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Home , Ernst Mayr

A Conversatonwith... Ernst Mayr

NeilA. Campbell

Ernst Mayr is one of the there, the American Museum of in greatestinfluences on evolu- New York needed an ornithologist on their expedi- tionarybiology since Darwin. tion, which was cruising in the seas near New Mayr was one of the archi- Guinea, and so I joined them. I spent the next nine ifA ; ^Jx -< tectsof the evolutionarysyn- months on a schooner in the . It was thesis of the 1930s and 40s, 2/2 years before I finally came back to Berlin. Downloaded from http://online.ucpress.edu/abt/article-pdf/54/7/412/45847/4449530.pdf by guest on 24 September 2021 whichunified by inte- Later I was invited by the American Museum of 4 ~ ^ grating Darwin's theory of Natural History to come to New York for a year, but with new my temporary visiting job became a permanent job discoveriesin ,pale- when the museum bought the Rothschild collec- ontology and . tion and I stayed with the American Museum from 'C ~:. :.f ~ Mayr basedhis views on ev- 1931 to 1953. Then I became a professor at the olution on relation- Museum of ComparativeZoology at Harvard. Ernst mainly Mayr ships of bird speciesthat he studied on Pacific islands. Now 89 years old, Mayr, NC: So you, like Darwin, were a naturalist on a professoremeritus at Harvard,is still going strong and major expedition in your early 20s. Tell us a little generatingexciting new ideas.His latestbook, One Long more about your joumey and how that early field Argument (HarvardUniversity Press, 1991), analyzes work influenced your thinking about . Darwin'stheories. We interviewedProfessor Mayr at his Mayr:My task in , given to me by Lord summercottage in New Hampshire. Rothschild, was to find the home of some rare of paradise that had been collected by the plume NC: Dr. Mayr, how did you become a naturalist? hunters for hat decorations, but had not since been Mayr: I was a naturalist ever since I could walk. My encountered. Each mountain range in New Guinea parents were very much interested in nature and took has its endemic of birds; the mountains are me and my two brothers out to watch birds, to collect like islands in the sky, as they have sometimes been fossils, to find spring flowers and everything else. So, called. Geographic takes place on these I ardently followed all of these things, but particularly mountain tops just as it takes place on islands in the birds. Since I came from a medical -there were ocean. four generations of medical doctors preceding me-I After New Guinea I came to the Solomon Islands, was supposed to be the medical doctor of my gener- where we went on our schooner from island to ation. So I went to medical school, but I also became island. There is no place in the world in which a volunteer at the Berlin Natural History Museum geographic speciation is as well demonstrated as in and that led to my giving up my medical studies. the changes from island to island in the Solomon After I had my Ph.D., which I got at the age of 21, I Islands. And that, more than almost anything else, was introduced to Lord Rothschild in England, who was the basis of my 1942 book, Systematicsand the sent me on an expedition to New Guinea. While I was Origin of Species,which was one of the books that contributedto the evolutionary synthesis of the 1930s and 40s. It is indeed true, just as Wallace had found Thisinterview is one of eight that will appear in TheAmerican in the Indonesian islands, and Darwin in the Galapa- Biology Teacher through May 1993. All are excerpted from gos, that islands are the best place in which to conversations between eminent biologistsand Neil A. Camp- demonstrate speciation. One of the things that I bell, author of the textbook Biology(Benjamin/Cummings Pub- lishingCo., Redwood City,CA). followed up later in life was to see if geographic The interviewsintroduce each unit of the third edition of separation also caused speciation on continents. In- Biology.Campbell taught general biology at CornellUniversity, deed it does. Wherever there are barriers, due to Pomona College and San BernardinoValley College for 21 years. He is now at the Uniersity of California, Rierside. water, mountains or vegetational changes, speciation can occur.

412 THEAMERICAN BIOLOGY TEACHER, VOLUME 54, NO. 7, OCTOBER1992 NC: Can you provide some historical perspective Darwin really begin to influence your view of the about the evolutionary synthesis and your role in its world? development? Mayr: Well, I wasn't nearly as much aware at that Mayr: When I was a student in Germany, I was a time that it was a Darwinian influence. I just gradu- Lamarckian,which shocks some people. But at that ally realized that natural selection can do far more time it made more sense than the view of the Men- than I thought when I was younger. I didn't read delians that all new species originate from macromu- Darwin's Originof Speciesuntil after I had published tations and that a new species is formed at once by my Systematicsand the Originof the Species.But then, one individual becoming the first representative of particularlyin the 1960s, I became very much aware the new species. The gradual speciation that I saw of the really great importance of Darwin. fitted in far better with . In the 1920s, there was still total disagreement NC: And your latest book is about Darwin's ideas. among as to what was the truth about Mayr:The reason I wrote this book is that most of the evolution and what were the mechanisms of evolu- books on Darwin speak about as if it was tion. The theory of natural selection was clearly a a single, monolithic theory. In reality, Darwin had a

minority viewpoint. Then, rather rapidly, in the great many theories. What I've tried to do is to Downloaded from http://online.ucpress.edu/abt/article-pdf/54/7/412/45847/4449530.pdf by guest on 24 September 2021 1930s and 40s, all the difficultiesseemed to evaporate separate these major theories and discuss them indi- and a modern picture of evolution originated. vidually-where Darwin got his ideas, how valid The three majorcontributions of the synthesis were they were, when they were accepted by other people, the following. First, it refuted all the opposing theo- and so forth. I've found in the literaturethat there are ries, such as Lamarckism, that believed there was seven or eight different meanings of the word Dar- some intrinsic force in organisms that would lead to winism for different people. In Darwin's own time, improvement or evolutionary change and a more for instance, Darwinism meant evolution without perfect . The second contribution was to supernaturalcausation-nothing more, nothing less. supplement the evolutionary concepts of the geneti- Today, Darwinism means the theory of naturalselec- cists of that period, who concentrated entirely on tion. But natural selection was almost totally ignored adaptive changes within a population. You won't in Darwin's time. find anything in their writings about the origin of evolutionary diversity. Adaptation and the origin of diversity are the two major components of evolution. NC: Speaking of Darwin's time, if you could go back My contributionto the evolutionary synthesis was to to that time and actually visit with Darwin, what introduce the study of diversity, the explanation of would you ask him? species, of how they originate, and how one gets Mayr: You will be very much surprised when you from there to the higher taxonomic categories. The hear my answer. I would ask him about his relationto third major contribution was that there were many religion, to a belief in a personal God. Did his loss of disparate disciplines at that time and people in dif- belief precede or follow his development of the ferent fields were hardly on speaking terms with each concept of natural selection. What went on in his other, like paleontologists and geneticists; and the mind, particularlyin relation to general things like botanists were way outside. The evolutionarysynthe- belief in religion, is something that he always care- sis brought them together, and that's why the word fully concealed in his writings, particularlysince his synthesis is so often used for this unificationof biology wife Emma was a deeply devout person. But it is through the acceptanceof Darwinianevolution. rather obvious from his handwritten notes that he didn't believe in a personal God. Furthermore,to me it seems obvious that he lost his belief in God at least NC: Did you and the other architects of the Evolu- a year, if not two, before he developed his theory of tionary Synthesis actually collaborate? natural selection. So the claim that biology and a Mayr:Curiously enough, very little. Dobzhansky and belief in naturalselection is dangerous because it may I saw each other a couple of times before I wrote my make you lose your faith in God, is not substantiated. book and I showed him my island birds. But other- That's a very important thing to know. wise we had very little contact. Simpson did his thing entirely by himself, and so did Stebbins in botany. NC: What could you tell Darwin that would help The major evolutionary theorists never had a joint him with his ideas about evolution? symposium until after the synthesis was completed Mayr: Well, I would just convey to him what we and they wrote their books independently. know about genetic variationin populations, because that's the area where he was most puzzled and where NC: Dr. Mayr, you mentioned the Darwinian stamp he was most anxious to learn more and never suc- on the modern evolutionary synthesis. When did ceeded.

A CONVERSATIONWITH... 413 NC: Many of your books and articles highlight the would evolve, because it has a bigger reservoir of importance of variation among individuals and con- genetic differences. The naturalists said, we see just trast what you call typological thinking with popu- the opposite. We see that species with very large lation thinking. What is the issue here, and why is it populations don't do anything in evolution. They so important to evolutionary theory? may stay the same for 5, 10 or 25 million years. The Mayr:Well, typological thinking, which is also some- most rapid evolutionary changes take place in small, times called , has a very long history. It isolated populations. The disagreement was strictly goes back to the ideas of Plato, who spoke of the due to the fact that the two groups of people accepted underlying eidos, the unchanging, ideal forms that different targets of natural selection. underlie all the variable phenomena of this world. The variations observed are simply incomplete and imperfect manifestations or reflections of the eidos. NC: How do you think new species most commonly Population thinking is exactly the opposite. It says arise? that there is no constant value to any variable popu- Mayr:We might as well start with a few words about lation. Every individual is unique and is different what a species is. A population which does not from all other individuals. Even in the human spe- interbreedwith another population, even though the cies, with now 5 billion individuals, every single one two occur at the same time and the same place, is a Downloaded from http://online.ucpress.edu/abt/article-pdf/54/7/412/45847/4449530.pdf by guest on 24 September 2021 of them is uniquely different. In the human body and differentspecies from the other population. Now, the in all animal bodies, most likely every cell is some- question is how two populations acquire the charac- how or other individually different from every other teristicthat they don't fuse with each other; that they cell. This emphasis on the variability of popula- are, as we say, reproductively isolated. That is the tions-on the uniqueness of the individual-is char- problem of speciation. acteristicof the so-called population thinking. Up to the 1930s and '40s, there was a widespread Darwin hadn't completed his conversion to popu- view that much of speciation is due to a group of lation thinking, though he had it essentially. You can individuals acquiring a new ecological niche at the never accept evolution by natural selection unless same place and then becoming a different species. you have adopted population thinking. For a typol- Darwin himself believed that this happens all the ogist, natural selection is ineffective, because the time. Analyzing the situation, I came to the conclu- variation does not affect the underlying ideal. sion that this must be very rare, and all the cases quoted in the literature could be much better ex- plained as examples of geographical speciation, or as NC: You view physiology as being largely typolog- it is sometimes technicallycalled, allopatricspeciation. ical in its traditional approach. This must have There are two ways in which geographic speciation important implications for medicine. can take place. Either there is a continuous area Mayr:It certainly does. I rememberthat I once talked somewhere in the range of the species in which a new about population thinking to an audience in which barrierarises-for example, a new mountain range or there were several doctors, and one of the doctors got an arm of the ocean or a new vegetational belt that up and said, "I can't accept this! Unless I treat every prevents a meeting of the individuals on either side of patient as if he were 'normal' just like all other this new barrier. That is the classical geographic patients, I wouldn't know what to do." This is one of speciation that has always been described in the the big difficulties in medicine. For instance, no two literature.But in 1954 I published a paper, which I've people react necessarily exactly the same way to always considered to be the most important paper I particular drugs. So this variability of the human ever published in my life, in which I showed that a far species is something that a modern doctor should be more important process of speciation is when some very much aware of. founders, a few individuals, establish a new founder colony beyond the existing species border. This new NC: Another point your books make is that it is the founder population rapidly changes genetically and whole organism-the whole phenotype-that is the acquires the reproductive characteristics that are object of natural selection. needed for becoming a different species. Then it can Mayr: This is absolutely so. One of the greatest exist as a separate species even if comes again in weaknesses of the mathematicalgeneticists was that contact with the mother species. they acted as if the was the target of selection. In these founder populations, more important ge- The gene is not the target of selection. A given gene netic changes can take place than when you just can be highly favorablein one genotype and lethal in separate a species into two large populations. In another context. Those who believed that the gene is these rather large parts of the species, even when the target of selection said that the larger a popula- temporarilyseparated, not very much happens. The tion-the more individuals a species has-the fasterit really important evolutionary changes probably

414 THEAMERICAN BIOLOGY TEACHER, VOLUME 54, NO. 7, OCTOBER1992 happened in the populations that came out of of organisms since the origin of life. How many of founder populations. And that is why the paleontol- these billion species have become humans? One. A ogists find so little evidence for the gradual origin of chance of one in a billion is almost like a miracle. And new species. They find a lineage that changes some- even that one human species might never have what, but not very drastically, and then suddenly a happened. We might have had several billion species new species originates somewhere else, next to it. on earth without even one of them acquiring the Eldredge and Gould based their theory of punctuated characteristics of mankind. The presumption that equilibriaon my 1954 paper. The major point which wherever there is life and evolution, then there must they added to my analysis is that once a species has eventually be intelligence is teleological thinking. become widespread and successful, it no longer I argue with the people who want to receive radio changes very much; it enters a stage of stasis. It may signals from intelligent life from all over the universe. continue in this unchanging condition for many mil- I said that the chance of our ever getting such signals lions of years until finally becoming extinct. is so small that I would consider it indistinguishable from zero. Let's say we had a billion species on earth. NC: The theory of also Only one developed the intelligence of mankind. maintains that new species usually arise relatively And then we have had at least 15 civilizations on Downloaded from http://online.ucpress.edu/abt/article-pdf/54/7/412/45847/4449530.pdf by guest on 24 September 2021 rapidly. Does this contest the traditional Darwinian earth, but only one of them produced the electronic view of gradual evolution? revolution that can send radio signals into space. Mayr: A mistake people make is thinking that if Furthermore,how many planets are there that can something evolves very rapidly, it is no longer Dar- produce life? The physical constraints are incredible. winian gradual evolution. But as long as the evolu- The fact that one of the nine planets in the solar tion occurs at the populational level, and not at the system produced conditions suitable for life doesn't level of individuals, then it is gradual evolution, mean that of the next thousand planets, even one will occurring over many generations. Some paleontolo- have the conditions suitable for life. gists call the origin of a species relatively sudden if it I've made up a little story to illustrate this point. takes place during one percent of the total life span of Imagine when the earth originated there was an the species. But that one percent is 50,000 years or intelligent civilization somewhere in the universe, 100,000years in a species living 5 or 10 million years. and they said, "Well, let's send signals to this planet, Hardly anyone else would call that sudden. it looks very promising." So for the 3.8 billion years that the Earthhad life they sent signals to the Earth and no response ever came. in the NC: Can you speculate about how your ideas on Finally year 900 they said, "We'll send signals for geographic speciation apply to the origin of humans? another thousand years, and if we don't have a then Mayr:If you look at the fossil record of the hominids, response by we'll give up." Along came the year 1900and you find that every new type did exactly what the no signal had been received. So theory of speciational evolution postulates. They they said, "No, there's obviously no intelligent life on earth," and turned up suddenly and are not a direct continuation they quit just half a century before we of the previous lineage. There's nothing intermediate developed the capability to re- spond. If you all these between Australopithecusafricanus and Homo habilis. multiply high improbabilities, you come to a as I There's nothing really in between Homohabilis and figure which, said, is indistinguish- able from zero. Homoerectus. My interpretation,which the anthropol- ogists are beginning to accept more and more, is that hominids at any time were geographically variable NC: You've also written that and had isolated groups of populations. Invariably, we humans have ex- one of these was the next step in human evolution. traordinary responsibility because of our unique- ness as a species. Mayr: Yes, humans are basically responsible for all NC: What's our current evolutionary status? the bad things that at the present time happen to our Mayr: All populations of the human species are planet, and we are the only ones who can see all these heavily exchanging with each other and there things and do somethingabout them. If we would stop is no isolated population that could become a differ- the human population explosion, we would have al- ent species. Any very widespread species is usually ready won two-thirdsof the battle. That we live here evolutionarily inert, more or less. just as exploitersof this planet is an ethic that does not appeal to me. Having become the dominant species on NC: You once wrote, "It's a miracle that humankind our planet we have the responsibilityto preserve the ever happened." well-beingof this planet. I feel that it should be a partof Mayr: Well, that was broadly speaking. On earth, our ethical system that we should preserve and main- there have probably been more than a billion species tain and protect this planet that gave origin to us.

A CONVERSATIONWITH... 415