At this point it might be well to insert a fact that has generally been overlooked by the historians of biology. The pre-evolutionary concept of species is generally given as a universally accepted view that species were constant and true breeding forms. Actually, the idea that species were completely stable and unalterable units had dominated biological thought for only about a hundred years when Darwin attacked and shattered it. All during classical and medieval times, species were looked upon as something specious. The species of an object were only its appearances and, proverbially, appearances were deceitful. Supposedly, species were only temporary forms and they could change into each other whenever the occasion demanded. Wheat could “degenerate” into barley, and barley into oats. Promiscuous and unsystematic hybridization supposedly could also produce new species. Both animals and plants had been described as changing their species whenever they were transported to new countries. But this widely accepted concept that species were only ephemeral and mutable units did not lead to a belief in evolution.
Before a belief in an orderly and systematic evolution could become respectable, the relative stability of species would have to be established. And, in the eighteenth century, as the result of careful and accurate research in the field of systematics, this view of species I did supersede the older one. But this careful research also showed that the stability of species was not absolute. There was evidence that some species had become altered, even if only a little bit. It was the secular accumulations of this residual instability in otherwise stabIe species that led to the theory of evolution.
From The Evolution of Biology (M J Sirks and Conway Zirkle, New York, Ronald Press, 1964: 305)
This is basically what I argue in my Species book. I am getting used to finding that the older and unappreciated historians did the same thing I did much later. They are generally very good historians.
Incidentally, I have been chided (chid?) by a recent reviewer for my use of Eric Nordenskiöld’s History of Biology, which was published in 1929. Why, I am unable to tell. Up until the period with which he is contemporary, he is a very good scholar, and his only sin with respect to the modern period is that he did not end up on the “right” side of history and gave credence to neo-Lamarckism. His scholarship, however, is impeccable, and he is a very useful source of citations that have been ignored or forgotten by the enlightened modern contextual historians who take Ernst Mayr seriously as a historian.
In general I find that the late nineteenth and early twentieth century historians of biology are more general, less Whiggish, and overall less likely to engage in simplistic dichotomies of internalistic issues. I was also chid (chided?) by that reviewer for doing an internalist history, even though I had given my apologia for doing so in the preface, and the reviewer gave no reason for thinking I should not have done one. Some fashions are ruling illusions, I guess. I even said that I hoped someone would do an externalist social history of “species”, but I guess that passage escaped the filter of the reviewer.
So I do not apologise for failing to follow fashions of either kind.