Interview with Ernst Mayr

BIES: Dr Mayr, I’d like to begin with several questions about your history and the history of ideas in evolutionary biology, then focus on some questions about specific issues in evolutionary biology and, finally, conclude with a discussion of some matters in the philosophy of science and of biology in particular. Let’s begin with the matters of history. This year is the 60 anniversary of publication of your book Systematics and the Origin of Species, one of the great classics of evolutionary biology. It was published 5 years after another classic in the field, Theodosius Dobzhansky’s Genetics and the Origin of Species. You were a colleague and friend of Dobzhansky’s, but you clearly felt that his book neglected certain important issues. What were the specific factors that led you to write Systematics and the Origin of Species? (Figure 1) EM: The reason I wrote the book was that I was asked by Columbia University and, more particularly, by Prof. [L.C.] Dunn of the zoology department at ColumbiaUniversity to give one of the Jesup lectures. This was a famous lecture series dealingwithmanyproblems, but particularlywith evolution and Dobzhansky had given a previous lecture. Now Dobzhansky hada feeling that hehadnot doneagood jobwith respect to the problem of speciation and the whole question of biodiversity and its evolution. In his 1937 book he has no chapter on speciation, andhewas verymuch interested in amoredetailed treatment of this subject. He knew from many conversations that we had had, that this was a field in which I was not only interested but was also really an expert, and so he suggested that I give a Jesup lecture in this field, with the understanding that it might lead to a book later. Now to give the full details: the 1941 Jesup lectures were given by two people. I gave two lectures on speciation and the species problem in animals and Edgar Anderson, a botanist, gave them on plants. Anderson got sick, however, andhenever submitted amanuscript. I was, therefore, asked by Prof. Dunn to expand my two lectures into a book. That book was Systematics and the Origin of Species and there I dealt with the neglected parts of Dobzhansky’s book. BIES: Your book incorporated Neodarwinian ideas about genetics but when you first entered the field of systematics biology you believed in the inheritance of acquired characteristics, at least to some extent. At what point did those ideas fade away and what caused you to abandon them? EM: It is indeed true that at the time when I started working at the American Museum of Natural History in 1931, that I was still a Lamarckian, believing in the inheritance of acquired characteristics and therewere good reasons for that which are usually forgotten by the historians of genetics. When in 1900 Mendel was rediscovered, there were three geneticists who were particularly interested in the evolutionary aspects of genetics. These threewereBateson,DeVries and Johannsen. All three of them were typologists; all three thought new species originated with major mutations, ‘saltations’, and all three of them rejected natural selection. That is usually carefully concealed by the geneticists, but this was what we, the naturalists, were fighting in particular. We all knew that speciation and evolution was a gradual process and since geneticists believed it had to be by saltation, we had to find a different answer for thegradualness. Theonly answer thatwas available was Lamarckian gradual acquisition of new characteristics by use and disuse etc. So the important thing that had to happen, and this did indeed happen in the years between 1916 and 1932, was that the geneticists completely rejected the saltationist views of the early Mendelians and showed that genetic changes could happen through very small mutations and that even very small mutations in the long-run could be of great evolutionary influence. Forme, a crucial interaction was with an ornithologist at the American Museum of Natural History, namely James P. Chapin who had got a PhD at Columbia University in 1920 dealing with bird geography and ecology. He was, of course, fully familiar with the modern genetics of T.H. Morgan, who was in the same department. He and I had numerous conversations on evolution and he convinced me of the importance of the findings about the effects of small mutations etc. and of the invalidity of any belief in inheritance of acquired characteristics. Most importantly, he helpedme to see that the gradual evolution that we naturalists had insisted on could be explained by the new genetics of Fisher and the other modern geneticists and didn’t require any of the saltational interpretation of the early Mendelians. On the other hand, the geneticists during the 1920s and 1930s completely adopted natural selection which they had previously rejectedandso therewasanentirely newbasis for a reconciliation with the naturalists. Yet the geneticists, and you can look at the writings of Fisher, Haldane and Wright to see this, did not understand speciation at all, and correspondingly