Interesting reading.
The fact that altruism is pleasurable isn't a bit surprise.
I think that evolutionary game theory can be used to show why such a characteristic would be favourable for darwinian selection.

I think that the bit on the philosophical consequences was a bit naff though.

I had a discussion about this in biology class once. My teacher explained how there is no selfless act, since everything that you do ultimately rewards you. For example, by giving help and charity to others through your own wealth, you usually feel good about yourself. And others will be thankfull, giving you praise and attention. You will feel good about this because that's how the moral system in our culture works. If it was cultural to beat everyone who was weak, you would probably feel good about that too.

Except that what was culturally 'right' would necessarily be dictated by what makes you feel good as opposed to the other way around which is what this wording suggests. If it made us feel good because it was culturally acceptable then evolution would have no original basis by which to select for the trait of altruism. We do feel good because others in the culture reward us with praise for doing 'good', but their praising us is also dependent on the fact that doing good makes you feel good independent of praise and praising do-gooders is a 'good' thing to do that elicits the naturally selected for good feeling.

In this scenario acts that negatively affect individual happiness have little to no chance of becoming socially accepted as they will not produce the naturally selected feel good response within the individual.

Did that make sense to anyone but me?

It would seem that humans do innately benefit from generosity, as generosity amongst members of the group is often an important means of survival of a healthy breeding population. I would not say that cultures shape the evolution of such a response as much as that the need to live in societal groups has selected for the response and cultures are shaped by such a response.

Nope, that's group selection, not natural selection. Although there might be a slight evolutionary pressure in that direction, groups and societies are too amorphous to select for altruism.

What we need to do is look at it from a gene's point of view. So here we have a gene that says "I will reward you will endocrines if you help another". In early human societies, this gene would benifit greatley for some very important reasons.

 firstly, in very small human groups (as our ancestors had millions of years ago) there is a huge statistical probability that everyone you meet is a close relative. So a gene that rewarded you for helping everyone you met would benifit, because that same gene is likely to be in the people you help.

 Over time, this gene would spread throughout the population, because people who helped everyone else and were generous would benifit more copies of the altruism gene than a gene for selfishness. (A selfish gene, you see, would only potentially beinifit one copy of the gene, and wouldn't have the potential to spread as quickly)

 It is only now, that we live in large cities and are connected with everyone in the world that this gene begins to "misfire". We are wired to love and help everyone because we evolved for a small group or villiage, where our actions would likely benifit our own genes.

 This is not a bad thing though. One of the odd and wonderful charachteristics of evolution are the unintended side effects. Those effects can be either positive or negative, but in this case they are immensley benificial.

EDIT: this is in response to trafio.

EDIT2: On the other hand, there is a terrible negative side effect along this same vein. Somewhere along the line another gene mutated its way into the altruism gene and added something along the lines of "help everyone, but help people who look like you more than others. If the person does not look anything like you, don't be very nice at all". This would have been useful to the altruism gene because it increased the likelyhood that the gene would give help to another individual containing the same gene (since you are likely to look like your familiy members).

Unfortunatley this has misfired into widespread racism in modern times.