I haven't forgotten the importance of Amotz Zahavi's contribution to our understanding of evolution, which I only mentioned in passing earlier. Evolutionary concepts are fascinating when one realizes the powerful and wide ranging implications they have. Take for example Gould's paper "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" (1979) or Trivers paper "Parent-Offspring Conflict" (1974). To these add Zahavi's "Mate selection - a selection for a handicap" (1975).
Amotz Zahavi elaborates this theory even more in his book The Handicap Principle: a missing piece of Darwin's puzzle. Specifically in chapter 12 "Babblers, competition for prestige, and the evolution of altruism", he demonstrates that when an animal acts altruistically, it handicaps itself - assumes a risk or endures a sacrifice - not primarily to benefit its kin or social group but to increase its own prestige within the group and thus signal its status (and fitness) as a partner or rival. "Altruistic acts obviously demonstrate - and are perceived as demonstrating - the abilities of those who perform them." (p225)
What does this say about religion, which may be a handicap itself? Or Aristotle's virtue of magnanimity, or Guy Laliberté (known for throwing the best parties), or romantic overtures (whose goal is often copulation)? I think it sheds light on all of them.
It is interesting to note that the two competing theories explaining the origin of altruism are Zahavi's Handicap principle, and W. D. Hamilton's "kin selection" theory. It appears that Hamilton's theory is more popular among evolutionary biologists, although it is not without problems. The subject remains unresolved. Here is a video of Arabian babblers, and a lecture by Zahavi.