wrote it because I said to myself that food in the fridge rot as well, but slower - that's not true for negative temperatures.

The major problem in cryonics is that when an organism is frozen, all of the organism starts freezing. The cell start expanding since ice expands too. The sharp edges of the ice crystals can destroy a lot. Also, your blood would freeze. Again, the sharp edges of the ice crystals would destroy major blood vessels. That is why currently, they have to insert antifreeze into the blood, but it still might not be effective.
Now, to answer your question, many cold-blooded organisms can survive freezing cold temperatures. Some frogs (like the wood frog), for example, have anti-freeze in their blood vessels! So some actually have special adaptations to survive freezing cold temperatures.
I hope this answered your question. Please ask in the comments if you want more information on this. I will gladly research up for you.

Thanks, that's about how I had imagined it. So is it so we really can handle all the other problems nowadays? And about the cold-blodded - they have some kind of salt to keep the blood liquid in colder temperatures, haven't they? (conifers and embryonal-cryonics definitely uses this technique)

@Probably yes,you are correct. Remember, if you like my answer, you can accept it


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Is sexual selection evolutionarily advantageous?
Our biology teacher says that peacocks will soon become extinct because of bigger and bigger (and heavier and heavier) tails. Why natural selection did not eliminate sexual selection?

If that's a direct, unqualified quote your biology teacher doesn't know what he's talking about.

Wasn't there a study showing a correlation between attractiveness of peacock tails and some positive attributes (egg size?) of the offspring? I.e. it is just signalling?

What does "evolutionary advantageous" mean?
First note that is sexual selection evolutionarily advantageous? is a question that makes no sense. An allele or a trait can be evolutionarily advantageous if it increases the fitness of its carrier. If an allele, an evolutionary process or an environmental change decreases the risk of extinction for a species, then you cannot talk about evolutionary advantage. Selection (whether natural, sexual, artificial or whatever) does not (necessarily) minimize the risk of extinction of species.
This post is very related to your question and is definitely worth reading.
I hope your teacher didn't really say that! Assuming he did say that, then know that it is really not as easy as he's suggesting.
There are a number of studies that address the question on whether Sexual Selection (SS) and Natural Selection (NS) have opposite or antagonist effects. The subject is not easy and as SS is not my field of expertise my answer will not be complete. I will talk about two possible hypotheses for explaining the existence of SS and what they mean in terms of probability of extinction.
Good Genes
Under the "Good Gene" hypothesis, females' preference (we'll assume that females are choosy but there are many species where males are choosy) of some traits evolve because those traits are correlated with the global health of the male. In consequence, by choosing a male carrying some trait, the female makes sure that her offsrping will receive good genes from their father. This hypothesis assumes that poor males cannot produce fancy phenotype, while good males can. This is called Zahavi's Handicap Principle.
Under this hypothesis, if a trait become too costly for a given male, the male will just die, therefore limiting the evolution of secondary sexual traits. As a result, the population will no get extinct. Furthermore, under this hypothesis, SS may actually increase the effect of NS making sure that only the best male reproduce. In results the mean absolute fitness of the population should increase faster in a population where "Good gene"-SS occurs.
Sexy Son
Females preference for some trait may also evolve because mating with a sexy male means having sexy sons. This is called the "sexy son" hypothesis.
Under this hypothesis, again if a sexy male has a low enough survival, then a female has better to mate with a less sexy male (even though her offspring won't be very sexy) so to increase the survival of her offspring. After a bunch of generations, all females will end up preference mating with non-sexy male, changing the concept of what we call sexy in this population and therefore reversing the effects of SS.
You may also want to read about Fisher's runaway processes.
Just an article among others
Aneil Agrawal has some nice articles on SS that may interest you. This article for example discusses how sexual antagonist genes influence whether SS has an antagonist or parallel effect to NS.
Is SS really different from NS?
Your question Why natural selection did not eliminate sexual selection? assumes that NS and SS are two different things! This is a very old-style point of view. Charles Darwin coined these two terms thinking of two, unrelated processes. Today, most authors see SS as being part of NS (if a chestnut tree is a type of tree, SS is a type of NS). And many of the processes that are termed SS has actually not much to do with "competition to access a mate" but only has to do with NS. For example, many people talk about SS when talking about sexually antagonist genes or sexual conflicts. In short, the concepts are kind a mixed up. You may want to read about the work of Hannah Kokko about the semantics of terms related to SS.


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Why should the pharyngeal cavity be essential for articulated speech?
In a lecture, I've been told that one of the signs that homo habilis and homo erectus couldn't speak was that they probably lacked the distinction between oral and pharyngeal cavity. But do we really use it, apart from the nasal consonants?

This bit of the book Developmental Neuropsychiatry: Fundamentals describes the difference between the oral cavity in humans and other animals. It doesn't refer to Homo habilis in this context, but it says:

As a result of this anatomical pattern, the range of sounds that an animal can make is limited because of the pharyngeal cavity, which is necessary of sound amplification, is small.

and:

Still, this lower position of the larynx produces a larger pharyngeal space above the vocal chords, which makes possible a greater range of sound modification and becomes the key to the production of articulare speech.

Which suggests that the pharyngeal cavity has a more general use in speech than just making nasal consonants.
This article goes into some detail about Human speech anatomy and its evolution; what it says about the pharyngeal cavity is less about the cavity itself than about the position of the tongue, which allows the separation of that cavity into different sections, leading to different wavelengths being produced. They further say that apes have their tongue entirely in their oral cavity, and are as a result unable to make vowels other than schwas (the basic vowel you make when you're making no effort whatsoever) (they do mention one exception but that species apparently doesn't use its pharynx to make vowels like we do).
The article makes another very interesting point that is relevant to your question, I quote:

Speech communication would be possible without quantal vowels [note from me: the sounds it was talking about that we can make but monkeys can't]. Indeed, there would have been no selective advantage for retaining whatever mutations led to the evolution of the human supralaryngeal vocal tract unless some form of speech had already been part of hominid culture.

That is an excellent point, which is that we need to separate the concept of "speech" from "fully modern speech". Things evolve gradually, and there will have been a continuum from simple communication and vocalizations that our latest common ancestor with other apes likely did, to modern speech with its sounds, grammar, and anatomical and cognitive abilities it implies. And since we no longer have examples of anything on that continuum, we don't know which parts of it we'd be more or less likely to think of as "speech".

Wait...why isn't it possible to articulate without having an extra cavity where the tongue can operat?

If I understand the article correctly it's not about having an extra cavity, it's about the tongue and cavities being in a position where you have two cavities at right angles, and the tongue at the angle between the two able to affect their geometries relative to each other. And the other article refers to a role in sound amplification. It's all about resonant frequencies I figure; in a closed space waves bounce back and forth, and strengthen or weaken themselves depending on their wavelength with respect to the size of the space. Control the size, you control which wavelengths are amplified.


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What were the camels' humps good for back in the polar areas?
I've heard that camels lived in the North America formerly and just in the last few thousands years they've migrated to the hot deserts. Thus they allegedly utilized the adaptations against the cold weather in the tropics.
One of this adaptations have been their humps. Clearly, it is useful not to have a thick fat layer all over your body in the hot weather. (I see it like a neural spine sail (which helps with thermoregulation to the desert fauna).) But how about the polar areas? All the other polar animals don't see to be restricted by the fact they save all the fat under their skin in any way.
So what were the original reason for the evolution of the camels' humps?

Do you have a reference for "Clearly, it is useful not to have a thick fat layer all over your body in the hot weather."?

@kmm I suppose so, since nomads don't wear fury coats, but I think I don't really catch the whole concept, so there is probably a different reason.

In my opinion there might be two reasons why the camel hump (rather than bump) might be one of the adequate adaptations of camels to living in the cold (additional to their flat feet giving hold on both snow and sand and tooth structure, Rybczynski et al., 2012). Both match the humps being fat storages in modern camels.
The first is also provided by Rybczynski et al. (2012):

Their iconic hump(s), containing fat, also may have been adaptive. As seen in high-latitude ungulates today (Parker et al., 2009), fat deposits could have been
  critically important for allowing populations to survive and reproduce in harsh climates characterized by 6-month long, cold, winters.

Note that this refers to the nutritional value of the fat deposits and does not necessarily relate to maintaining body temperature.
The difference to modern camels would be that the fat storage in modern-day camels serves indirect water deposition (water can be easily gained from the fat stored in the humps and storing the water condensed in fat molecules is way more efficient than storing water directly). This relates to the second reason which, however, is more speculative from my part.
Cold - especially in plants - also implies drought as frozen water is not available. This does not need to apply to mammals as they can thaw ice, e.g. by licking. However, this might be critical as the body might lose some temperature during that process. Accordingly, fat storage might already then have been a means to storing water while keeping body temperature.
Alternatively, and maybe even more likely, the camel hump might have undergone a switch in function from storing a food source in archaic camels to storing water in modern camels as both can be achieved with fat deposits due to the chemical properties of fat.

Beat me to it by seconds! Was even going to use the same reference. Well played, sir... :-)

Is there actually a good support for the hypothesis that many of the particular camel features have evolved in a cold environment or is it still just a good hypothesis?

@AlexDeLarge Ok, I have heard about the water acquisition by decomposing the fats. But about the first reason: Surely, fat is used as a nutritional storage in all mamalls but what is the advantage of storing it into a single place? Other polar animals play the opposite strategy.

@Remi.b: I am not a camel expert but as far as I know the paper cited in my answer (and some fossil record papers) is pretty much what is out there. The evidence that ancestors of modern camels evolved in arctic areas seems to be strong. What traits actually evolved in response to cold does not seem to be clear.

@Probably: I don't know. Might be that there is absolutely none. In cases like this, I often think that the contingency of evolution is the most plausible explanation. There is, however, one thing I could think of (again, speculative). According to the cited paper, camels evolved during a warm period - eventually indicating that there were harsh, cold winters but mild summers. Unlike in todays 'always cold'-arctic where a layer of fat is nice, this could have been disadvantageous in the warmer summers compared to a condensed storing in the humps.

@AlexDeLarge Ok, thank you, I'll read the paper and wait if someone comes with a better explanation.


text:
Why are there relatively more predators on the land than in the oceans?
Our biology teacher told us that among worse conditions one of the reason that intelligent life had actually evolved on land is that there is a more important selective pressure due to the bigger number of predators.
Is there really relatively fewer predators (in numbers) on the land? What is the cause of this phenomenon?

I wouldn't say that conditions are poorer on land, but it's definitely more diverse (as you say). But I'm not sure that this is the cause, as I think many of the fish species are predators to other fish species or marine organisms and microorganisms. And although I don't agree with the term "intelligent life", we do have marine organisms, such as dolphins, for which we give anthropocentrically intelligent characteristics.

Check this out. It won't answer your question on the predators, but maybe give some more ideas and opinions on the matter of intelligent life (just found it looking after I saw your question): http://www.pbs.org/wgbh/evolution/humans/intlife/index.html?fy

@BioGeo Thanks but I actually argued that marine is more diverse (I imagined harsh conditions such as a desert or polar areas :) but you're right, maybe I can imagine better that there are lot more diverse climates due to the changing climate on the land

Is the question "Are the more predators on land? (In (relative?) number of species or in (relative?) number of individuals?)" or is it "Why are there more predators on land?". If the question is the second one, then a citation is needed but I guess you are rather asking the first (on of the first actually) question.

I wouldn't say conditions on land are poorer... just more unstable, less predictable over a span of a million years. And an unstable environment appears to be one of the factors in the evolution of human intelligence. ie the environment changes faster than evolution can adapt the body... so one solution is to adapt the animal's behavior which requires intelligence.
That said, dolphins too are plenty intelligent. Octopus also are quite good puzzle solvers.. but are short lived.
As for predator -prey ratio https://www.mcgill.ca/newsroom/channels/news/why-arent-there-more-lions-254873 Here is something to read. Predator-prey ratio appear to be govern by the rate of growth of prey items
And prey in the ocean has a faster turn around in the ocean.. so there are more predators in the ocean than on land. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4240998/.

Sorry, I think you haven't answered the question (I'm sorry for bad formulation) if there is bigger predator-prey ratio on land.

The ratio of predator to prey is higher in the ocean than it is on land. So the predator prey ratio is not the cause for intelligence.


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Why does black and yellow indicate danger?
It is a well-known fact that combination of black and yellow indicates danger or poisonousness.

In western society it seems obvious this comes from bees and wasps, but it seems like many tropical frogs use yellow and black. Black and yellow also indicates toxicity in some fish species and the order of the colors seems to communicate whether we see a harmless milk snake or a venomous coral snake.

So which came first: the fear of black and yellow or the color of bees? Are there any studies about the color combinations effect on human brain? Is it learned or congenital?

I think it is more to do with contrast between Black and Yellow which is important that color itself. This contrast creates optic flow. Most of these organisms use change in optic flow for either navigation or predator detection. We use black and white gratings to scare zebra fish :P I am pretty sure they will invoke same response for Back and Yellow gratings.

@Dexter Wow, that's a good point. You're right, gepards, panters or tigers also use this pattern. Yet I think I will stay with the claim, that it is just a product of sexual selection as it is evolutionary so disadvantageous.

Not only yellow and black, white and red is common as well...

@Probably Could you explain why you think it might be sexual selection??

@rg255 Yes! Since Tabmath has suggested the camuflage I am not sure about it, but in priciple, runaway selection often stands behind the evolution of this coloring.

I think you are perhaps misguided @probably - sexual selection often leads to extreme traits, but it is not the only cause of extreme traits. Fpr example: colour might act as a warning to predators which learn what is poisonous - predators will then not eat the brightly colored animals because they won't get benefit from doing so. For the same reason we see mimicry, non-poisonous species using the same conspicuous colours to make predators hesitate.

First of all, great question! What you describe here is known as aposematism. Aposematism is the adapation of warning signals against the predator. This word is used for any sound, coloring, and odor used as a warning signal. Of course, for this question the focus is color.
Honest indications
Animal coloration is usually an honest indication of their noxiousness. The brighter they are, the more noxious and toxic they are (http://rspb.royalsocietypublishing.org/content/276/1658/871). In the linked article, there are many references one this positive correlation of toxicity of prey to predator and the brightness of the coloration. In the article they use mathematical models to support the mathemstical evidence. But one thing is for sure: bright colors do mean the prey is armed with defenses, whether the correlation is positive or not.
Why then is it black and yellow?
The conspicuousness of the coloration is very important because it is important to see from a far away distance. The reason colors like yellow and black are used is because (http://rspb.royalsocietypublishing.org/content/279/1728/417):

— They provide high contrast against the background (e.g. red/yellow against green foliage), which promotes detection.
— They are resistant to shadows (which are rich in blue-UV), and to changes in illumination (e.g. black should not change during day, whereas white could become ‘pink’ at sunset and sunrise). Therefore, they provide a reliable signal under varied habitats and light conditions.
— Yellow/red and black has both high chromatic and luminance contrast.
— Such colours may allow distance-dependent camouflage if yellow/red and black ‘blend’ to an average colour that matches the background at a distance when predator vision is no longer sufficient to discriminate individual marking components.
— Such colours are distinctive from profitable species.

What about the combination of black and yellow?
In the same article, they mention that:

Many warningly coloured prey have markings comprising repeated pattern elements. Such arrangements in signal structure may increase redundancy in the signal but improve the likelihood that the strategic component will be detected by the receiver. In addition, repeated elements may be rare in many natural environments, thus increasing conspicuousness of the prey animal. Simple pattern components (such as stripes and spots) may facilitate detection and also speed up avoidance learning if they are easier to memorize.

The research seem to show that the patterns, such as the stripes, lead to increased avoidance, but it is not sure whether or not it is due to the stripes itself or due to the constrast of the black and yellow.
I hope I have answered your question and if you have any questions, feel free to ask in the comments.

@TannMath Thanks! Do you think that the fact leopards, tigers and cheetahs use also black and yellow is a coincidence caused by sexual selection?

@Probably well this research was done mainly for prey animals... the main hypothesis for leopards and tigers is that it allows them to hid in their environment better, allowing them to pounce on their prey

Sorry for the late response....  I think the short answer is Game Theory.  Obviously any colour scheme could in principle be used to signal toxicity.  However, if a scheme was chosen that did not stand out it would not be an Evolutionary Stable Strategy (ESS).
Let's take an example.  Suppose a poisonous insect was coloured with green and brown markings.  This is good camouflage since green is the colour of chlorophyll and brown the colour of mud.  Therefore there would be zero downside to a non-poisonous species to mimic the markings of the poisonous species.  Eventually individuals from the non-poisonous species with the markings would massively outnumber individuals from the poisonous species, and brave predators would start eating insects with those markings.  If, on the other hand, the poisonous species chose a colour scheme that made it stick out, there would be a cost associated with mimicry, and in the Nash equilibrium the proportion of species that mimic the markings would be smaller.
In game theory any signalling without an associated cost is known as "cheap talk".  An example is where you go to an auction and before the bidding starts you go around telling everyone "I have a lot of money and I really want this item".  No one will believe you because, well, you would have said that wouldn't you!  However, if before the bidding starts you pull out a Havana cigar and light it with a $100 note, that's not cheap talk, and will probably cause a number of your competitors to quietly back off.

PS: I highly recommend the book "Game Theory: A Very Short Introduction".  Although the example I've given isn't in the book, the book does contain lots of other successful applications of game theory to biology.  In fact GT is probably more successful in  biology than in economics.


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Why does UVA penetrate deeper than UVB, though it's weaker?
Even though UVA radiation ranges in longer wavelengths (315–400 nm) than UVB (280–315 nm) and thus is less energetic, UVA is able to penetrate deeper into the skin and even reach the dermis. Why is there such a discrepancy?

Melanin itself may absorb more UVB? I speculate...

It's not simply a matter of energy, otherwise we wouldn't see different colors of transparent materials.  Different molecules &c preferrentially absorb different wavelenghts.  Probably there's nothing in the skin that absorbs UVA, just as lighter-skinned people don't have much that absorbs visible light.

This answer may be pertinent: Interaction of radiation with the body.

Our skin contains quite a lot of water and I think this is answers the question: The absorption of UV light by this water goes drastically up when you shift to shorter wavelengts with a minimum absorption in the UV-A spectrum.
See this figure (from here):

So water has a very low absorption around 340-350nm (UV-A) and a very high absorption at shorter wavelength (UV-B and UV-C). This also explains why we get a lot more UV-A through the atmosphere than for harder UV-Radiation.


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Why do we like to touch fluffy things?
I read this article but it didn't explain much. Is the fact people like to cuddle pets with fur connected anyhow with our past when our ancestors had fur as well - and therefore could evolve an instict to enjoy hugging someone furry as an expression of friendship.

You should include some more background from the linked article, to make this less "opinion-based" (since its currently being VTCed on these grounds now).

I wouldn’t touch a furry animal — its fur is probably crawling with insects carrying disease. Get a grip — fluffy things — are you a grown man or a child?

I'm voting to close this question as off-topic because it’s trivial and stupid.

An answer I got from Jan Kolář of Charles University:

I'm not sure that people prefer fluffy things just from the fact that
  they are fluffy. They like things that are soft to touch such like
  pillows. The popularity of fluffy things might have a simple
  explanation: There's no danger of getting cut.

So the fact we like to cuddle with dogs and cats has probably nothing to do with our furry past.

It's sensorily similar to "why do people love to eat crunchy things?". Shops contain thousands of the most crispy foods. Crunchy foods and fluffy material like velvet have a common attribute. that they can both generate thousands of complex nerve responses. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1745-4603.1995.tb00782.x
Crispy foods generate nerve responses above 5KHz, and if you feel velvet with your fingers it has a similar effect. It's a kind of vibration, perhaps what they call vibrotactile.
Today they make haptic feedback with vibrotactile actuators, like a console gamepad, which is also designed to be pleasant.

Hi, thanks for your contribution. Have you got anything to base the hyporthesis fluffiness is similar?

Also, is there really no deeper explanation when it goes to crispiness? Is it something useless evolution just hasn't got ridden of yet?

Perhaps there is a social element that is common to mammals. It wouls be nice if there was a mechanical or physical explanation for nerve ending, synapse and cerebral effects, but science doesn't seem to have obvioys theories for it, it's even more mysterious than tickling.


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Is the birds' decision to fly away congenital or learned behaviour?
I see two possibilities how could the birds know what to do every fall:

The birds' migrations are driven entirely by the vertical memetics and today it is just a custom transferred from parents to offsprings.
There is a gene that causes birds to decide to fly to the warmer areas every fall, activated when it is appropriate time

Which of these hypothesis is closer to the truth?

The first hypothesis seems very unclear. I think you just mean that migration direction/distance/timing/etc.. could be a learned behaviour. However, you phrased it weirdly. You seem to poorly use the term macroevolution as well.

@Remi.b That's the original meaning of "macroevolution", isn't it? The process of preserving of successful families, packs and species. So this is exactly what should be responsible for the spread of this custom. But it is'nt entirely needed for the question.

@Probably I'm not the only one that finds discussing memes in this sense a pseudoscientific endeavour (Wiki of the criticisms). I think "learned behaviour" is a better term.

I think the question is clear now (+1). You might want to clarify that this is a nature vs nurture (or learned vs innate) question. The answer will likely depends on the species though.

This example proves IMHO that migration is largely nature and not nurture:
In the Netherlands, white storks were bred / reintroduced. A large part (about one third?) of the reintroduced birds do not migrate, but their offspring usually does migrate see. They couldn't have learned it from their parents, that's for sure.

Does it mean, that they have a circaannual biorhytms or do they detect the factors of changing weather such like temperature (if so, we could try to put them into a cold environment and see wheter they would fly south (or north in case of the southern-hemisphere birds)?

@Probably I thought your  question is if the behaviour is learned or genetic. What triggers migration is a totally different question.

I'm just interested how does it work. The mechanism is a direct consequence of the genetic code. But I agree I could find it in the quoted article.


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How big advantage had a trait have to bring to evolve in the human evolution?
Yes, I've heard that we have evolved from the common ancestor with primates as intesively, as the chimpanzees. Sometimes I read about some enormously complex traits, evolutionary psychologists think have evolved in humans, such like religion, night owls or art (which don't seem to require a specific complex mutation). On the other hand we still grow many unnecessary organs, so I really wonder: What is the percentage advantage a trait had to provide to humans (so that no other species share it) to actually evolve continuously?
OR (I'm not sure if it can be calculated generally) I can get by with this question: What is the correct formula how to calculate the average probability of survival a trait had to increase to preserve over some time (with the gene expression calculated in it)?

"we still grow many unnecessary organs" - huh? Which organs are unnecessary? The liver? Kidneys? Stomach?

I think a clear way to rephrase this question would be "How beneficial a mutation needs to be to behave really differently from neutral mutations?". I am answering to this question.
Neutral mutations and nearly neutral mutations
The probability of fixation of a new neutral mutation is $P_{neutral}=\frac{1}{2N}$, where $N$ is the population size. An intuitive way to understand why this is true is that, after an infinite amount of time (constant population size and in absence of speciation), the whole population will necessarily descend from a single individual. In absence of selection pressure every single individual has the same probability to be the ancestor. As a fraction of $\frac{1}{2N}$ of the population is carrying the mutant allele when it first occur, then the probability that his allele reaches fixation is $\frac{1}{2N}$. In fact, this result can be generalize to say that the probability of fixation of a neutral mutation present at frequency $p$ at a given time in the population has a probability $P_{neutral}=p$ to get fixed.
Given the selection coefficient $s$, a good approximation is that whenever $2Ns<<1$, then the probability of fixation is essentially not different from $P_{neutral}$.
This qualitative boundary ($2Ns<<1$ or $2Ns>>1$) is the boundary you were interested in. In your post you talk about "percentage advantage". This percentage advantage is just $s\cdot 100$.
Beneficial mutations
For "significantly" beneficial mutations, a good approximation to the probability of fixation of a newly arisen mutation given $s$ and $N$ is
$$\frac{1-e^{-s}}{1-e^{-2Ns}}$$
Source of information
Your question shows a few misunderstanding and is nested within the field of population genetics. Plus, in absence of good understanding equations and just vague symbols. I recommend that you have a look at an introductory source of information in population genetics. You will find recommendation of books in population genetics here. For a complete and relatively accessible (might still be a bit complicated) introduction to population genetics, I would recommend  Gillespie's Population Genetics: A Concise Guide for you. This book will so offer proofs for the equations I gave you above.

Sorry, I don't understand what does the N mean. But thanks for rewriting the question. And about the neutral mutation: Shouldn't the probability be just random? There is nothing else we can say about an individual with a neutral mutation, except from he has something that doesn't affect his fitnes.

Sorry, I forgot to indicate what $N$ means. $N$ is the population size. To make it more general $N$ should be replaced with the effective population size $Ne$.

You said Shouldn't the probability be just random?. This sentence makes no sense. You either don't understand the definition of "probability" or of "random" (or both). If a probability is different from 0 or 1, then there is randomness (=stochasticity). Yes, the probability of fixation of a mutation (neutral or not) is subject to certain level of stochasticity in finite populations (it is the very nature of genetic drift at play).

Yeah, sorry, I meant probability 0,5. It's the same probability that the bearer of my gene is a good one, as that he is a looser (comparing to the rest of the population). So the equation should somehow work only for population of 1 individual.

I added an intuitive explanation for why the probability of fixation of a newly arisen neutral mutation is $/frac{1}{2N}$. This equation holds true for a population of any size (however should be more correct to talk about "effective population size" but I did not want to add another concept you might not know of).


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Is there any definition of life which makes viruses undeterminable?
There are many different definitions of life (RNA, something that comes through evolution) but not one I have seen which could not determine wheter viruses are living things (even though there are many definitions both for YES and NO). Are there any such definitions (I'm looking for cases where it's really fundamental debate, not only struggling for the correct dictionary definition)?
Thank you.

Can you please clarify your question? At the moment it is (at least to me) not clear what you are asking about.

There is nothing in knowing whether viruses are alive or not but a struggle over accepting a definition or another. Have a look at why isn't a virus alive? for more info.

Your last sentence is the key: defining life really is just finding a dictionary definition that we can agree upon. Biology is something that defies discrete definitions at times: "What is it to be alive?" "What is a species?" maybe even "What is the wild type allele of a gene?"
I would recommend not looking at viruses as a challenge to determine if they are alive or not so much as an excellent opportunity to discuss what we think are important characteristics of life.
Life can alternately be described as:
"Comprised of self-replicating cells" (a paraphrase of the "Cell Theory of Life"
or
As things that embody at least most of the following characteristics:
1. Self-Replicating
2. Metabolizing
3. Growing
4. Showing signs of adaptation
5. Being organized
6. Respond to their environment
7. Being comprised of cells
I like to think that we should focus on extraterrestrial forms when we define life. i.e. what would we want to see in an extraterrestrial in order to call it 'life'? While some are troubled by calling viruses alive here on earth, the same people might be willing to say that we have found extraterrestrial life on another planet if it was similar (granted, it's hard to imagine this kind of life existing without a host...)
as an aside: You might also ask whether this question is fit for this stack as it can not be supported by literature references (at least none that would actually support a conclusion). So should this be posted as 'Biology' or 'Philosophy'?


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Task-dependent "reversed" handedness: why use left hand for some tasks? How is it controlled by the brain?
I am right-handed. Which means that when I hammer down a nail, I hold the nail in my left hand, with which I can hold it straight and at a controlled position.
This is true in situations where the task of holding something in place is  simultaneous with a more complex task, such has hammering, done with the right hand. But I note that even when there is no other task, I personally use my left hand to hold in place, e.g., a  bottle that I am filling up in a stream of water.
To generalize a little, it seems to me that while I use my right hand for precise motion or applying a force, I'll use my left hand to maintain a position against forces.
Is this behaviour something documented? Does one develop specific brain control to implement this controlled-position tasks?

The dynamic-dominance hypothesis of handedness states that the essential factor that distinguishes dominant from nondominant arm performance is the facility governing the control of limb dynamics. Sainburg (1) writes that

It should be noted that dominant arm advantages do not apply to all
  tasks, or all aspects of tasks. Healey et al. (1986) examined an
  extensive range of tasks and found that four factors or groups of
  tasks accounted for 80% of the variance in hand preference among the
  110 subjects tested. Tasks that were almost exclusively associated
  with dominant arm use included activities requiring precision in
  interjoint coordination and trajectory formation. (...) In contrast,
  tasks that involved spatially orienting a body segment posture were
  more often performed with the nondominant arm. These tasks included
  posturing the hand to point toward a distant object, which is similar
  to other functional tasks such as holding a piece of paper that is
  being cut with scissors, or orienting the hand in space for catching a
  baseball. Such postural orientation tasks are less dependent on
  intersegmental dynamics, since the trajectory used to attain the
  posture is not critical for task success. The dynamic dominance
  hypothesis thus appears to account for the extent to which hand
  preferences for specific activities are lateralized.

This appears to be consistent with your experience.


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What is this wood-infesting insect?
I have these insects in a very old wooden floor. I would like to know whether they are possibly termites, and if not, what they are.

They are about 4 mm in length (and I've had difficulty taking a picture with a standard camera, I may be able to get a better one in a couple of days). This one is dead and may have been crushed a little. Another sign of their presence is little heaps of wood dust appearing with a periodicity of 24-48 hrs, which are about 1 cm in diameter.
Following the indications of @usr137, I think it's rather an ant, indeed it has a slender mid-portion of the body, corresponding to detail (4) in this termite/ant comparative:

But they are much smaller than the ranges I find for carpenter ants (6—19 mm).

sounds like termites to me - it would be best to get an exterminator to come and take a look.

I'm asking because pictures of wood-infesting termites I've found around the internet don't look like this, but there seems to be a large variety. We have definitely planned to have someone come and tell us what to do.

That picture looks more like an ant. Carpenter ant maybe?

@user137: the abdomen is very long and thin, not really like the ants I'm used to around here (S-E France). And I don't know that ants will dig hard dry wood at that rate?

@user137: actually, reading about carpenter ants you may very well be right! The abnomen I see is longer than what is documented, and they are smaller too, though. I'll investigate this further, thanks.

Note that the Wolfram image identifier got it right even with this rather poor photo! Quite amazing -- unless it used bio.SE to acquire its knowledge of carpenter ant and is simply repeating what we came to here...?

To close this, we're now reasonnably sure that they were carpenter ants or a close relative. One more clue is that they infested the wood close to a window receiving sunshine and were much more active when it was warm there. Thanks to @user137.


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Do mosquitoes squeeze in?
Practical motivation: I have equipped part of my windows with mosquito nets. Despite not opening the unequipped ones at night, I still have mosquitoes entering my flat. To decide whether I equip all windows with nets, I am wondering whether mosquitoes are likely to take advantage of other ways to enter the place: it is a 3-century old building, and in no way air tight. There is likely to remain gaps of about 2 mm width in many places, both at some edges of mosquito nets (although I could improve on these) but also around front door, etc.
Zoology questions :
Given the strategy I observe for mosquitoes who fly upfront to the net and explore randomly while hitting the net repeatedly, I am not sure they may detect a small opening away from larger ones, or will they?
I am also unsure whether they would squeeze for a distance longer than a few mm, since they do not appear to ever walk or crawl but only fly?


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Strictly from a biological perspective, what is the functional expectation of a human being
Just like the title says: Strictly from a biological perspective, what is the functional expectation of a human being.
No religious or philosophy-based answers will be accepted, we are talking biology not religion or philosophy.
Answers involving excessive psychology will be frowned upon unless found to be exceedingly insightful. (The brain is a biological entity)
If you are considering claiming this to be too broad or unanswerable consider the hypothetical question "what are the functional expectations of human feet" which can be answered fairly easily by a child with no formal training in biology. In my actual question I simply ask about the feet and the other parts attached to them.
Edit: Originally this question was titled "Strictly from a biological perspective, what is the purpose of a human existence." To clarify the question i have changed it to "Strictly from a biological perspective, what is the functional expectation of a human being."
Despite the concerns raised with the use of the word "purpose" the question was serving its purpose with the answers I am seeing.  I did have  some reservations about the word "purpose" as well, but I thought I would try it and see what others thought.
So if a human stomach has the overall functional expectation of mechanically and chemically breaking down and digesting food, what would be the overall functional expectation of a human as a whole? I am looking for not so much of psychologically specific functional expectations and more of physical functional expectations.
For instance a house cat's functional expectations are generally considered to be sleeping, eating, reproducing, socializing, hunting, etc.

Adding the line "from a biological perspective" does not make this any less of a philosophical question. I would argue that the question "what is the purpose of feet" is also philosophical, but as shorthand most people will interpret that as 'what function(s) do feet serve the body' which is a biological question. It doesnt work for your question. What function do humans serve _____? Serve what? Serve themselves? Serve elephants? This question is too broad if biological, off topic if philosophical

Although "What is the purpose of human feet" and "What is the purpose of human existence" have the same word pattern, they are quite distinct English sentences, even before the biology question.  The first can be answered with what good feet do for people.  The second asks what good people do for  something (what?)  I would -1 this if I had the rep on this site (I have lots on math) Looks like a troll to me.  Biology and purpose rarely belong in the same sentence.

I think maybe the question is badly phrased.  You may want to rephrase without using the word "purpose", which implies a rationally-planned intention before the development of the item to which purpose is ascribed.  As biology does not accept that any such rational planning occurred, strictly speaking nothing can be said to have purpose in a biological context.

First you have to define "purpose"...

Sorry guys I don't see any way of further modifying the question without changing the intent of the question. It is an important question and was answered well. Do whatever needs to be done.

I will start with a quote from François Jacob, a French geneticist:

The sole ambition of a bacterium is to make two bacteria.

The same reasoning can be extended to all life on Earth, including humans.
There is no purpose to human existence, in the same way that there is no purpose for life at all. Life is there because it can. It works, chemically, physically and thermodynamically, given the physical conditions present on Earth.
Biology does not give any moral reason for our existence. It only describes what is there. Using experimental techniques we can infer the purpose of the human feet. All we need to do is to remove the feet of a human subject and see what happens. The subject will be unable to walk, and therefore we will be able to infer that the feet's purpose is to enable locomotion. In biological research, we usually remove or silence genes or proteins from an organism to infer their purpose. We then observe the phenotype. Most of the time however, such an experiment does not give any information on the purpose of the gene because its function is not obvious enough to be observed.
In the same vein, one could remove humans from the Earth and see what happens. If something changes for the worse on Earth, then we would be able to infer that our purpose was to prevent such event from happening. Obviously, such an experiment is impossible to perform, therefore we will never know what is our purpose, neither will we know whether we actually have a purpose.

I would have given a two-word answer ("To reproduce."), but +1 for making the answer long enough to satisfy stackexchange requirements and even throwing in an apropos quote.

Purpose requires a sentient being to have intent.  There is no biological reason to suppose there is any purposeful intent behind life.
If you hold otherwise, perhaps inquire of the fellow or lady or other you suppose is responsible.
Just because a child can give an answer to a question doesn't mean that the answer is accurate, or that the question truly is well-formed enough to answer well.

+1.  That there is an evolutionary benefit to feet does not imply that they have a purpose, as purpose requires forethought.  The same can be said of life's tendency to reproduce itself: you can argue that it is a basic characteristic of life, but that doesn't elevate it to the status of a purpose, because purpose implies design and there is no scientific basis for believing that any such design occurred.

In the context of evolution, the only "purpose" that a thing can serve is the role it plays in the process of reproduction, selection and mutation.
So, "what purpose do feet serve"? Naively: the formation of part of the human body as feet serves to increase the likelihood of the survival and reproduction of humans, by supporting the way we move and stand. Even more naively, the child wouldn't talk about survival and reproduction -- to a child the purpose of something is whatever benefit it is seen to cause, so the purpose of feet would be "walking".
"What purpose do humans serve"? Naively: to survive and reproduce. With more nuance, since we know about symbiotic evolution: to increase the likelihood of the survival and reproduction of various species, including but not limited to humans. For example humans have been pretty bad news for North American magafauna, but pretty good news for wheat.
On this basis of symbiosis you could reasonably conclude that the "purpose" of animals (or at any rate most bilateral animals) is to serve as a habitat and food-gathering mechanism for their gut-flora. Or that the "purpose" of most eukaryotes is to do the same for mitochondria. Or less fancifully, that the "purpose" of living organisms is to provide a stable environment for RNA and DNA to reproduce.
It's ultimately a question of perspective and as such subjective. "Purpose" really implies intent, which absent religion or philosophy is pretty hard to pin down. But when talking about feet and other biological characteristics we use "purpose" as a shorthand for "benefit which explains their being selected for".
As such, providing an environment for DNA to reproduce is right up there as a candidate for the purpose of life in general, including humans. Humans then are a variation within this general goal, that seems to be doing OK for the time being. This is more or less the theme of The Selfish Gene. You can easily question Dawkins's views on religion and philosophy, but (despite some disagreement) his ideas on genetics were pretty well received as far as they went.

That all depends on the perspective from which you view the question. For example, from the perspective of a human being the purpose of human existence may be to make more humans. From the perspective of a herd of goats the purpose for human existence is for the humans to bring food and water, care for kids, shovel out the barn, talk nicely to them, scratch them behind the horns where they can't reach, and give them something to snicker at. Cats are much the same but will sometimes allow their bellies to be scratched, don't have horns, and are to the best of my knowledge unable to snicker.
And of course all this assumes, on what only be termed hear-say evidence, that humans exist. "Ah", you say, "but I am real - I have form - I have substance - of course I, and by extension the entire human race, and in fact the entire universe, exist!". Perhaps, but then again perhaps not. What if what you perceive as existence is merely the by-product of intestinal gas disturbing the slumbers of a god-like creature whose vagrant dreams can morph into something approaching reality, but which vanish like a popping soap bubble when the god awakes?