I believe the law stated below almost follows from the observation that humans brains are complex machines: hence the DNA blueprint has many components, and variance is spread over these components :^)
However, note the evidence for discrete genetic modules of large effect in other species: Discrete genetic modules can control complex behavior (burrowing behavior in cute mouse in picture at bottom), As flies to wanton boys are we to the gods (discrete genetic controls on drosophila behavior).
THE FOURTH LAW OF BEHAVIOR GENETICS
Christopher F. Chabris, Union College
James J. Lee, University of Minnesota Twin Cities
David Cesarini, New York University
Daniel J. Benjamin, Cornell University and University of Southern California
David I. Laibson, Harvard University
Abstract
Behavior genetics is the study of the relationship between genetic variation and psychological traits. Turkheimer (2000) proposed “Three Laws of Behavior Genetics” based on empirical regularities observed in studies of twins and other kinships. On the basis of molecular studies that have measured DNA variation directly, we propose a Fourth Law of Behavior Genetics: “A typical human behavioral trait is associated with very many genetic variants, each of which accounts for a very small percentage of the behavioral variability.” This law explains several consistent patterns in the results of gene discovery studies, including the failure of candidate gene studies to robustly replicate, the need for genome-wide association studies (and why such studies have a much stronger replication record), and the crucial importance of extremely large samples in these endeavors. We review the evidence in favor of the Fourth Law and discuss its implications for the design and interpretation of gene-behavior research.
The influence of monoamine oxidase A on behavior did robustly replicate. According to Dorfman et al, MAOA had "one of the best supported GxE observations in the entire literature of psychiatric genetics." I once asked Chabris of his view on this subject. He declined to express an opinion because he said he wasn't familiar with the research, yet he and others repeatedly suggest that no individual genes are important for human behavior. MAOA science has been subjected to ham-fisted attempts to discredit it. First, people like Steven Pinker tried to claim that its commonality in Chinese people (based on a copy-and-paste error) disproved its influence. More recently, an extremely bad "meta-analysis" tried to disprove all candidate genes at once. It lumped MAOA studies on aggression in schizophrenics with studies on aggression in alcoholics, ignored studies on normals, and even ignored the control sample in one the studies it did include. A much better meta-analysis on MAOA came out at the same time and reached the opposite conclusion. Claiming a fourth "law" against important behavior genes invites mockery.
ReplyDeleteNote use of "typical" :-)
ReplyDelete“A typical human behavioral trait is associated with very many genetic variants, each of which accounts for a very small percentage of the behavioral variability.”