The problem stems largely from the fallacy known as "regression to the mean" (RTM), which was first identified by Sir Francis Galton, a cousin of Charles Darwin, in the 19th century. It results from the fact that uncommonly large or small measurements are generally followed by more normal measurements simply because normal values are by definition far more common than extreme ones. In the Browns' experiment, when individuals are fostered from small to large colonies they will on average recruit to colonies that are statistically smaller than their foster colony because these are closer to the mean colony size and vice versa.
Danchin and Wagner actually found a second problem with the original data analysis. The so-called "spatial fallacy" was discovered by Arie van Noorwijk in 1984 and occurs when the set of potential dispersal sites differs among individuals according to where they were born. Together the two fallacies can account for the experiment's results, even in the absence of an inherited component of the selection of colony size.
A question of design
The latest calculations are important for two reasons. First, they call the original conclusions into question and should thus encourage researchers to reconsider the role of genetic factors in certain behavioural decisions. Secondly, they sound a clear warning to all those working in behavioural science. As Wagner says, "The biggest shock is that the very experimental design that is widely used to control for all extraneous effects actually creates the RTM f
|Contact: Richard Wagner|
University of Veterinary Medicine -- Vienna