James Maclaurin

Molecular Weismannism is the claim that: “In the development of an individual, DNA causes the production both of DNA (genetic material) and of protein (somatic material). The reverse process never occurs. Protein is never a cause of DNA”. This principle underpins both the idea that genes are the objects upon which natural selection operates and the idea that traits can be divided into those that are genetic and those that are not. Recent work in developmental biology and in philosophy of biology argues that an acceptance of Molecular Weismannism requires the tacit assumption that genetic causes are different in kind from other developmental causes. They argue that if this assumption proves to be unwarranted then we should abandon, not just gene selectionism and gene centred functional solutions to the units of selection problem, but also the very notion that there is any such thing as a “genetic trait”. A group of possible causal distinctions (proximity, ultimacy and specificity) are explored and found wanting. It is argued that an extended version of information theory, while not strong enough to support Molecular Weismannism, will support both the claim that traits can be divided into those that are genetic and those that are not as well as the claim that there is good reason to privilege genetic causes within evolutionary and developmental explanations. The outcome of this for the units of selection debate is explored.