Why apes started to contemplate and become altruistic?
I think this is a difficult question all around, which is why its a little uncomfortable for some to be entertaining questions which are often seemingly metaphysical in nature.

I think also that it is true that biology and neuroscience will have a big impact on the question, its also fair to say that the jury is still out on this question. 

The genetic anthropologist Svante Paabo is one of the most engaging researchers in this question.  He started out studying the difference between the human gene sequences and the chimpanzee to try to suss out the specific genes which might be be responsible for out social selves.  So from this point of view, it might be that intelligence started at most about the time of human chimp divergence, 8-25 million years ago.   

Finding the specific genetic structures that convey our unique cognitive or social abilities would certainly pinpoint that time much more accurately.  There is just 1-4% difference between the chimp and human genome sequences (depending on how you calculate it), but even 1% of a 5 Gb genome is a lot of differences and no intelligent mutant chimp has been found (that they've told us about!) .  

Since then, a lot of interest has focused on assembling a complete Neanderthal genome sequence.  Since Neanderthals diverged from humans about 500k years ago, and there's plenty of evidence that they were intelligent, comparing the three genomes (human chimp and neanderthal) would help pinpoint the specific genetic elements which are distinctly human.  

If it is a mutation or set of mutations as the current thinking implies, there is a good chance that it is a combination of strong selection and accident.  Its true that cooperation is often enjoys a strong selective advantage, but it doesn't make you smart or hospitable.  When we talk in biology we don't say altruism, we say cooperation.  If such cooperation happened only because of selection, we would see such behavior in other primates.  So if we see this, I would lay odds to look for a rather complicated story...

Another interesting person to read is anthropologist Terrence Deacon, who is trying to understanding the terms with which we define intelligence.  About ten years ago there were actually experiments that showed that chimpanzee some strong candidate intelligence genes related to cognition could be put into people (who needed gene therapy because they had lost cognitive function) and restore that function.  Apologies, this is anecdotal - i saw him give a great talk, but he's moved on a bit and can't find the references.  

This is important I think because the fundamental definitions of human intelligence have failed over the years, from the old chestnut of using tools, to a recognition of mortality, to awareness, animals have surprised us, particularly primates.   I wonder whether we will be able to confirm these vital factors until we get a monkey asking for the keys to the car so that they can go get some pizza.