For years the general public has been receiving optimistic predictions about how genetic research will change everyday life. In particular, there have been promises that all kinds of human behavior -- including overeating, belief in God, altruism, happiness, and depression -- can be linked to genes in a one-to-one correspondence, i.e., a single gene providing the key to a behavior. Hence the obesity gene or the gay gene, even the faith-in-God gene. But in his New York Times column a few days ago, David Brooks quotes a Hastings Center report that says, "behavioral genetics will never explain as much of human behavior as was once promised." The reason for this about-face, which has spread throughout the genetics community, has to do with the word "complexity." Human behavior isn't complex the way a game of chess is, or the way the wiring is in a computer, for example.
In those cases, the root of complexity is mathematical. There are so many possible moves in a single game of chess and so many crossover connections in a computer that simple actions become logarithmically multiplied. Human behavior isn't complex like that. We are complex because we are creative, emotional, unpredictable, uncertain, conflicted, confused, contradictory, impulsive, and personally unique. We are also constantly changing in response to the environment. It would seem obvious that these all-too-human traits cannot be ascribed to one gene or even a large group. An article this week in the journal Nature finds that it takes over a hundred coordinated genes to participate in the process of cell division, implicating an equal number of feedback loops, since cells operate by self-regulation, monitoring chemical reactions through opposite chemical reactions that keep both in balance. Cell division is simple compared to human behavior, and without knowing how the cell coordinates its activity, genetics is miles from figuring us out.
The deeper problem is that genetics insists on the wrong kind of complexity, the mathematical kind, in order to make progress. In another Nature article, researchers found that rats will perform not simply for rewards but for cues that remind them of those rewards, which the team terms cues for happiness. Human beings do the same thing. Seeing a can of Coke -- if you happen to like Coke -- will cause you to reach for it even though you haven't tasted it yet. But the researchers are stumped, in terms of brain response, by perverse behavior like drug addiction, which causes addicts to reach for their drug of choice even though the outcome will be unhappy. If cues produce happy and unhappy responses both, no clear brain function can be found for happiness. Again, one is facing a materialist fallacy, for it's not the brain that makes people happy or unhappy but a complex relationship that involves both feelings, often at the same time, as we live our lives. Perverse behavior is at once confused, conflicted, compulsive, influenced by memory, and tied to self esteem. So are bad marriages and dead-end jobs: people stay in them not for happiness but for reasons that bounce off each other and interweave in a tangle. Rats aren't a suitable model for our inner world and its mysterious ways.
In theoretical terms, genetics will predictably proceed in the same direction it is going. The mathematical model of complexity won't change. How could it? To truly understand human behavior, you have to turn inward, and subjectivity remains anathema to science's credo of detached objective observation. But since by definition consciousness can only be explored by consciousness, it has to be a subjective exploration. Any objective understanding of consciousness can only be inferential. On a practical basis, however, genetics is at a crossroads. In the same week that human trials for a potential AIDS vaccine had to be abandoned, the complex behavior of a retrovirus has defeated two decades of research, making one wonder exactly when those vaunted promises of a new age in medicine based on genetic breakthroughs are going to produce results.