Chimpanzees (and humans) trade for biological "services."

{ Podcast this essay } Seeing this sign reminded me of an article I recently read. Chimpanzee society shares many striking resemblances to human society. Like us, Chimps form complex social bonds, and they do so with symbolic gestures, most notably by means of sharing of prized resources. For example, though chimps will rarely share the wild plant foods which they forage, for strategic social situations they will share prized foods, such as meat or pilfered, cultivated plant foods (from human crops) as a way of reinforcing social bonds and constructing new alliances.

Most of the sharing occurs when adult males make offers to females that are in the proper cycle for reproduction -- for reference, call such females who receive these goods "hotties". Exchanging food for increase of sexual access is certainly in the male's advantage, and may showcase his suitability to sire, given that he has the capability to acquire such goods. Hotties apparently find this a fairly good indicator of male reproductive health. This activity can generalize even beyond primates as an analysis of altruism:

Food sharing has important implications for the evolution of cooperation, offering a means to evaluate the ‘paradox’ of altruism, whereby a recipient gains fitness benefits at the expense of a donor. When individuals control a highly valued resource, they may opt to use that resource as a tool for social bargaining. Thus, even acts that appear altruistic may serve to ultimately enhance one’s own fitness.[1]

What is also interesting in this study is that the sharing of prized resources was not an immediate cost-benefit payoff: "Males shared crops with a maximally swollen female in 16% of sharing events, but were never observed mating with that female immediately after sharing." I would speculate that hotties would be far better off (in terms of expected reproductive benefits) waiting to see if the pattern could be (i.e. would be) maintained over time.

Diamonds (and of course other valued stones) have been assessed by women across history as attractive gifts. It is known that primitive humans were the first mineral collectors of such stones as chert, chalcedony, and obsidian. These were shaped into arrowheads and spear points for hunting. Later in pre-history, humans used turquoise, gold, silver, and copper in religious ceremonies, for spiritual enhancement, and protection from evil. I think a reasonable speculation would be that the symbols of such stone technology could stand for the hunting capability of the man who gave such a symbol to a desired hottie. Throwing a deer carcass at a hottie would not be practical, or perhaps desirable, but bequeathing a symbol (or an actual instance) of the technology that shows clear access to a desirable resource would be a very small step from the meat-sharing behaviors of chimpanzees. (Also, it could be that good hunting technology shows intelligence, and intelligence is what is actually strongly favored by women in modern mate selection.[2]) Modern jewelery exchange seemingly begins as an abstraction of just such a process about 100,000 years ago.[3]

I've been thinking about getting my wife a necklace for Christmas, but I don't want any more children. So perhaps I should just cease this whole line of thinking.

REFERENCES

[1] Hockings KJ, Humle T, Anderson JR, Biro D, Sousa C, et al. (2007) "Chimpanzees Share Forbidden Fruit." PLoS ONE (Accessed 11/22/2007)

[2] Ray Fisman "An Economist Goes to a Bar and solves the mysteries of dating" Slate Magazine 11/7/2007 (Accessed 11/22/2007)

[3] "Researchers Identify What May Be Oldest Known Jewelry" Voice of America 6/22/2006 (Accessed 11/22/2007)


O.