Michael,

The reason I believe the formation of corneas is genetically determined -- even though there have been no studies to identify the relevant genes -- is the same as why I believe that unexplained perturbations in the orbit of astronomical objects are due to the gravitational effect of unseen companions; namely that the general theory that morphology is genetically determined (and that orbits are gravitationally determined) has no serious rivals.

However when it comes to explaining human behaviour the situation is quite different. The difference is that there exists neither a known explanation for how genes shape human behaviour, nor is there a single unambiguous prospective study showing the existence of a correlation between genetic and behavioural variations, such as "mental illnesses" or non-pathological intellectual or psychological attributes.

Therefore the belief that genes determine human behaviour is predicated entirely on the analogy with biological attributes that are known to be genetically determined (including the behaviour of lower animals). But the validity of this analogy is suspect for the same reason as would be the dogma that because computers are just machines therefore variations in their "behaviour" must be determined by variations in their hardware design.

It is only in the context of this tendentious analogy that the alleged evidence supporting the genetic causation of variations in human behaviour seems at all credible. By the normal standards of science the evidence is astonishingly poor. The fact that the academic community seems oblivious to this state of affairs just shows that we are dealing with a scientistic dogma rather than a scientific theory.

Seen in this light, and pending a good prospective study that demonstrates the existence of a genes-to-human-behaviour correlation, I think scepticism about genetic explanations of human behaviour is entirely justified.