Re: Common descent before Darwin?

Bobby D. Bryant wrote:
What was the status of the idea of common descent before Darwin
published? Was the idea current among scientists, and Darwin
just provided a mechanism? If so, how widespread was it?


That species were organised into tree diagrams, or logical classifications
that could be presented as tree diagrams, was widely known. It was part of the
inheritance of logic. For example, George Bentham (nephew of the famous
Jeremy) published a logic text in 1827 with tree digrams in it using
biological examples, before he turned himself to botany (and became a famous
botanist, and a friend of Darwin's).

Karl Ernst von Baer proposed a classification of sorts based on developmental
divergence which was published in Scotland as a tree diagram by a commentator,
and it has been argued that Darwin was influenced by this.

Darwin's trees are slightly ambiguous. The logical tradition allowed only for
dichotomous trees, and while Darwin's diagram in the Origin has many branches,
if you step back a bit and look at the whle thing, you'll see that the overall
phylogeny is dichotomous.

However, I am not aware of anyone who proposed common descent as Darwin did
before him. Lamarck had a variable branching at about the phylum level but
nobody treated of speciation as the basis for common descent or "groups under
groups". A tradition known as Quinarianism held that species were arrayed in
quintuplets around the edges of a circle and had affinities with species from
other groups in "osculating" (i.e., touching or kissing) circles. Basically
there was a lot of confusion before 1859.

IMO Darwin's greatest contribution, and the one that earned acceptance of
evolution, was common descent.

--
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: evolvethought.blogspot.com
Who are you going to believe? Me, or your own eyes?

.

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