evolgen

Evolution, the Population Geneticist’s Perspective

Posted by RPM on June 15, 2006
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What is evolution? Razib started it. John Hawks joined in. I offered my opinion in the comments on GNXP. But I felt obliged to say more, here.

It seems like most of the readers in the ScienceBlogs universe don’t understand the difference between evolution and natural selection. When Razib asked them to provide the thing they would want the public to understand about evolution (in ten words or less, mind you), most of them provided explanations of natural selection. Let me say it as clearly as I possibly can, evolution is more than natural selection.

I am not a neutralist. Check out the archives of this blog for a taste of my selectionist leanings. Additionally, a large portion of my research revolves around understanding how natural selection operates on DNA sequences. That said, we cannot disregard the importance of stochastic processes. At the molecular level, stochasticity is summed up by the neutral theory (and its kissing cousin, the nearly neutral theory), which provides an excellent null hypothesis when we would like to detect selection. That’s why population geneticists spend time doing coalescent simulations — so that we’re sure that the patterns of allelic variation are due to selection and not some confounding variable such as drift or population structure.

If one wishes to understand evolution, one must understand natural selection. But to truly appreciate natural selection, one must also understand the simplest alternative, a Wright-Fisher population. That is to say, in the absence of selection, what happens? Well, allele frequencies change due to random sampling. The difference between selection and drift is that the former is deterministic whereas the latter is stochastic.

In the comments on Razib’s blog, I argued that differential inheritance of allelic variation (whether it be by stochastic or deterministic mechanisms) is the key to understanding evolution. Most people were getting caught up in unequal transmission due to fitness difference (ie, natural selection), and ignoring the stochastic effects. Whittling down my ideas into ten words left me with this:

Differential inheritance of genetic variation via stochastic and deterministic forces

That is evolution in a nutshell. Now all we need to do is make sure the public understands the definitions of the big words I used (you know, everything other than “of” and “and”).

I also like John Hawks’s explanation: “No evolution means equal offspring for everyone!” The only thing missing is that inequalities in the number of offspring can be due to random sampling or selection.

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Comments

  1. #1 coturnix
    June 15, 2006

    I would change just one word in your definition:

    “Differential inheritance of developmental variation via stochastic and deterministic forces”

    And the inheritance can be genetic or epigenetic or behavioral or whatnot….

  2. #2 razib
    June 15, 2006

    yeah, the word stochastic is pretty obscure to people. “random and predetermined.” would that work?

  3. #3 Kele
    June 15, 2006

    Maybe they also need to learn the meaning of “and” as well, considering how many people think evolution is just a random process.

  4. #4 Paul Decelles
    June 16, 2006

    Is selection strictly deterministic? For instance selection might involve differences in the probabilities that an individual survives to reproductive age. Would not that be a stochastic process? Just not one with equal probabilities for all outcomes.

  5. #5 RPM
    June 16, 2006

    In a finite population, selection may appear stochastic, but that’s because there are other things going on. Selection itself is deterministic — the most fit allele will always increase in frequency in an infite population (one devoid of all stochastic effects).

  6. #6 Peter Nielsen
    August 9, 2006

    Human mitochondrial DNA (mtDNA)/Y-chromosome phylogeography has corroborated paleo-archeological evidence that homo sapiens originated in Africa. This thus confirmed “Out of Africa” thesis corroborates my thesis at http://www.nodrift.com/vol_5/5.1.pdf and, more importantly, the corroboration is mutual.

    The correlations of my ebook’s paper 5.1 Figs 1 & 2 lead to explanations of the “Out of Africa” hypothesis, how and why African descendents of homo erectus were more successful than Asian descendents and so on, with an important corollary:

    Sexual selection may have been more important than natural selection in evolution of homo sapiens, in contrast to evolution of homo erectus, where natural selection may have been more important than sexual selection.

    The correlations: Earth’s Impact Hemisphere (IH), antipodal Africa (AA), & intermediate region (IR) correlate with the New World/Oceania, Original World, & Old World, respectively, and the distribution of so-called Yellow, Black, & White coarse race categories respectively, before an ~500 year period of world colonisation which has been undoing these probably causal associations.