Charles Darwin was not a Scientist

"The existence of free gemmules is a gratuitous assumption"

Translation : "I have no idea and I can't back that up in any way, I'm just making this up as I go along."

[page] 502

PANGENESIS

IN a paper, read March 30, 1871, before the Royal Society, and just published in the Proceedings,¹ Mr. Galton gives the results of his interesting experiments on the inter-transfusion of the blood of distinct varieties of rabbits. These experiments were undertaken to test whether there was any truth in my provisional hypothesis of Pangenesis.² 

Mr. Galton, in recapitulating "the cardinal points," says that the gemmules are supposed "to swarm in the blood." He enlarges on this head, and remarks, "Under Mr. Darwin's theory, the gemmules in each individual must, therefore, be looked upon as entozoa of his blood," &c. 

Now, in the chapter on Pangenesis in my "Variation of Animals and Plants under Domestication," I have not said one word about the blood, or about any fluid proper to any circulating system. It is, indeed, obvious that the presence of gemmules in the blood can form no necessary part of my hypothesis; for I refer in illustration of it to the lowest animals, such as the Protozoa, which do not possess blood or any vessels; and I refer to plants in which the fluid, when present in the vessels, cannot be considered as true blood. 

The fundamental laws of growth, reproduction, inheritance, &c., are so closely similar throughout the whole organic kingdom, that the means by which the gemmules (assuming for the moment their existence) are diffused through the body, would probably be the same in all beings; therefore the means can hardly be diffusion through the blood. 

Nevertheless, when I first heard of Mr. Galton's experiments, I did not sufficiently reflect on the subject, and saw not the difficulty of believing in the presence of gemmules in the blood. I have said (Variation, &c., vol. ii., p. 379) that "the gemmules in each organism must be thoroughly diffused; nor does this seem improbable, considering their minuteness, and the steady circulation of fluids throughout the body." 

But when I used these latter words and other similar ones, I presume that I was thinking of the diffusion of the gemmules through the tissues, or from cell to cell, independently of the presence of vessels,—as in the remarkable experiments by Dr. Bence Jones,³ in which chemical elements absorbed by the stomach were detected in the course of some minutes in the crystalline lens of the eye; or again as in the repeated loss of colour and its recovery after a few days by the hair, in the singular case of a neuralgic lady recorded by Mr. Paget.⁴ 

Nor can it be objected that the gemmules could not pass through tissues or cell-walls, for the contents of each pollen-grain have to pass through the coats, both of the pollen-tube and embryonic sack. I may add, with respect to the passage of fluids through membrane, that they pass from cell to cell in the absorbing hairs of the roots of living plants at a rate, as I have myself observed under the microscope, which is truly surprising.

When, therefore, Mr. Galton concludes from the fact that rabbits of one variety, with a large proportion of the blood of another variety in their veins, do not produce mongrelised offspring, that the hypothesis of Pangenesis is false, it seems to me that his conclusion is a little hasty. His words are, "I have now made experiments of trans-

¹ Francis Galton (1822-1911), traveller, statistician, scientific writer and founder of the eugenics movement. CD's half-first cousin. Galton 1871a. 

² First published in Variation vol. 2, chapter 27. 

³ Henry Bence Jones (1814-1873), physician and chemist and Darwin's personal physician for twenty years. Bence Jones 1865a and 1865b. 

⁴ James Paget (1814-1899), surgeon. Paget 1853, 1: 46, states: 

A lady who is subject to attacks of what are called nervous headaches, always finds next morning that some patches of her hair are white, as if powdered with starch. The change is effected in a night; and in a few days after, the hairs gradually regain their dark brownish colour. 

Darwin cited this case again in the second edition of Variation vol. 2, p. 374. 

[page] 503

fusion and cross circulation on a large scale in rabbits, and have arrived at definite results, negativing, in my opinion, beyond all doubt the truth of the doctrine of Pangenesis." If Mr. Galton could have proved that the reproductive elements were contained in the blood of the higher animals, and were merely separated or collected by the reproductive glands, he would have made a most important physiological discovery. As it is, I think every one will admit that his experiments are extremely curious, and that he deserves the highest credit for his ingenuity and perseverance. But it does not appear to me that Pangenesis has, as yet, received its death blow; though, from presenting so many vulnerable points, its life is always in jeopardy; and this is my excuse for having said a few words in its defence. CHARLES DARWIN

¹ Galton replied in Galton 1871b.

Ernst Mayr's 1942 book was a turning point for the species problem.[5] In it, he wrote about how different investigators approach species identification, and he characterized these different approaches as different species concepts. He also argued strongly for what came to be called a Biological Species Concept (BSC), which is that a species consists of populations of organisms that can reproduce with one another and that are reproductively isolated from other such populations.

Mayr was not the first to define "species" on the basis of reproductive compatibility, as Mayr makes clear in his book on the history of biology.[13] For example Mayr discusses how Buffon proposed this kind of definition of "species" in 1753.

Theodosius Dobzhansky was a close contemporary of Mayr and the author of a classic book about the evolutionary origins of reproductive barriers between species, which was published a few years before Mayr's.[18] Many biologists credit Dobzhansky and Mayr jointly for emphasizing the need to consider reproductive isolation when studying species and speciation.[19][20]

Mayr was persuasive in many respects and from 1942 until his death in 2005, both he and the Biological Species Concept played a central role in nearly all debates on the species problem. For many, the Biological Species Concept was a useful theoretical idea because it leads to a focus on the evolutionary origins of barriers to reproduction between species. But the BSC has been criticized for not being very useful for deciding when to identify new species. It is also true that there are many cases where members of different species will hybridize and produce fertile offspring when they are under confined conditions, such as in zoos. One fairly extreme example is that lions and tigers will hybridize in captivity, and at least some of the offspring have been reported to be fertile. Mayr's response to cases like these is that the reproductive barriers that are important for species are the ones that occur in the wild. But even so, it is also the case that there are many cases of different species that are known to hybridize and produce fertile offspring in nature.

After Mayr's 1942 book, many more species concepts were introduced. Some, such as the Phylogenetic Species Concept (PSC), were designed to be more useful than the BSC for actually deciding when a new species should be described. However, not all of the new species concepts were about identifying species, and some concepts were mostly conceptual or philosophical.