Historical revisionism and the inheritance theories of Darwin and Weismann.

Abstract

In a comment on our paper (Niklas and Kutschera 2014), Liu and Zhi (2015) propose that Charles Darwin (1802–1882) and AugustWeismann (1834–1914) understood the mechanism of epigenetic inheritance in part because each accepted the notion that external factors could modify the development, and thus the phenotype of cells, tissues, and entire organisms. This proposition is a matter of historical interpretation. The authors further propose that recent studies reveal that environmental factors can induce the phenotypic changes that are passed on for one or more generations in a manner that corresponds to the views of Darwin and Weismann. Here, we address both of these propositions and outline Weismann’s theory with reference to vertebrate evolution, from amphibians to mammals. Numerous studies indicate that the inheritance of traits independent of changes in DNA sequences (i.e., epigenetics) plays an important role in development and evolution (Niklas et al. 2015). However, this phenomenology is mechanistically divorced from that of Lamarkian Binheritance of acquired characteristics^ sensu stricto, as described in Darwin’s provisional pangenesis hypothesis (Fig. 1a). Specifically, Darwin (1868) argued that (1) all cells of a multicellular organism disperse small Bgerms^ or Bgemmules^ throughout the entire organism, (2) Bgemmules^ fuse and give rise to Breproductive glands,^ and (3) the basic material for gametes are Baggregated packets of gemmulae.^Darwin (1868) also argued that the rate of gemmule production depends on environmental conditions (use/disuse of organs, etc.), i.e., Lamarckian inheritance of acquired characteristics can be explained mechanistically via gemmules. AugustWeismann rejected pangenesis, which was not supported by empirical evidence (Kutschera 2014). During the 1860s and 1870s, Weismann proposed that inheritance was due to molecular movements. He cited von Helmholtz’s (1821–1894) proclamation that Ball laws must be reduced... to laws of motion^ and thus rejected pangenesis because it was based on hypothetical Bparticles^ and not on Bmotion.^ However, the theory of inheritance proposed in the 1880s was far different from that of his earlier speculations (Weismann 1886, 1889, 1892). Therein, he made three assertions: (1) all genetic materials were contained in the nucleus, (2) inheritance was the result of the transmission of some chemical substance from one generation to another, and (3) empirical observations and his germline-soma concept (i.e., the germ plasm theory) refuted Lamarckian inheritance via use/disuse of organs etc. (Fig. 1b). Finally, Weismann (1886, 1892) proposed that sexual reproduction, and not a speculative BLamarckian mechanism,^ creates variability within evolving populations of organisms (Kutschera and Niklas 2004; Niklas and Kutschera 2014). Mayr (1982) also states that Darwin and Weismann were unaware of the actual chemical nature of Bgenetic materials.^ That some of their speculations coincide with the phenomenologies elicited by DNA methylation, histone modification, and other epigenetic phenomena is not a matter for debate. However, to propose that these phenomenologies Bsupport Darwin’s [theory of] pangenesis, and do not support Weismann’s doctrine^ seems to be an untenable example of historical revisionism comparable to claiming that Aristotle’s This is a comment to Liu and Zhi (2015) Darwin’s sub-cellular theory of inheritance: unknown or ignored? The Science of Nature