This correspondence on my article (Noble, 2015) is very welcome since it accepts the main point I made in relation to epigenetics and evolution. Williams and I therefore agree that ‘recent observations reveal multiple generations sharing the parent's environmentally induced phenotype, even in the absence of the original factor’. Where we disagree is whether this is incompatible with neo-Darwinism.
Those who formulated neo-Darwinism would not have accepted this. The central basis of the theory was established by Weismann (1892) in postulating the existence of the Weismann barrier that would make inheritance of environmentally induced variation impossible: ‘when these deviations only affect the soma, they give rise to temporary non-hereditary variations; but when they occur in the germ-plasm, they are transmitted to the next generation and cause corresponding hereditary variations in the body’. As Dawkins expressed it, genes are ‘sealed off from the outside world’ (Dawkins, 1976). Mayr (1982) and many other neo-Darwinists concur: ‘All of the directions, controls and constraints of the developmental machinery are laid down in the blueprint of the DNA genotype as instructions or potentialities’.
If we accept that environmentally induced phenotypes can be inherited, as recent observations abundantly show (Tollefsbol, 2014), then we have broken the Weismann barrier, because the germline is no longer isolated from the environment and the organism's response to it. We have also automatically broken the other neo-Darwinian assumption of random variation because phenotype changes can then guide inheritable variation. The honest response to this situation is to say that the central tenets of neo-Darwinism are no longer valid. We then return to a modern version of Darwinism. Darwin accepted the inheritance of acquired characteristics and formulated a hypothesis in his 1868 book The Variation of Animals and Plants under Domestication, his pangenesis theory of gemmules, which turns out to be not so far removed from what we have now found. His gemmules can be viewed as our inheritable epigenetic changes.
If, as the commentator seems to imply, we make neo-Darwinism so flexible as an idea that it can accept even those findings that the originators intended to be excluded by the theory it is then incumbent on modern neo-Darwinists to specify what would now falsify the theory. If nothing can do this then it is not a scientific theory.
Concerning Collins and Venter, I did not quote or refer to either of them in my article. I quoted an earlier version of the Nature Editorial, with which I entirely concur: ‘They began to see DNA as the “book of life”, which could be read like an instruction manual. It now seems that the genome might be less like a list of parts and more like the weather system, full of complicated feedbacks and interdependencies’. This is the reason why the gene-centric approach has failed to deliver its promises on health care (Joyner and Prendergast, 2014). The references to Collins and Venter are in a revised editorial, not in my article.
It is impossible to reply to all the points made. Further details are in the recording of a session on evolutionary biology at EB2015 (https://www.youtube.com/watch?v=A_q_bOWc8i0).
