Friday, 4 July 2014

Wanted: human trait inheritance breakdown

Those tracking the inheritance of traits have tended historically to consider what proportion of the variance in a trait is explained by "genetic" factors - with the rest being explained by "the environment" - and chance fluctuations.

The figure differs according to what trait is being investigated, but an average figure of around 50% is often a reasonable guess for the proportion of the variance in a trait is explained by human DNA genes.

The concept of "heritability" is used to describe this.

However, a basic question in cultural evolution is what proportion of the variance in traits is explained by cultural inheritance. Alas, this question seems to have rarely been addressed.

Ideally, we would like a breakdown for a wide range of traits: human DNA genes, DNA genes of parasites and symbionts, cultural transmission, other environmental factors and chance.

Part of the problem is the very idea of "heritability" itself. The concept shoehorns the factors involved in development into 'genes' and 'the environment'. However, in the context of cultural evolution, this dichotomy is basically a naive and unhelpful classification scheme. It's the kind of classification that someone totally ignorant of cultural and environmental inheritance might come up with.

It would be better to split trait variances into inherited and non-inherited components - and then sub-classify the inherited components according to how the inheritance takes place - via host genes, symbiont genes, cultural transmission or environmental inheritance.

It's especially important to know what factors can influence a trait if you want to influence that trait. We do know some things about this topic - but mostly the basic science in this area appears to have been neglected.

One of the reasons why I want to know is because I want to quantify how significant cultural inheritance is - compared to DNA genes and to other forms of environmental inheritance.

1 comment:

  1. Split between DNA and cultural inheritance is an interesting problem and is I believe is the content of the Dual Inheritance Theory. The position I have come to with cultural inheritance is that generally DNA provides the physical machinery required for the trait while cultural inheritance largely provides the trait itself. For example with language DNA provides the requisite neural processing, larnyx etc. while cultural inheritance provides the language itself.

    This basic dichotomy may explain the vast majority of the variation over the worlds languages as due to cultural inheritance but the issue may become more murky if we want to understand say the variance in vocabulary within the family of a single language. My guess here is that this variance would involve both DNA (e.g. neural abilities) and cultural inheritance (e.g. exposure to a large vocabulary) in more equal proportions.