Ted talks : Abigail Marsh - Why some people are more altruistic than others ?

I was a bit lost in the impressive variety of topics in this website ! But this title make me curious..
I really wanted to know if some people can have an explanation for altruism. So I will start by resume the video and then I will shortly give my point of view.
So basically this women explains that she was saved by a complete stranger during a car accident, the man crossed the traffic to rescue her, he puts his life in danger for this stranger. He saved her, makes sure she was ok, and went back to his life without even saying his name. That's a pretty impressive story and I totally understand why Abigail starts to questioning the altruism.
She's starting her topic lighting the notion of altruism, someone who cares more for others, someone with a lot of empathy and so on. Then she brings the question : why some people are more altruistic than others ?
That's in my sens an pretty interesting question. And her research begin with an study of psychopaths, who are basically the opposite of extreme altruists persons. Someone who can't not think about others feeling of fear, and with her study she finds out that there is a specific area into human brain which recognize fear (anxiety, ...) expressions on somebody's face. And to resume this area is smaller than the average for psychopaths and bigger for extreme altruists persons, she takes the example of people who gave a kidney to an complete stranger that they never meet (I recognize.. That's a really altruistic way of behave). So until that it's a kind clear explanation, you agree or not, but it's still clear. But after that I kind of loose the purpose.. She explains that's there is no center for extremes altruists, they don't based themselves on close relationship, everybody is the same, they are humble, they don't think they are unique and so on... She finish by saying that more we evolve more altruist we are, towards people and toward animals. That's great, that's sounds amazing ! BUT she doesn't explain it, she doesn't give any arguments for this second part.

So I find it interesting BUT I disagree ! This is too smooth... She doesn't put any social, educational variables... For her is just an area in the brain. What does it mean ? I am not deterministic. I don't think every thing is write in science. For me genetic and sciences, play a role but this is not the only variables. All the educational part, the social part with the new relationships, play in my sens also a big role.  

Nice website John !

Good choice Pauline and good review ! (I so much hesitated to choose this Ted talk...)

Thanks Laurine ! I am going to read yours to see if you hesitation was worth it ! ^^

So I look forward to your opinion!