The blog companion to The Modest Proposal

OK, a little background is in order for this post to make sense.  The Modern Synthesis in evolutionary biology refers to the mathematical theory that reconciled Mendelian genetics (think green and yellow peas from your high school biology class) and biometry (biometricians tended to study continuous traits like height).  The three main players were Ronald Fisher, Sewall Wright and J.B.S. Haldane.  There were also several others, such Theodosius Dobzhansky, Ernst Mayr and G.G. Simpson that brought speciation genetics, systematics and paleontology, respectively, into the fold.  The so-called Extended Evolutionary Synthesis is an on-going attempt to update evolutionary in light of ‘new’ findings.  If you haven’t guessed by now, I’m skeptical of this particular project, but more on that in a moment.  Recently, both Science and Nature have reported on a small conference in Altenberg, Vienna that addressed some of these ‘new’ ideas. 

I have a lot of beef with the ideas presented at the conference and elsewhere, but let me briefly focus on a couple areas:

1) Claim: [Insert your favorite topic in evolutionary biology here] was left out of the Modern Synthesis.  

This comes up again and again, and the forcefulness with which is asserted is generally in inverse proportion to its veracity.  The Nature article featured this particularly egregious quote from Sean Carroll, who did not attend, and was even critical of, the Altenberg conference.  He said that “The modern synthesis describes evolution within populations — it’s agnostic or silent about the cumulative effect of that process.”  That’s funny.  I guess Dobzhansky’s Genetics and the Origin of Species, which describes the genetic changes that cause new species to originate, and Simpson’s Tempo and Mode in Evolution, which attempted to reconcile population genetics with the paleontological record, were just a waste of paper then.

2) Claim: The new ‘evidence’ undermines or requires that we significantly adjust the theory.

A professor in my department, Mike Lynch, points out that many of those wanting to extend the synthesis generally not specifically cite what they think needs revising, so it’s hard to tell what exactly they’re talking about.  I agree.  In addition, the evidence they claim should be revolutionizing our view of evolution is extraordinarily weak - from mutant flies with weird phenotypes never observed in the wild to a disabled goat that walks on two legs, it’s completely unclear what these have to do with evolution in general.

3) Claim: Something deeply important about evolution, but which only involves human (or maybe vertebrates) is not explained by the Modern Synthesis.

Basic evolutionary theory is useful and elegant because of it’s generality.  The extenders generally care most about actually rather weird topics like the origin of human and vertebrate novelty.  They seem to forget that most life on earth does not possess a large brain or bony limbs.  Sure, maybe we need some vertebrate-specific theory to explain the origin of opposable thumbs, but this will surely be a specific case of the general rules laid out in the Modern Synthesis.  The fact is that most of the evolution focused on by these guys is not general and ignores the vast majority of biology.

I could rant more, but this will do for now.

I’m a couple days late posting because my computer crashed this week.  I’m actually up in Indianapolis right now to take it to the Apple Store for repair.  That’s really neither here nor there though.

I had a good, but brief conversation with History and Philosophy of Science PhD student Matt Dunn last night.  He is doing his dissertation on the Hist+Phil of speciation (aka the origin of species in Darwin’s parlance).  I am also studying speciation for my PhD in biology.  We were debating whether there were any rules or, at least, well supported general theories of speciation. We agreed to some extent, but I think Matt is more optimistic than me.

I would say there are two very well supported patterns, both of which are extensions of a single (mostly verbal) theory.  The first pattern is that most incompatibilities (genetic interaction that cause hybrids between species to be less fit) are recessive and don’t show up until the F2 generation (crosses between first generation hybrids), consistent with the Dobzhansky-Muller* model.  Haldane’s Rule, which posits that “When in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heterogametic) sex,” follows from this model.  That is because when there is a single sex chromosome (= heterogametic; in mammals, males have one X chromosome), all recessive incompatibilities are expressed in the first generation hybrids.  Haldane’s Rule is obeyed across pretty much all taxa examined thus far, and the exceptions will likely prove the rule (in my opinion at least).  There are some other, less well supported or general ‘rules’ (my advisor and I actually have a paper in review on this topic), but they are still somewhat controversial.

After that it gets problematic.  Matt argued that reinforcement (natural selection for species to avoid hybridizing) is an empirically supported pattern in speciation.  There are definitely a large suite of models showing that reinforcement can happen, as well as some interesting empirical patterns consistent with reinforcement.  However, there are essentially no home runs and it is generally difficult to rule out alternative explanations.  In the last ~15 years there have also been several elegant models about the accumulation of hybrid incompatibilities, but they have yet to receive unambiguous support, though that may soon change.

After that there are almost no testable theories, much less empirical support, of speciation, especially for situations that don’t involve low hybrid fitness, which is often the case.  That is, from first principles, evolutionary biologists cannot give more than a course explanation of why speciation rates vary over time and space, giving rise to patterns of biodiversity that observe today and in the fossil record.  In some sense, this is good for me because it means there is a lot to be done.  On the flip side, it’s kind of depressing when compared to, say, the mature state of particle physics, where they are about to subject the Standard Model to yet another rigorous and precise empirical examination.  Oh well, I guess that is why so much of the research money now is headed to life sciences where there are more unexplored frontiers.

* The Dobzhansky-Muller model provides an explanation for how hybrid incompatibilities can arise without the species in question having passed through a valley of low fitness, which should be opposed by natural selection.