J. B. S. Haldane (1892-1964), the British geneticist and evolutionary biologist, was once asked whether he would be willing to die to save his brother, to which he famously retorted "No, but I would save two brothers or eight cousins." Since individuals share on average half of their genes with their siblings and one-eighth with their first cousins, Haldane's response corresponds to the "genetic" break-even point. Haldane's quip preempted the eventual work of William Hamilton on kin selection (1964) namely the idea that an organism can extend its genes by investing in those individuals who are biologically related to it. Evolutionary psychologists have explored a wide range of settings wherein such kin-based effects occur including patterns of bequeathments and bereavement, life and death decisions, prosocial behavior, and family caregiving (e.g., differential investments in biological versus stepchildren, or in siblings versus half-siblings).
In a few days, families all over the world will celebrate perhaps the most important of all Christmas rituals namely the exchange of gifts. Up to 40% of some retailers' yearly sales occur during holidays, a large chunk of which involves the purchase of gifts (Valentine's Day, Mother's Day, Father's Day, and Christmas). In addition to its economic importance, the gift giving ritual has broad social and anthropological implications, and is generally thought to be a human universal.
Does kin selection manifest itself within the gift giving ritual? Tripat Gill and I published a paper in Psychology & Marketing wherein we explored how individuals allocate their gift giving budgets to various prospective recipients (e.g., mates, family members, and friends). We theorized and found that genetic relatedness between givers and recipients was positively correlated to the expected gift expenditures. That said, individuals stated that they would spend the most money on their mates (i.e., more so than on their closest relatives), and that they would spend more on their closest friend as compared to a more distant kin (e.g., second cousins). These findings suggest that the gift giving ritual serves multiple Darwinian objectives including reproduction (gifts to one's mate), kin selection (gifts to one's kin), and reciprocity (gifts to close friends). Furthermore, in this particular context, the Darwinian pursuits were hierarchically ordered in terms of their importance. Not surprisingly, given that humans are a sexually reproducing species with high bi-parental investment, gifts to mates took the crown.
By the way, I do not wish to imply that gifts are strictly gauged in terms of their monetary value. Women are particularly impressed with thoughtful gifts from their significant others. Recall Jerry Seinfeld's faux pas when he had offered Elaine a wad of cash ($182 to be exact) as a birthday gift subsequent to having rekindled a romantic relationship with her. Such errors especially early in a relationship can result in a Darwinian cul-de-sac.
As you rush out for your last minute Christmas shopping, remember that both Santa Claus and Charles Darwin are expecting you to allocate your gift-giving expenditures judiciously! Ciao for now.