Natalie Angier in The New York Times:
We may denounce the hyper-consumerism of the Christmas season until we’re Hanukkah blue in the face, but much of our economy relies on the strength of the gift-giving impulse, and with good reason: The drive to exchange presents is ancient, transcultural and by no means limited to Homo sapiens. Researchers have found striking examples of gift-giving across the phyletic landscape, in insects, spiders, mollusks, birds and mammals. Many of these donations fall under the rubric of nuptial gifts, items or services offered up during the elaborate haggle of animal courtship to better the odds that one’s gametes will find purchase in the next generation. Hungry? Why don’t you go ahead and chew on the droplets oozing from my hind-leg spur while I just take a few moments to deposit a sperm packet in the neighborhood of your genitals?
Nuptial gifts can also be a gift for researchers, allowing them to precisely quantify a donor animal’s investment in mating and reproduction, and to track the subtleties of sexual competition and collusion by analyzing the chemical composition of a given bag of courtship swag. “This is an incredibly cool and important topic in sexual selection that we’re just beginning to explore,” said Sara M. Lewis, a professor of biology at Tufts University who has written extensively about nuptial gifts. “The bright side of nuptial gifts is, here’s a way that males can contribute things that are essential to his mate and to his future offspring. “On the other hand, the gifts can be a source of sexual conflict, a way of manipulating the female into doing what he wants,” she said. “So there is a lot of back and forth over evolutionary time.” Other researchers are studying how animals use gifts socially, to foster alliances or appease dominant members of the group. Grooming among primates is considered a form of gift-giving, and in most cases, it’s the subordinates who do the tick-picking: betas groom alphas, females groom males.