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Mayr Had Proposed Many Models of Speciation

Mayr Had Proposed Many Models of Speciation

In the field of biological evolution, Ernst Mayr is a well known person. He was born in 1904 in the southern German city of Kempton, and died in 2005, lived over 100 years. During his life, he published over 700 scientific papers, and a few dozens of books and won many awards.  In his 100th birthday, Science published an article to honor him. According to his colleague Edward O. Wilson at Harvard, Meyer is not only the greatest evolutionary theorists of the 20th century, but also the greatest biologist in the century.

It is not so easy to know what contribution he did for the theory of evolution, and many of his books have 600-700 pages, it would take a few months just to browse them. It is generally agreed that he played important roles in following fields.

1. Definition of Species

What is a species? It had been perplexed issue among biologists. Mayr and Dobzhansky proposed the “biological species concept”: “Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups” (MAYR 1942, p. 120).

Individuals in same species can mate and give birth to healthy offspring that also gives rise to new healthy offspring by mating . Horses and donkeys can mate and give birth to a healthy  mule, however, the mule does not give birth to another mules, so horses and donkeys are not a same species. “Biological species concept was proposed more than a half-century ago, and  is well-accepted among biologists.  Mayr and Dobzhansky made their positive contribution to understanding evolution.

2. Founder of “Modern Synthesis” 

The modern synthesis or Neo-Darwin was established in 30-40’s of the last  century, which combines  the ideas from several specialties and tries to provide sound explanation of evolution with modern biological knowledge. Ernst Mayr was one of major advocates of the theory. (See: What is the Neo-Darwinism?)
3. Role of Isolation in speciation

In his book, Systematics and the Origin of Species, Mayr argued that the most significant way to cut off a population is by geographical isolation (see illustration at right). For example, a glacier may thrust down a valley, creating two separate populations, one on either side of the glacier. A rising ocean may turn a peninsula into a chain of islands, stranding the beetles on each of them. This sort of isolation doesn’t have to last forever; it needs only form a barrier long enough to let the isolated population become genetically incompatible with the rest of its species. Once the glacier melts, or the ocean drops and turns the islands back into a peninsula, the animals will be unable to interbreed. They will live side by side, but follow separate evolutionary fates.

http://evolution.berkeley.edu/evolibrary/article/history_21

His idea is if a new mutation must occur on individual, not by a group. The mutants have to mate with other individual without mutation, the new mutant would be diluted out or not fixed without geographical isolation, would not have made new mutant into population, therefore a new species could not be generated.

A simple question is even a new mutants can not mate with others in the opposite side of geographical barriers; it still can mate with others located in the same side, and such mating would also the new mutant will be diluted out

He proposed GI theory in the 1930s, scientists have made ​​a lot of efforts to test the idea. It is regrettable that many new species were discovered, very, very few of them (if any) are separated by geographical barriers. Faced with these findings, he proposed a new concept, called a micro-geographical isolation. What is a micro-geographical isolation? The idea requires you imagine an invisible wall across a dinner table. Thus, even new species is found next to each other, you still can imagine a physical barrier between them.

He is considered as the 20th century Darwin, which is unfair for him and Darwin. The main idea of the Darwin’s theory  is that natural selection the main driving force for speciation, whereas Mays claimed that GI the major one, natural selection dispensable (such as in the genetic drift).

The lack of intermediate fossil has been a big confusion in the biosphere. 1972  the American paleontologist N. Eldredge and SJ Gould proposed theory called “punctuated equilibrium”. Strictly speaking, the “punctuated equilibrium” is a real theory. It just says: rather than hiding it, it is better to face it. There are few transitional fossils fossils, it should be like that (See: What is Achilles Heel of “Punctuated Equilibrium”?)
Mayr seemed loss of his interest on speciation by isolation with big river or mountain. He claimed to publish his idea of the peripatric speciation or founder effect long time ago (Somit and Peterson, 1992), which was consistent with the “punctuated equilibrium”. Actually, the theory does not hold water either.

We can proceed according to Mayr’s ideas. For example, there are 10 birds with blue eyes that are separated from a great flock due to some physical barriers. A mutation occurs in one of the birds which caused her eye become yellow. Yellow eye does not spread to other birds by infection. In order for the bird with yellow eye spread among the small population, the bird has to mate with other birds in blue eyes to give birth to fertile birds, which mean them same species. We assume that the process continue until all birds in the small population have yellow eyes (100% frequency), why and how do they become a new species? Mayr did not tell. What he said is just accepting it as a fact, do not ask why.

So-called “founder effect” is very similar to the idea of saltationism, in which a new species are generated instantly, there are neither Darwinian natural selection, nor geographical barriers, the idea was strongly opposed by him and other mainstreamers, he did not realize or want to admit it.

Beside the geographical isolation, Mayr also proposed or accepted other ways of speciation, such as sympatric speciation (speciation without isolation), instantaneous speciation (speciation without natural selection and isolation), founder effect (speciation from a very small isolates), dichopatric speciation, parapatric speciation, speciation by distance (ring species), speciation by hybridization. (What Evolution Is page p176-183)

According to him, new species can occur at any locations, ones do not need care his idea of the geographical isolation, as he told you so.            http://tinyurl.com/2owb32

Mayr had a career as an evolutionary theorist for nearly 80 years, he proposed several ideas, and kept modifying these ideas back and forth.

This is what he said in 1963:

“the proponents of the synthetic theory maintain that all evolution is due to the accumulation of small genetic changes, guided by natural selection, and that trans-specific evolution is nothing but an extrapolation and magnification of the events that take place within populations and species.” (Mayr 1963).

In 2001, he changed his tone:

Evolution, being on the whole population turnover, is ordinarily a gradual process, except certain chromosomal processes that may lead to the production of a new-species-individual in a single step. (Mayr 2001).

His natural selection has a quite different meaning from one Darwin proposed (See: What is the Darwin’s Theory? ), the idea of geographic isolation makes the Darwin’s theory not necessary, he strongly criticize the idea of “hopeful monster”, but his “founder effect” convey the same thing. He stated geographical isolation essential for speciation, but also accept speciation without it.

He even had many contradictory ideas in a same book. In one of his famous book: What Evolution Is, he wrote:

Indeed, all pre-Darwinian evolutionary schemes postulated essential straight phyletic lineages. One of Darwin’s major contribution was to have proposed the first consistent theory of branching evolution. (Page 19)

We know that the origin of new species does take place continuously and we must therefore search for the mechanism that produces such a multiplication of species. We want to find out how the millions of existing species originated. The process of the multiplication of species is something entirely different from the phyletic evolution of species in a fossil lineage. …. Darwin himself failed to solve the problem of speciation. (Page 174-175) 

In my 1942 Systematic and the Origin of Species, I showed that in these groups geographic isolation had been the exclusive mechanism of speciation and not a single case of sympatric speciation had been demonstrated. 

The exclusive occurrence of allopatric speciation in mammals and bird, however, does not refute the possibility of the sympatric speciation in other groups of organism. (Page 180)

I copy and paste some posts in website to let readers to see what comments others have on him:

“The problem with Mayr is that he said so many, often contradictory, things that he can take credit for almost anything.”

“My point is simply that Mayr was anti-saltationist but also claimed that he laid the foundation for punctuated equilibria, such that they are obviously distinct items.”

http://tinyurl.com/878fl4t

Scientists are not “saints”.  If a scientist alleges a theory correct, he/she should insist on it, if he/she considers a theory incorrect, and should have courage to admit it wrong, rather than changing own position back and forth to evade it. Even he was obviously wrong, he never admitted that; instead he kept modifying his ideas to make them fit all possibilities.

Mayr had proposed many ideas, what one is correct? Is any of them right? The mainstream has been a pseudoscience (See: Why is the Neo-Darwinian theory a pseudoscience?), Mayr definitely played important roles in making it happen.

References

MAYR, E., 1942 Systematics and the Origin of Species. ColumbiaUniversity Press, New York.

Mayr, E. (1963). Animal species and evolution. Cambridge, Belknap Press of HarvardUniversity Press

Mayr, E. (1988). Toward a new philosophy of biology : observations of an evolutionist. Cambridge, Mass., Belknap Press of HarvardUniversity Press.

Mayr, E. (2001). What evolution is. New York, Basic Books.

Meyer, A. (2005). “On the Importance of Being Ernst Mayr.” PLoS Biology 3(5): e152.

Somit, A. and S. A. Peterson (1992). The Dynamics of evolution : the punctuated equilibrium debate in the natural and social sciences. p. 21-48. Ithaca, CornellUniversity Press

“Mayr’s hypothesis of peripheral isolates and genetic revolution must of necessity be a centerpiece of the punctuated equilibria theory.”  … I believe I was the first author to develop a detailed model of the connection between speciation, evolutionary rates, and macroevolution (Mayr, 1954). Although long ignored, my new theory of the importance of peripatric speciation in macroevolution is now widely recognized. ” Mayr’s hypothesis of peripheral isolates and genetic revolution must of necessity be a centerpiece of the punctuated equilibria theory; it is the theory, for all practical purposes”

28 thoughts on “Mayr and His Theories

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  10. Thanks for the read.

    I recall reading Mayr’s “What Evolution Is,” and realizing that several of his ideas about speciation were, frankly, untestable and wholly ad hoc.

    He’s one of the reasons I compiled my theory of life. To challenge the neo-Darwinian paradigm directly.

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