Monday, 9 February 2015

The evolutionary gene

The idea of an evolutionary gene dates back at least to G.C. Williams (1966) - who said:

In this book I use the term gene to mean 'that which segregates and recombines with appreciable frequency'


In evolutionary theory, a gene could be defined as any hereditary information for which there is a favorable or unfavorable selection bias equal to several or many times the rate of endogenous change
Williams clearly defined genes in information-theoretic terms, saying:

The gene is a package of information, not an object.


A gene is not a DNA molecule; it is the transcribable information coded by the molecule
I think that the idea of a gene as consisting of heritable information has stood the test of time. However, the idea that genes are defined in terms of their frequencies seems more suspect. Terms like "appreciable frequency" and "several or many times" lack scientific rigor. Presumably they were used in order to prevent entities which are too complex from having 'gene' status. However, there seems to be no compelling reason to build them into our conception of a gene. Similarly, invoking "selection bias" seems to define unfairly neutral genes out of existence. Again, this is unnecessary - and can be simply avoided.

Instead of Williams mutually-contradictory definitions, I have proposed defining a gene as:

a small section of heritable information
The definition makes no mention of DNA, nucleic acids - or of living systems. It is a fairly general term - and generality is usually a virtue in science.

Richard Dawkins was another early pioneer of informational genetics. Although he initially used the "gene" concept he eventually substituted "replicator" - suggesting that this concept was more clearly substrate neutral. However, the resulting replicator revolution has not gone very well - and many years later there's no science of replicators that can compete with genetics. I don't think we need two sciences of heredity. It seems better to improve the existing field of genetics than to attempt to create a new scientific field that competes directly with it.

It is worth noting that the common definition of evolution in terms of changes in gene frequencies depends critically on the use of the evolutionary gene. Without the evolutionary gene, the idea that evolution consists of changes in gene frequencies would exclude cultural and environmental inheritance - and would make no sense.

In modern times it has become fashionable to claim that evolution is too "gene-centric" - and pays too little attention to other forms of inheritance. For example, here is Robert Kadar:

We now know genes are sufficient but not necessary for natural selection because 1) genes are the likely product of selection and 2) genes are only one source of heredity among others. The gene-centric view of evolution is crumbling!
Such sentiments make no sense in the context of the evolutionary gene. Genes are the units of inheritance in evolution. All inheritance is mediated by genes - just as all messages can be represented by bits. Defining the term "gene" so that it is stupid and useless is not good scientific practice.

Another group of biologists study what they call "epigenetic inheritance". Again, this whole concept makes no sense in the light of the evolutionary gene. Inheritance is genetic - by definition. The term "epigenetic inheritance" is an oxymoron.


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