Underappreciated epigenetics:
A recent article (Genetics Tells Tall Tales, Alla Katsnelso NATURE vol. 465 no. 7301 June 24, 2010 page 998) reports an article from NATURE GENEITCS that addresses the inheritability of complex traits. It turns out that height is 80 to 90 % inheritable but that the known genetic factors only account for about 5% of it. They call it the “missing heritability.” And it turns out that the phenomenon is found in many complex traits.
Of course two mechanisms come to my mind. One is that height is simply an example of general overall vigor. People are tall if everything is working just right, and everything except fertility is likely to work right if there is maximal genetic diversity. The less inbreeding among your ancestors for several generations back, the taller you will be. This is called “heterozygote advantage,” and nobody doubts it is real.
The other possibility is that the variation in complex traits is under epigenetic rather than genetic control. Or maybe both processes are at work.
At all events, neither is mentioned in the article. They simply conclude that we need to keep looking closer at those genes on the assumption that it has to be genetic because it is inherited, and perhaps it is just a matter of an enormous number of genes each with a small effect.
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