Now this book, published in 1942, became one of the foundation publications of the evolutional synthesis because I, even more than Dobzhansky, brought in the whole subject of species and speciation and their relation to evolution. This book is still considered a classic and still being published. At first it was slow but every new printing – I always printed a thousand copies – every new printing sold out more quickly than the preceding one because Columbia University Press never did it… never advertised it, but the book advertised itself, so to speak. Now let me say a few things about the contents of the book. I was, after all, a taxonomist who wrote that book, and… when I look back at it now, many people consider it a book on evolution and indeed it was also a book of evolution, but it was at the same time very much a book on the principles and methods of systematics. And, in fact, it was the first pronouncement… the first real… certainly in the English language… presentation of the so-called new systematics, that’s the species level systematics. And I introduced a lot of new concepts which were certainly new to the American audience, even though some of them were things that I had learned from [Erwin] Stresemann and from Rensch and other European authors. And as a matter of fact, there was simultaneously a similar development in the systematics in… in Russia, and there are some historians working on it now. But at any rate, as far as America was concerned, this was mostly to everybody something very new. And the other half, of course, was that I used this new knowledge of species and speciation to show how this contributes to an understanding of one of the two great areas of evolutionary biology. Evolutionary biology has two great areas: the one is the origin of adaptation which is explained by the changes within a population, within a gene pool owing to natural selection, and the other great area is the explanation of the origin of… organic diversity, of biodiversity and that includes the whole thing of species, speciation and a connection between that and macro-evolution, that means the evolution of higher categories, of higher types, of evolutionary novelties of… all the things that go over long periods of time and that, for instance, also interest the palaeontologists. And in the part in which I tried to prove that geographic variation leads to speciation, I employed among other things, what I thought was a new technique and in a way, in that connection, it was a new technique. And that is… you cannot… speciation takes time, thousands of millions of years… so you cannot follow it by experiment or anything like this, you have to infer it by an indirect method, and the method that I used was exactly the same method the cytologists had used in the 19th century to explain cell division. They just took lots and lots of pictures of dividing cells and finally put them in sequence so that they had a complete picture now from the very beginning of a dividing cell to the very end of a dividing cell. And so I did… by showing cases where populations that had been isolated were just partly and very slightly different from each other to cases where they were more different with each other, ever more, until finally cases where they were so different that you could say they’re already new species, or they’re very near being new species. This same process as putting together, different pictures of a dividing cell, I put together, so to speak, different maps of dividing an isolated and diverging populations. That book had a… I think I can rightly say… a… a very considerable impact because this area of evolutional biology had been totally ignored and neglected by the geneticists, and you go to the writings of the great population geneticists: Fisher, Haldane, Sewall Wright. Sewall Wright, incidentally, in that lecture in Columbus, Ohio, talked about evolutionary change within a lineage, but not about how species multiply, which was my problem.