# What Are The Chances? Mathematician Solves Evolutionary Mystery: Science Daily

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For the last two years, Iosif Pinelis, a professor of mathematical sciences at Michigan Technological University, has been working on a mathematical solution to a challenging biological puzzle first posed in the journal "Statistical Science"*: Why is the typical evolutionary tree so lopsided?

In other words, why do some descendants of a parent species evolve hundreds of different species, while others produce so few they seem to be practicing family planning?

http://www.sciencedaily.com/releases/2003/09/030929055601.htm

## Answers and Replies

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So the speciation rule seems to be the same one that applies to websites "Them as has, gits".

Now what they need to explain is th Yucca plant effect, pointed out by Stephen Gould, lineage trees of genera tend to be bushy near the bottom (many short lived species early in time) with a spike (one or a few species surviving to later times).

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Hummm. Well, I am certainly in no position to argue with a professional mathematician but, yeah, it seem likely to me that if you already have more species in group A than group B, then as time moves along, you would see more future species arising out of the A group lineage than the B - all things being otherwise equal. I would also be surprised that professional evolution theorists haven’t realized this obvious probability for some time.

And, all things are not equal. What I am particularly curious about is the thinking on the “living fossil” reason for the “lopsidedness”. I wouldn’t have thought (and I am not now convinced) that the answer for the question of unequal speciation events lies predominantly there. I would explain it as simply (maybe too simply?) a result of unequal selection pressures on species for significant, that is species-creating level, changes in the world’s biota through time.

Each species is experiencing its own level of selection to change. Things like geological isolating mechanisms (continental movements, island development, mountain building, lake isolation, etc) and climate changes, for instance, would exert natural selection pressures on populations of species to shift genotypes (natural selection). Genotype changes might also come about in isolated populations through the Founder’s Effect and genetic drift. These mechanisms are, of course, the standards in most current models of how evolution occurs at both the within-species level (microevolution) and at the species-creating levels (macroevolution). Lay this template upon the simple mathematical one (above) and you wouldn’t expect to see the “bush of life” to have equal speciation rates, would you? After all, so many contingencies, in unique configurations, are at always in play for any species: all of the above plus the added variables of population size and existing genetic diversity, and others.

Also, I didn’t realize that the existence of comtemporary species with long histories (“living fossils”) was a big intellectual concern for evolution theorists either. I thought it was explained as a simple consequence of a lineage evolving to a “highly fit” genotype/phenotype long ago in a relatively unchanging environment.