Theories of inheritance in the nineteenth and twentieth centuries : The role of historiographical constraints on contemporary scientific research, with particular emphasis on the role of "Weismann's Barrier" in Darwinian and Neo-Darwinian debates
Dr EJ Steele (external supervisor)
The focus of the thesis is the changing meanings of the concept of the ‘inheritance of acquired characteristics’ through the work of Lamarck, Darwin, Wallace, Weismann and Romanes in the late 19th to early 20th centuries and the relation of this to the recent published views, opinions or arguments of, amongst others, Steele and Dawkins. It offers a philosophical analysis of the historiography of the relevant scientific disciplines in order to interrogate the contemporary Darwinian, Neo-Darwinian, Neo-Lamarckian debate.
Experimentation to disprove the inheritance of acquired characteristics all too often took ‘characteristics’ to imply mutilations, or socially acquired behaviour, and ‘acquired’ to refer to the infliction of mutilations or to learnt behaviour. However, if we take ‘characteristic’ as referring to genetic information, with inheritance occurring ‘through the genetic apparatus’, and its ‘acquisition’ to be a matter of what comes from outside the parent organism, then the well documented evidence that ‘inheritance of acquired characteristics’ occurs in the plant (plants have the ability to genetically transfer a somatic, acquired, mutation) and bacterial kingdoms (in the form of horizontal gene transfer) becomes both logically possible and plausible. These forms of both vertical and horizontal gene transfer are not generally understood to represent a form of inheritance of acquired characteristics; but they clearly fit precisely that theorization. Thus we need to revisit ‘Weismann’s barrier’ with a view to offering an account of the differentiation between germ line and soma cells which is not distorted by its alleged implications.
Wallace suggested that Weismann’s work, along with Galton’s, should be ‘considered (if finally established) the most important contribution to the evolution theory since the appearance of the Origin of Species’. This assertion, made by a selectionist with a vested interest in establishing wider acknowledgement of Weismann’s work on heredity, is echoed throughout the historiography of Darwinism. Maynard-Smith highlights the link between Weismann’s Barrier and Crick’s outline of the central dogma of molecular biology - a link emphasised by Dawkins, who, in dismissing the inheritance of acquired characteristics, claims to be a Neo-Weismannist. However, recent research on germ-plasm variation has suggested that ‘Weismann was not a Weismannian’. Further confusion about ‘Weismann’s Barrier’ arises from the debates between Darwin, Weismann and Galton concerning pangenesis: the assumption that Weismann discounted the inheritance of acquired characteristics in all life forms is mistaken. Pangenesis, according to Darwin, referred mainly to vegetative or fissiparous reproduction; Weismann in fact does not rule out the transmission of acquired characteristics in these cases.
I argue that the historiographical precedent for the wholly selectionist, Ultra-Darwinian, definition of ‘Weismannism’ and ‘Darwinism’ was set by, amongst others, the historical accounts of ‘Darwinism’ by Romanes and by Wallace himself. Furthermore, in recent debates between advocates of the ‘Lamarckian’ and Weismannist’ positions - for example Steele vs. Dawkins - the conceptualisations of ‘inheritance of acquired characteristics’ are related to their different disciplinary perspectives. This disciplinary divide is further compounded by the experimental nature of Steele et al who are directly testing the scientific validity of 'Weismann's Barrier' in higher animals while Dawkin’s work is entirely theoretical. It is the semantic barriers between these disciplines, coupled with attendant historical and philosophical constraints, that has led to their respective perception of the current research data as conflicted. The use of an undifferentiated terminology (‘inheritance of acquired characteristics’) to represent what are in fact different outcomes in research can thus result in what looks like a paradigmatic disagreement between two opposing groups of scientists, something that would normally be due to the existence of anomalous data. To the extent that both sides in the Steele/Neo-Darwinian debate accept a conception of the inheritance of acquired characteristics which is far from being the only one possible, they partly misunderstand one another and, indeed, themselves.