Biology and Rational Choice

These are exciting times for those interested in the connection of biology to behavior. Consider the following findings that were reported in the first half of 2005 alone. Sexual foreplay for fruit flies is fairly predictable. A male first approaches a waiting female, bumps or taps her with his leg, rubs his wings in such a way as to make music, and then begins to lick her. The remarkable recent discovery is that when a single " male " gene is artificially inserted into the genome of a female fruit fly the female performs the precise ritual described above even though in nature females never act in this fashion. For their part, when males receive the female version of the gene they become both more passive and more sexually interested in males (Stockinger et al., 2005). That a single gene can so clearly induce such a broad range of different behaviors, from leg-tapping to wing-singing to body-licking, and can also affect preferences, in this case sexual preferences, is stunning. The fruit fly gene just described is a protein-coding gene. A large portion of the human genome is composed of non-protein-coding introns, nucleotide sequences that do not code for specific proteins and therefore have been given the undignified moniker of " junk DNA. " But recent discoveries indicate these lengthy portions of DNA will need to be taken more seriously. Scientists have found key features of the social behavior of voles (a small rodent) to be governed by repetitive microsatellites found in the introns (Hammock and Young, 2005). Voles with longer repetitive nucleotide sequences in a region near a gene that creates vasopressin receptors will produce more receptors and therefore will make better use of vasopressin, a hormone common in males and known to be relevant in pair bonding and offspring-tending behaviors. Though hereditary, these microsatellites are much more susceptible to mutations than are protein-coding genes so evolution can occur much more rapidly and, therefore, inter-as well as intra-species variation in behaviors influenced by repetitive microsatellites (presumably most social behavior) will be greater. Some evidence exists that human autistics, not known for their nurturing tendencies, have shorter repeat sequences than do neuro-typicals. The message is that not only do genes influence behavior but genomic material outside of the genes does too. Economist Ernst Fehr recently asked 178 undergraduates in Zurich to play a version of the trust game. Before the experiment …