G. Sander van Doorn
Santa Fe Institute
1399 Hyde Park Road
Santa Fe, NM 87501
sander.vandoorn@iee.unibe.ch
Dear Sander van Doorn:
I read On the Origin of Species by Natural and Sexual Selection (G. Sander van Doorn, Pim Edelaar and Franz J. Weissing SCIENCE vol. 326 no. 5960 December 18, 2009 page 1704) and am convinced by everything you say, but it seems to me you are leaving something out.
The issue is allopatric speciation, in which two populations become two different species if they are mutually isolated for long enough, and sympatric speciation, in which a population of animals becomes two different species without being isolated from each other. Allopatric speciation is an agreed upon phenomenon, but some how doubts that sympatric speciation occurs despite what appear to be likely examples.
You present a model in which an environment has a patchy distribution of resources and varying resources such that for instance a feeding strategy that works well in one area is not optimal in another area. You demonstrate that under certain such conditions, and making a few other reasonable assumptions, speciation will occur. Your model is persuasive. I think it could be made even more robust.
Consider this:
Although the allopatry enthusiasts may be quite strident in insisting on an extreme level of proof before they accept sympatric speciation, they seem to me to be quite coy about suggesting just how many generations it takes for allopatric speciation to occur. My own impression is that it takes something over a thousand generations. This is suggested by the presence of speciation among Canary Island mice, Rabbits in the Azores vs. European rabbits, dromedaries diverging from Bactrian camels and the fact that villages of mixed Bantu and pygmy populations appear to die out over time so that as one looks through Africa there are mixed villages where Bantu are recent arrivals but only straight Bantu villages scattered among straight pygmy villages in areas where the Bantu have lived longer. Alas, over the years I have misplaced the references, and besides each case requires a bit of hand waving in order to assert that speciation requires only something a little over a thousand generations. So we shall assume ten thousand generations to alllopatric speciation is typical. Although that may be on the high side, even if the number is 100,000 generations the same logic I am about to follow would hold.
Imagine a valley with 10,000 animals of some species. One day an animal from one side hops over to the other side, and while it is there a glacier descends which lasts 10,000 generations and then vanishes. When it is gone, a descendant of the first animal hops back across the valley and mates with a descendent of animals that never moved far. The match is infertile. Allopatric speciation has occurred. The chromosomes do not recognize each other. Now suppose that there never was a glacier. The first animal still hops across the valley and mates. Each chromosome then enters a pool of itself and 19,999 other chromosomes, all mating at random. By the time one of the chromosomes of a descendant of the first animal finds itself in a zygote with a chromosome of a sibling of the first animal on average more than 10,000 generations have passed. The chromosomes have no knowledge of whether there was ever a glacier or not. They simply do not recognize each other. The population by this time has died out.
So there must be some very strong restraint on drift of genes through the population. The cause could be anything. Territoriality comes to mind. But one way or other, if allopatric speciation occurs, then local genetic isolation occurs and sympatric speciation occurs. End of story.
In fact, there is excellent evidence that there is a very strong restraint on the long distance drift of genes and that is the restraint on gene pool size. As the enclosed DVD will show, in animals as well as humans, there is a rapid fall in fertility as kinship declines. The references are on the disc. It takes ten minutes to run.
So if you add this effect to your already excellent model, it would make the case for sympatric speciation very strong indeed.
In support of such a model I am also enclosing a black CD (it runs on a Windows XP platform with at least two gigs of ram and at least dual processors to avoid heat overload) which contains some relevant material. The program “Linton 2” is the one mentioned on the DVD. If you look in the file “Brisbane poster” you will find a large chart of a number of runs of populations of different sizes and at the end a list of the values of the parameters I entered.
I hope you will take an interest in this. As the disc should make clear, the relationship between kinship and fertility is now well established and enormously important in the present world. But it is stubbornly ignored. Remember those allopatriots.
There is more to be read at nobabies.net, where I shall also post this letter. If I can be of any further assistance, please let me know.
Sincerely,
M. Linton Herbert MD
Nobabies.net SilentNursery.com
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