Executive Brain Function 99% Genetic?

Chris Chatham of Developing Intelligence reports on a recent twins study of "executive function" of the human brain.

Your ability to control thought and behavior relative to your peers - a set of capacities known as "executive functions" - is almost entirely genetic in origin, according to a new paper from Friedman et al. (newly in press at JEP:G.) Executive functions are highly correlated with IQ, but are thought to represent a more isolated and controlled measure of cognitive processing. Over 420 twins completed tests to measure fundamental components of these executive functions, and the results were analyzed in terms of how similar identical twins performed to one another relative to fraternal twins (all twins in the study were reared together). Astonishingly, the results show that the variance common to all executive functions is correlated roughly twice as much between identical twins as between fraternal twins - indicating that individual variance in executive function falls directly in line with what would be expected from a nearly perfectly heritable trait.

...Friedman et al. integrated measures of general intelligence ("g", estimated through the WAIS IQ test) and perceptual speed (essentially the speed with which subjects can complete very simple tasks) to show that the genetic contribution to executive function is not completely explained by genetic contributions to those more commonly-studied abilities. This is consistent with previous work showing that IQ is only moderately heritable (with 50-70% of variance explained due to genetic factors, far short of the 99% explained here).

Developing Intelligence

As Chris points out, the study did not rule out a significant contribution of environment to gene expression. Any attempt to do so should be viewed very skeptically.

Twins studies remain highly useful in the study of genetic differences contributing to mental attributes. Currently no other research tool even comes close in utility for that purpose.