Circulating nucleic acids and Darwin's gemmules

In a recent review article “Circulating nucleic acids and evolution,” Anker and Stroun suggest that circulating nucleic acids, like Darwin's gemmules, play a role in the mechanism of evolution [1]. I greatly appreciate this viewpoint not only because it is consistent with my idea but also because it is of great interest and importance in genetics and evolution.

To my knowledge, as early as 1960s, Stroun and colleagues conducted a series of experiments on plant graft hybridization and animal vegetative hybridization (heritable changes induced by grafting and blood transfusion), which are two cases in support of Darwin's theory of heredity – pangenesis. Based on their excellent researches on bacteria, plants, animal cells and organs, blood plasma and serum, Stroun and colleagues suggested that nucleic acids are released by living cells and circulate throughout the whole organism, providing a modern version of Darwin's pangenesis, although they did not know Darwin's pangenesis at that time. It should be admitted that it is Stroun's work on circulating DNA and Lucas's work on RNA transport that greatly inspired me and led me to realize the striking similarity between Darwin's gemmules and circulating nucleic acids [2,3].

I much enjoyed reading Anker and Stroun's article, but one mistake needs to be corrected. They stated that Darwin ignored Mendelian heredity [1]. This is not the case. In his book The Variation of Animals and Plants under Domestication, Darwin described many cases of “prepotency”, which corresponds to what we now recognize as dominance inheritance or Mendelian inheritance [4]. For example, in the crossing of snap-dragons Darwin found that when the normal or irregular-flowered type is crossed reciprocally with the peloric or regular-flowered type, the former prevails in the first generation to the exclusion of the latter. The 127 hybrid plants, self-fertilized, yielded in the second generation irregular to regular plants in the ratio of 88 to 37, approaching 3:1. These cases in which the characteristics of one parent dominate was explained by Darwin to be a consequence of that parent's gemmules having some advantage in number, affinity, or vigor over those derived from the other parent. Pangenesis is a highly comprehensive theory Darwin constructed to explain a far wider range of phenomena than Mendel had considered. It not only explains graft hybridization and the inheritance of acquired characters, but also explains dominance inheritance, reversion, regeneration, xenia, telegony and many other facts.

Author's response:

Philippe Anker

We thank Dr Liu for his interest in our article on circulating nucleic acids and evolution. In fact, Yongsheng Liu was the first to bring back Darwin's pangenesis and link it to circulating nucleic acids. His remark that the notion of prepotency corresponds to what we now call dominance inheritance is perfectly correct. One more time, Darwin proves to be more modern than usually thought to be! Our sentence stating that “Darwin did not know anything about DNA and ignored Mendelian heredity” is therefore only true for the first part.