Published as Appendix 4 of The Way: An Ecological Worldview, originally published in 1992.
This text is taken from the revised and enlarged edition, University of Georgia Press, Athens, Georgia, 1998.
Mainstream science sees evolutionary change as exclusively the result of changes affecting the genes of individual living things. No other processes – neither morphogenesis nor the development of a child into an adult, nor our physiological, nor our behavioural experience – are regarded as affecting the genetic material in any way. These processes are seen as external to evolution and hence unable to play an evolutionary role.
Darwin never said this. For him, natural selection from random mutations (or random variations as he referred to them) was not the only mechanism of evolution – only the principal one. Indeed, towards the end of his life, he actually accepted Lamarck’s ideas on the inheritance of acquired characteristics in order to dispose of Fleeming Jenkin’s criticism.
It was not Darwin but Weismann who formulated the preposterous dogma that natural selection is the only mechanism of evolution, thereby denying that behaviour could affect evolution through the inheritance of ‘acquired characteristics’. This thesis, another of science’s gratuitous dogmas, is based on no serious theoretical or ecological considerations.
Weismann’s main argument for it is that he could not conceive of a mechanism whereby acquired characteristics could be translated into the language of the gene, and it was for this reason alone that he insisted – as P. Wintrebert points out – that all biologists had to agree that it did not exist.
It can be argued that Weismann proved his point experimentally – but his experiments were little more than a farce. He cut off the tails of rats, let them breed, repeated the experience on their progeny and went on doing this on 22 generations of these animals. The fact that a tail-less breed of rats did not arise he held to be proof that acquired characteristics were not transmitted.
However, as Wintrebert notes, Lamarck never suggested that living things passed on their mutilations to their progeny but only the characteristics that they developed as a result of their own efforts. Indeed, the rats, as Arthur Koestler put it, were no more likely to transmit their mutilated tails than a mutilated man is likely to transmit his wooden leg. 
Such experiments are, in any case, deeply flawed for another reason. Though the genetic material is indeed plastic – contrary to what we are told – it is only slightly so. As J. B. S. Haldane noted, it is always possible that such experiments will fail, because the effects of acquired characters may not become apparent at a rate that makes them observable, though they may be rapid enough to be significant in geological time. 
There are countless reasons why the genetic material in the genome cannot be isolated from the genes of the soma. To begin with, no life process can maintain its homeostasis without acquiring information concerning its relationship with its environment in order to monitor its actions and correct any divergences from the appropriate course on which it is set. The only possible sources of such information are morphogenesis and behaviour (ontogeny).
Secondly, genetic material is not external to a living system but part of it. The genes do not dictate epigenesis, which, as Commoner has shown so convincingly, can only be understood in terms of the interaction between the genetic material and the cytoplasm which forms its environment. Nor, for similar reasons, do the genes dictate evolution.
In addition, as Grassé points out, if we accept the Weismann-Crick thesis, how do we explain the creation of new genes?  The first living thing itself would have been endowed with all the genes which have made possible the evolution of plants and animals in their infinite variety. Since no information can have come from the outside, DNA must have been the unique source of information. This means, surely, attributing miraculous properties to this chemical substance, which is simply not a serious thing to do.
It has always been quite clear to serious students of evolution that there had to be a feedback between behaviour, ontogeny and evolution. In 1896 the American psychologist J. M. Baldwin published the famous article in which he described his principle of “functional and organic selection”. 
In adapting to its environment, Baldwin maintained, an organism can affect its congenital characteristics by “accommodating” them to new environmental conditions. These accommodations, he argued, can eventually become fixed genetically. Forty years later, Richard Goldschmidt suggested that information contained in the phenotype which is acquired by a living thing during the course of its life, can, in certain conditions, be “copied” by the genome and then become fixed genetically as a “phenocopy”. 
Waddington proposed an analogous mechanism that he referred to as “genetic assimilation”.  He saw organisms as being able to respond to stress by changing their behaviour and sometimes by bringing about corresponding structural changes. To do this, they must be able to defy the pressure on them to resist divergences from their pre-ordained course or constellation of chreods.
This can only mean affecting, in some way, the genes that control the stability or flexibility of these chreods and eventually – perhaps after a few generations – modifying them. Once this has happened, the altered phenotype can occur with or without the environmental stress, and it would then be said to have been “assimilated by the genotype.”
At the same time as Waddington developed the theory of genetic assimilation, the Russian theoretical biologist I. L. Schmalhausen worked out a slightly different way in which negative feedback could occur.  He referred to it as “stabilising selection”. Later, Piaget revived Goldschmidt’s phenocopy, which he modified considerably. The resulting mechanism is the most interesting, in that it diverges the most from the neo-Darwinian position, as the acquired changes are not seen to be the product of natural selection. 
In any case, recent experiments conducted by Cairns and others now seem to have established empirically that information flows in both directions. This means that mainstream scientists no longer have any argument for opposing the essential and inescapable principle that morphology, physiology and behaviour are integral parts of the evolutionary process, providing it with highly effective feedback mechanisms to ensure that it remain adaptive to changing environmental conditions, without sacrificing its stability or continuity.
|1.||Arthur Koestler, Janus – a Summing Up; p.197. Hutchinson, London, 1978.|
|2.||J. B. S. Haldane, Possible Worlds. London, 1940. Cit. Koestler ibid.; p.198.|
|3.||Pierre-P. Grassé, L’Evolution du Vivant; pp.374-379. Albin Michel, Paris, 1973.|
|4.||J. M. Baldwin, “A new factor in evolution”. American Naturalist, 1896; pp.354-451.|
|5.||Richard Goldschmidt, “Gen und Aussenergenschaft”. Vererbungslehre 69, 1935; pp.59-92.|
|6.||C. H. Waddington, The Evolution of an Evolutionist. Edinburgh University Press, Edinburgh, 1975; pp.59-62.|
|7.||Ivan Schmalhausen, Factors of Evolution: the Theory of Stabilizing Evolution. Blakiston (McGraw Hill), New York, 1949. Translated by Isadore Dordick; edited by Theodosius Dobzhansky. Cit Waddington, ibid.; p.75.|
|8.||Jean Piaget, Le Comportement, Moteur de l’Evolution. Gallimard, Paris, 1976.|