There's been a similar article on gnu.org for a long time: http://www.gnu.org/philosophy/motivation.html.

GNU people seem more interested in questioning whether we all really are (or should be) selfish/capitalistic. Ev.psych people just redefine self-interest to also include the pleasure of helping others. Personally I'm not sure either of these are sufficient answers.

I declined the offer of an ice cream cone one time as a little kid.

Ah, yes. But those children who were given nothing for their labors went on to use their pens as weapons to rob fat, rich, old 'evilutionary' psychiatrists and the corporations that they worked for, because the children realized they had no money to feed and shelter themselves or their growing families -- and no legitimate means of obtaining income because they'd spent their youth drawing silly circles on pieces of paper for delighted old men ....

Someone did that to me when I was kid. Big mistake. I started writing with the pen and haven't stopped so far.