Wednesday, 13 April 2016

Thoughts on Heritability

Using Waddington's idea of canalisation. This is the related to the width of the canalisation - this is the maximum variation between a pure in bred low phenotype and a pure in bred high phenotype. This is the variance in that characteristic which is attributable to the genes.

This is going to be very hard to measure unless you do it for a genuine population. If you have a non representative sample then that will have its own variability and the variation in that characteristic will depend on the state of all the different end points you are starting from in a normal mating population carrying all of its history and variation. Think of dogs the dog population includes all the breeds but the variation within breeds is very low, the same with horses but with humans you have Usain Bolt and me to compare for our 100 metres performance.

The width of the canals is important as it shows the plasticity in response to environment. How far does it need to be pushed to get someone outside the normal bounds. The genes make the landscape and they do not determine the outcome except in pure bred lines where the canals are very narrow. 

High heritability could actually signify large canals and low determinism because we are very far from a pure bred line and everyone is close to the middle of a large canal. But it could also indicate low variation and a multi-modal population - mixing of species, comparing apples and oranges. Conversely low heritability measures would mean that there is low variation with very narrow canals and it is very strongly inherited.

The concept of heritability implies that you can have a pure bred line for a specific phenotypic characteristic and so that characteristic must be inheritable. So my reason for questioning the paper rejecting Haidt and heritability is that why would his classifications be capable of being bred for? Can I breed someone who believes in justice over everything? Can I breed someone who finds disgust in the unclean their biggest driving force? Can any of these higher human constructs be embedded into genes or are they more accurately modelled at the meme/cultural evolutionary level? This is what I meant by there being strong determinism - that you could breed for it and that the genes would determine the effect. 

My opinion is that they are at the cultural evolutionary level and only the very simplest of behaviours is canalised at the genetic level. This would be probably things like higher level reasoning, personal identity, desire to reproduce, desire for satisfaction etc. The advantage of the cultural/meme level is that it is NOT Darwinian. It develops during lifetimes and is directly passed on to the next generation. It is Lamarckian and not wasteful random exploration. It builds on what we already have and is rapidly modified. It is much faster than genetic evolution.