Almost fifteen years ago, in a book called “Chance, Development, and Aging,” the gerontologists Caleb Finch and Thomas Kirkwood described a truly elegant study of biology: a batch of roundworms, all genetically identical, raised on identical diets of agar. Despite having identical genetics and near-identical environments, some worms lived far longer than others. The lesson? The classical equation of “life = nature + nurture” had left out chance.
Of course, that was just worms. This week, a team of German researchers, led by Gerd Kempermann, built on a similar logic and announced in Science that they had raised forty inbred mice that were essentially genetically identical in a single complex environment, and used radio-frequency identification (RFID) implants to track every moment of their lives. Nobody could ever ethically run that sort of controlled experiment with humans, but Kempermann’s study provides convincing evidence that–in a fellow mammal with which we share a basic brain organization–neither genetic identity nor a shared environment is enough to guarantee a common fate. Different creatures, even from the same species, can grow up differently, and develop significantly different brains–even if their genomes are identical, and even if their environments are, too.
Because of the care with which Kempermann and his colleagues tracked the individual mice, the study provides considerable new insight into how we become who we are. It speaks to what the psychologist Sandra Scarr once called “niche-picking”: the idea that each individual develops a different set of talents, in order to carve out his or her own identity. Two people with initially slight differences might develop radically different skills, because they follow different paths. One child likes basketball, another painting; at first hardly anything distinguishes the two: both struggle to make baskets, and neither one can yet draw a credible house. But, from the outset, the first is slightly better at basketball, the second at art. Over time, the first child devotes herself to basketball, spends thousands of hours playing the game, and eventually becomes a professional athlete; the other applies herself equally to her chosen pursuit, and becomes a great artist. Tiny initial differences in talent, or simply in desire, become magnified over time. By tracking in detail the learning curves for forty individual mice, genetically identical and with essentially equal environmental opportunity, Kempermann and his colleagues show how the same kind of magnification can happen under carefully observed laboratory circumstances.