Renata Contriciani flag Denunciar. Perhaps this is, in part, the fault of the evolutionists themselves for fighting so much over rather trivial differences of opinion instead of re-emphasizing the basic contents and achievements of Darwinism. Relationship between cancer of stomach and the ABO groups. Antonovics, J.
|Published (Last):||16 October 2008|
|PDF File Size:||4.53 Mb|
|ePub File Size:||14.97 Mb|
|Price:||Free* [*Free Regsitration Required]|
Renata Contriciani flag Denunciar. There are a number of reasons why I did not adopt this interpretation. First, there are pronounced ecological shifts within many widespread populous species but without any pronounced phenotypic effect on the ecologically shifted populations. Secondly, the majority of peripheral isolates, although occurring in quite novel environments, show no evidence of any major evolutionary departure, and third, some of the most drastic departures in Northern Melanesian birds such as Phylloscopus amoenus Kulambangra , Dicaeum tristrami San Cristobal , and Dicrurus megarhynchus New Ireland occur on islands that neither in the physical nor the biotic environment differ more drastically from other neighboring islands, than they from each other.
There is no indication that any selection pressure per se could account for the innovations. Eldredge and Eldredge and Gould have made my theory the basis of their theory of punctuated equilibria. What was particularly new in their theory was the emphasis on the stasis of most species after they had passed through the early speciational stage. When some of the excesses of punctuationism are removed, the theory of punctuated equilibria, or, as I prefer to call it, of speciational evolution, fits the basic Darwinian principles exceedingly well Mayr fl.
It shows that evolution is always populational, that is, gradual, and that, even though stochastic processes chance are invariably accompanying the speciational process, nevertheless natural selection is involved continuously, that is, in every single generation. The model of speciational evolution also shows why this process is so unpredictable, and why it allows such a smooth transition from intrapopulational phenomena gene frequencies to macroevolutionary innovations and trends.
Having worked with the often dramatic but always strictly gradual changes in geographic speciation, I have always been an inflexible foe of 20 Ernst Mayr saltationism.
This is one of the reasons why I was so opposed to Goldschmidt's hopeful monster theories. It was also the guiding principle in my paper on evolutionary novelties Mayr I showed that the Darwin-Dohrn principle of change of function was the explanation of many seemingly inexplicable macroevolutionary saltations.
Whenever one encounters in evolution the sudden appearance of a seemingly new structure, one must always ask oneself whether it is not something that had existed all along but had simply acquired a new function. I had written the paper on evolutionary novelties for the Chicago Darwin celebration.
The organizing committee had asked me to lecture on speciation but I was so sick and tired of that subject that I chose a theme that would not have anything to do with speciation. Little did I suspect that 25 years later the change of function principle would make a major contribution to speciation research.
If the new theory is correct that behavioral isolating mechanisms can originate by sexual selection, and only secondarily function in species recognition, then this is a classical case of change of function Mayr For most geneticists, particularly the mathematical population geneticists, it was the gene. Wright's views will be discussed presently. Their definition of evolution as a change in gene frequencies resulted in a preoccupation with the isolated gene, and an almost exclusive preoccupation with additive inheritance even overdominance is an allelic interaction.
I objected to this one-sidedness in a number of preliminary papers , but these failed to evoke any response. The Darwin Centennial in provided me with an opportunity to spell out my views in far greater detail. I decided that it might be interesting if I, a non-geneticist, would spell out what to an outsider would seem to be some of the deficiencies of current evolutionary genetics.
Since they were subsequently frequently misrepresented, I would like to quote some of my comments here verbatim. I said that there was an early population genetics that was largely mathematical 'indicated by the names Fisher, Wright, and Haldane' and a newer evolutionary genetics 'indicated by such names as Sumner, Chetverikov, Timofeeff-Ressovsky, and Dobzhansky' with its roots in population systematics. The emphasis in early population genetics was on the frequency of genes and on the control of this frequency by mutation, selection, and random events.
Each Controversies in retrospect 21 gene was essentially treated as an independent unit favored or discriminated against by various causal factors.
In order to permit mathematical treatment, numerous simplifying assumptions had to be made, such as that of an absolute selective value of a given gene. The great contribution of this period was that it restored the prestige of natural selection. Evolutionary change was essentially presented as an input or output of genes, as the adding of certain beans into a beanbag and the withdrawing of others.
This period of 'beanbag genetics' was a necessary step in the development of our thinking, yet its shortcomings became obvious as the result of the experimental population geneticists, the animal and plant breeders, and the population systematists, which ushered in a [new] era of evolutionary genetics. It is easy to see in these words the influence which the thinking of the holistic geneticists Dobzhansky, Lerner, Wallace, etc. Sewall Wright, who had been in the audience, congratulated me after my lecture.
However, when he saw the printed version, he discovered that I had bracketed him with Fisher and Haldane as a beanbag geneticist. I do not know how many papers he has published since that time, devoted to a rejection of my classification and to a restatement of his belief in the importance of epistatic inheritance. Of course he was right and I was wrong. Wright indeed had emphasized the importance of epistatic interactions all along.
In he had pointed out that 'the assignment of selection coefficients to individual genes does not give as realistic a representation of natural selection as is desirable. It is the organism as a whole that is more or less adaptive in relation to prevailing conditions, not single genes' a, p. Yet, because like Fisher he was unable to calculate the contribution of these epistatic interactions, when it came to the equations and the illustrations of his papers, they were largely beanbag genetics.
In his well known paper on isolation by distance, Wright , so far as I can see, deals only with additive inheritance, and all of the 70 or more formulae published in this paper are based on the assumption of pure additive inheritance. In the winter I spent 3 weeks with my friend J. Haldane in India, and we discussed at length the question to what extent population genetics was still beanbag genetics.
As a result, Haldane published in a paper entitled 'A defense of beanbag genetics. I had nowhere denied indeed I even had stated this specifically that as a first approach the evolutionary contributions of additive genes would have to be studied. Hence, Haldane's demonstration of the importance of some additive gene analysis required no defense in my.
Biologia Evolutiva - Douglas J Futuyma