Nature versus nurture: it’s one of the oldest debates out there. How much of our personality are we born with, and how much develops in response to our experiences? Modern genetics is making it possible to examine these kinds of questions in ever greater detail, and one Harvard researcher is finding genes at work in complex behaviors.
Take, for example, the burrows built by wild deer mice. One species digs a simple burrow that looks kind of like a sock, with an entrance tunnel and a nest chamber. A sister species makes burrows that are ten times as long, and more complicated, with a secondary escape tunnel. By cross-breeding the two species in the lab, researchers have found four regions of DNA associated with those differences, and they're homing in on the genes responsible.
"It's not that the mice that dig these bigger burrows are more physically fit, or more active, or have bigger feet or longer tails," explains Hopi Hoekstra, Alexander Agassiz Professor of Zoology at Harvard University and the lead investigator on the deer mice studies. "It really seems like they're more motivated to dig."
Although humans don't generally dig burrows, we do manifest varying levels of motivation. And the burrowing motivation of deer mice is interesting, because it's not a general ambition. Mice that dig long, intricate burrows don't run more or do more of other activities. They're not Type A across the board. They're just driven to build great burrows.
"Once we start to understand how that neural circuitry evolves, we could really start to think about human behaviors," says Hoekstra. "What if we could design a drug that could change your motivation for certain tasks, like studying or exercising, but not other tasks, like watching TV or eating?"
Burrowing motivation isn't the only behavior Hoekstra's group is investigating. The same sister species show very different mating and parenting behavior, with one being monogamous and the other promiscuous. Males of the monogamous species also share more in nesting duties. Understanding the genetics underlying those differences would not only be interesting from an ecological perspective, it would likely spark a lot of interest among humans.
Of course, the next question is, if we know what genes control motivation or monogamy, could we reprogram people's genes to suit social ideals? An emerging gene editing technology, known as CRISPR, has raised the possibility of altering human embryos in a heritable way. Hoekstra's group is excited by the potential of using CRISPRto modify mice for research purposes, but acknowledges that application to humans is a different - and altogether trickier - situation.
"There are clearly ethical issues that need to be addressed," says Hoekstra, "but I don't think that should stop our quest to understand the genes that are involved in behavior because of this possibility that someday, down the road, this will be used for purposes we're not comfortable with."