Weismann Rules! OK? Epigenetics and the Lamarckian temptation

August Weismann rejected the inheritance of acquired characters on the grounds that changes to the soma cannot produce the kind of changes to the germ-plasm that would result in the altered character being transmitted to subsequent generations. His intended distinction, between germ-plasm and soma, was closer to the modern distinction between genotype and phenotype than to the modern distinction between germ cells and somatic cells. Recently, systems of epigenetic inheritance have been claimed to make possible the inheritance of acquired characters. I argue that the sense in which these claims are true does not challenge fundamental tenets of neo-Darwinism. Epigenetic inheritance expands the range of options available to genes but evolutionary adaptation remains the product of natural selection of random variation. In Evolution in four dimensions (EFD), Jablonka and Lamb present, what they believe is, a radical challenge to ‘‘the gene-centered version of neo-Darwinism that has dominated biological thought for the past 50 years’’ and to ‘‘the usual version of Darwin’s theory of evolution, which is that adaptation occurs through natural selection of chance genetic variations’’ (EFD, p. 1). Their challenge takes the form of evidence that there is more to heredity than genes; that some hereditary variations are nonrandom in origin; that some acquired information is inherited; and that evolutionary change can result from instruction as well as selection. The four dimensions of Jablonka and Lamb’s title are systems of genetic, epigenetic, behavioral, and symbolic inheritance. My comments will focus on the second dimension of epigenetic inheritance, because this is my area of expertise. The term Epigenetics had two independent origins in the twentieth century, but this dual origin has not been widely recognized and the two meanings have become conflated (Haig 2004). Waddington (1942a) used epigenetics to refer to the causal processes of development, with an emphasis on interactions among genes and between genes and the environment. Nanney (1958) used epigenetic to describe systems of cellular heredity that were not based on the DNA sequence. Epigenetic mechanisms, in the latter sense, can involve purposeful modifications to an organism’s own genetic material in response Biology and Philosophy (2007) 22:415–428 Springer 2006 DOI 10.1007/s10539-006-9033-y