My wife is pregnant right now with our first child, and when people see her with her big baby bump, the first question people ask, almost without fail, is, "Is it a boy or is it a girl?"
Now, there are some assumptions behind that question that we take for granted because of our familiarity with our own human biology.
For human babies, we take it for granted that there's a 50/50 chance of either answer, boy or girl.
But why is it that way?
Well, the answer depends on the sex determination system that has evolved for our species.
You see, for most mammals, the sex of a baby is determined genetically with the XY chromosome system.
Mammals have a pair of sex chromosomes, one passed down from mom, and one from dad.
A pair of X's gives us a girl, and an X and a Y together gives us a boy.
Since females only have X's to pass on in their egg cells, and males can give either an X or a Y in their sperm cells, the sex is determined by the father and the chance of producing a male or a female is 50/50.
This system has worked well for mammals, but throughout the tree of life, we can see other systems that have worked just as well for other animals.
There are other groups of animals that also have genetic sex determination, but their systems can be pretty different from ours.
Birds and some reptiles have their sex genetically determined, but instead of the sex being determined by dad, their sex is determined by mom.
In those groups, a pair of Z sex chromosomes produces a male, so these males only have Z's to give.
However, in these animals, one Z and one W chromosome together, as a pair, produces a female.
In this system, the chance of a male or a female is still 50/50, it just depends on whether mom puts a Z or a W into her egg.
Certain groups have taken genetic sex determination in completely other directions.
Ants, for example, have one of the most interesting systems for determining sex, and because of it, if you are a male ant, you do not have a father.
In an ant colony, there are dramatic divisions of labor.
There are soldiers that defend the colony, there are workers that collect food, clean the nest and care for the young, and there's a queen and a small group of male reproductives.
Now, the queen will mate and then store sperm from the males.
And this is where the system gets really interesting.
If the queen uses the stored sperm to fertilize an egg, then that egg will grow up to become female.
However, if she lays an egg without fertilizing it, then that egg will still grow up to be an ant, but it will always be a male.
So you see, it's impossible for male ants to have fathers.
And male ants live their life like this, with only one copy of every gene, much like a walking sex cell.
This system is called a haplodiploid system, and we see it not only in ants, but also in other highly social insects like bees and wasps.
Since our own sex is determined by genes, and we do know of these other animals that have their sex determined by genes, it's easy to assume that for all animals the sex of their babies still must be determined by genetics.
However, for some animals, the question of whether it will be a boy or a girl has nothing to do with genes at all, and it can depend on something like the weather.
These are animals like alligators and most turtles.
In these animals, the sex of an embryo in a developing egg is determined by the temperature.
In these species, the sex of the baby is not yet determined when the egg is laid, and it remains undetermined until sometime in the middle of the overall development period, when a critical time is reached.
And during this time, the sex is completely determined by temperature in the nest.
In painted turtles, for example, warm temperatures above the critical temperature will produce females within the eggs, and cool temperatures will produce a male.
I'm not sure who came up with this mnemonic, but you can remember that when it comes to painted turtles, they are all hot chicks and cool dudes.
For some tropical fish, the question of will it be a boy or will it be a girl isn't settled until even later in life.
You see, clownfish all start out their lives as males, However, as they mature, they become female.
They also spend their lives in small groups with a strict dominance hierarchy where only the most dominant male and female reproduce.
And amazingly, if the dominant female in the group dies, the largest and most dominant male will then quickly become female and take her place, and all of the other males will move up one rank in the hierarchy.
In another very different ocean animal, the green spoonworm, the sex of the babies is determined by a completely different aspect of the environment.
For this species, it is simply a matter of where a larva happens to randomly fall on the sea floor.
If a larva lands on the open sea floor, then it will become a female.
But if it lands on top of a female, then it will become a male.
So for some species, the question of boy or girl is answered by genetics.
For others, it's answered by the environment.
And for others still, they don't even bother with the cwalker@example.org.
Take whiptail lizards, for example.
For those desert lizards, the answer is easy.
It's a girl.
It's always a girl.
They are a nearly all-female species, and although they still lay eggs, these eggs hatch out female clones of themselves.
So will it be a girl or will it be a boy?
Throughout the entire animal kingdom, it does really all depend on the system of sex determination.
For humans, that system is a genetic XY system.
And for me and my wife, we found out it's going to be a baby boy.
(Kiss)
Eight years ago, I was haunted by an evil spirit.
I was 25 at the time, and I was living in a tiny house behind someone else's house in Los Angeles.
It was this guest house, it had kind of been dilapidated, not taken care of for a long time.
And one night, I was sitting there and I got this really spooky feeling, kind of the feeling like you're being watched.
But no one was there except my two dogs, and they were just chewing their feet.
And I looked around.
No one was there.
And I thought, OK, it's just my imagination.
But the feeling just kept getting worse, and I started to feel this pressure in my chest, sort of like the feeling when you get bad news.
But it started to sink lower and lower and almost hurt.
And over the course of that week, this feeling got worse and worse, and I started to become convinced that something was there in my little guest house, haunting me.
And I started to hear these sounds, this "whoosh," kind of whisper, like something passing through me.
I called my best friend, Claire, and said, "I know this is going to sound crazy, but, um ...
I think there's a ghost in my house, and I need to get rid of it."
And she said -- she's very open-minded -- and she said, "I don't think you're crazy.
I think you just need to do a cleansing ritual."
(Laughter) "So get some sage and burn it, and tell it to go away."
So I said, "OK," and I went and I bought sage.
I had never done this before, so I set the sage on fire, waved it about, and said, "Go away!
This is my house!
I live here.
You don't live here!"
But the feeling stayed.
Nothing got better.
And then I started to think, OK, well now this thing is probably just laughing at me, because it hasn't left, and I probably just look like this impotent, powerless thing that couldn't get it to go away.
So every day I'd come home and you guys, this feeling got so bad that -- I mean, I'm laughing at it now -- but I would sit there in bed and cry every night.
And the feeling on my chest got worse and worse.
It was physically painful.
And I even went to a psychiatrist and tried to get her to prescribe me medicine, and she wouldn't just because I don't have schizophrenia, OK.
(Laughter) So finally I got on the internet, and I Googled "hauntings."
And I came upon this forum of ghost hunters.
But these were a special kind of ghost hunters -- they were skeptics.
They believed that every case of ghosts that they had investigated so far had been explained away by science.
And I was like, "OK, smart guys, this is what's happening to me, and if you have an explanation for me, I would love to hear it."
And one of them said, "OK.
Um, have you heard of carbon monoxide poisoning?"
And I said, "Yeah.
Like, gas poisoning?"
Carbon monoxide poisoning is when you have a gas leak leaking into your home.
I looked it up, and the symptoms of carbon monoxide poisoning include a pressure on your chest, auditory hallucinations -- whoosh -- and an unexplained feeling of dread.
So that night, I called the gas company.
I said, "I have an emergency.
I need you to come out.
I don't want to get into the story now, but I need you to come out."
(Laughter) They came out.
I said, "I suspect a gas leak."
They brought their carbon monoxide detector, and the man said, "It's a really good thing that you called us tonight, because you could have been dead very soon."
Thirty-seven percent of Americans believe in haunted houses, and I wonder how many of them have been in one and how many of them have been in danger.
So that haunting story has led me to my job.
I'm an investigator, and I'm an investigator in two senses: I'm an investigative journalist, and I'm also an investigator of the claims of the paranormal and claims of the spiritual.
And that means a few things.
Sometimes that means that I'm pretending to need an exorcism so I can get -- yes, that's right! -- so I can go to an exorcist and see if he's using gimmicks or psychological tricks to try to convince someone that they're possessed.
Sometimes that means I'm going undercover in a fringe group which I report on for a podcast that I co-host.
And I've done over 70 investigations like this with my co-host, Ross.
I would love to tell you that nine times out of 10, science wins, saves the day, it's all explained.
That's not true.
The truth is, 10 times out of 10, science wins, it saves the day.
(Applause) And that doesn't mean there's no such thing as a mystery.
Of course there are mysteries, but a mystery is a mystery.
It is not a ghost.
Now, I believe there are two kinds of truth, and it's taken me a while to get to this place, but I think this is right, so hear me out.
I think there is outer truth and there's inner truth.
So if you say to me, "There was a man named Jesus and he once existed," that's outer truth, right?
And we can go and look at the historical record.
We can determine whether that seems to be true.
And I would argue, it does seem to be true.
If you say, "Jesus rose from the dead," -- ooh, trickier.
(Laughter) I would say that's an outer-truth claim, because he physically rose or he didn't.
I'm not going to get into whether he rose or he didn't, but I would say that's an outer-truth claim.
It happened or it didn't happen.
But if you say, "I don't care whether he rose from the dead.
It's symbolically important to me, and that metaphor is so meaningful, so purposeful to me, and I'm not going to try to persuade you of it," now you've moved it from outer truth to inner truth, from science to art.
And I think we have a tendency to not be clear about this, to try to move our inner truths to outer truths, or to not be fair about it to each other, and when people are telling us their inner truths, to try to make them defend them by outer-truth standards.
So I'm talking here about outer truth, about objective things.
And there was an objective reality in my haunted house, right?
Now that I've told you about the gas leak, I doubt a single person here would be like, "I still think there was a ghost, too" -- (Laughter) because as soon as we have these scientific explanations, we know to give up the ghost.
We use these things as stopgaps for things that we can't explain.
We don't believe them because of evidence; we believe them because of a lack of evidence.
So there is a group in Los Angeles called the Independent Investigations Group, or the IIG, and they do great work.
They'll give a $10,000 prize to anyone who can show, under scientific conditions, that they have a paranormal ability.
No one's done it yet, but they've had a couple people who claim that they were clairaudients, which means that they can hear voices either from the great beyond or they can read minds.
And they had one person who was very sincere, who believed that he could read minds.
So they set up a test with him, and this is the way it always works.
The group says, "OK, we have a protocol, we have a way to scientifically test this.
Do you agree with it?"
The person says yes.
Then they test it.
It's very important that both sides agree.
They did that, they tested him.
They said, "OK, you know what?
You weren't able to predict what Lisa was thinking.
It matched up about the same as chance.
Looks like you don't have the power."
And that gave them the opportunity to compassionately sit down with him and have a very difficult discussion, which basically amounted to, "Hey, we know you're sincere, and what that means is, you do hear something in your head."
And that guy got to make the very difficult decision, but really the life-changing decision about whether to go get help.
We're actually helping people to make these connections that maybe before seemed like otherworldly explanations, help draw us into reality and maybe change our lives for the better.
Now, on the other hand, maybe one time it'll turn out to be true.
Maybe we'll find out there are ghosts, and holy shit, it will be the best thing!
And every time I do one of these investigations, I still get so excited, and I'm like 75 into them, and still I swear on number 76, I'm going to be like, "This is the one!"
(Laughter) Maybe I'm just eternally optimistic, but I hope I never lose this hope, and I invite you to take this same attitude when people share their outer beliefs with you.
When talking about testable claims, respect them enough to ask these good questions.
Challenge and see how you can examine them together, because there's this idea that you can't respect a belief and still challenge it, but that's not true.
When we jiggle the lock, when we test the claim, we're saying, OK, I respect you, I'm listening to what you're saying, I'm going to test it out with you.
We've all had that experience where you're telling someone something, and they're like, "Oh, that's really interesting, yeah," you know you're being had.
But when someone says, "Really?
Huh.
Sounds a little sketchy to me, but I'm listening," you at least know you're being engaged and respected.
And that's the kind of attitude we should have with these claims.
That's showing someone that you care what they're saying.
That's respect.
Now, yes, most of these searches will come up empty, but that's how all of science works.
Every cure for cancer so far has not panned out, but we don't stop looking, for two reasons.
Because number one, the answer matters.
Whether it's looking at the afterlife or the paranormal or the cure for cancer, it all amounts to the same question: How long will we be here?
And two, because looking for the truth, being open-minded, and being willing to be wrong and to change your whole worldview is awe-inspiring.
I still get excited at ghost stories every single time.
I still consider that every group I join might be right, and I hope I never lose that hope.
Let's all never lose that hope, because searching for what's out there helps us understand what's in here.
And also, please have a carbon monoxide detector in your home.
Thank you.
(Applause)