Category Archives: evolution

The Molecular Ecologist: If genes aren’t independent “beans,” speciation is easier

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Three-spined stickleback profile Threespine sticklebacks are a classic case of speciation caused by natural selection. Photo by wolfpix.

This week at The Molecular Ecologist, my friend and collaborator Chris Smith writes, with two coauthors, about a new study simulating adaptive speciation in the face of gene flow, and the effects of linkage among genes involved in the adaptive divergence:

Models of speciation that involve ongoing gene flow remain controversial because gene flow is expected to homogenize differences between populations. However, genome-level effects may facilitate speciation with gene flow. For example, selection against immigrants may have the effect of reducing realized gene flow, even at loci that are not under divergent selection (Rundle & Nosil 2005). This global reduction in gene flow and increased divergence across the genome due to divergent selection is termed ‘Genome Hitchhiking’ (Feder et al. 2012). Genome hitchhiking may be enhanced by fitness epistasis – multiple loci interacting synergistically to cause reductions in fitness that are greater than selection acting on any one locus.

It turns out that speciation is more probable in models that don’t treat genes like independently evolving beans in a beanbag, bearing out a classic criticism of simple speciation models made most prominently by Ernst Mayr. However, true linkage among the selected genes isn’t necessary, either. All in all, this is an exciting new development for those of us who think natural selection might be important in forming new species, so you should definitely go read the whole thing.◼

Evolutionary psychology: You’re doing it wrong (but you could do it better!)

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The Descent Of Man Well, it didn’t quite happen like that. Photo by Minette Layne.

Over at Scientific American, Kate Clancy sums up the scientific case against evolutionary psychology:

[Evolutionary psychology] is trying to take on an incredibly challenging task: understand what of human behavior is adaptive and why. We can better circumvent the conditions that lead to violence, war, and hatred if we know as much as we can about why we are the way we are. What motivates us, excites us, angers us, and how can evolutionary theory help us understand it all?

Because of this, there are consequences to a bad evolutionary psychology interpretation of the world. The biggest problem, to my mind, is that so often the conclusions of the bad sort of evolutionary psychology match the stereotypes and cultural expectations we already hold about the world: more feminine women are more beautiful, more masculine men more handsome; appearance is important to men while wealth is important to women; women are prone to flighty changes in political and partner preference depending on the phase of their menstrual cycles.

It may not always be evident, but biologists who get all shirty when we see the latest evo-psych study splashed across the headlines generally agree with the most basic premise of EP: that humans are evolved, biological organisms, and that our present behavior is a result of our evolutionary history. What drives us up the wall is the refusal of EP research to apply understanding developed over decades of work by evolutionary biologists—the discovery that there’s more to evolution than natural selection, that natural selection often acts on many traits simultaneously, and that there may be many ways to acheive the same level of reproductive success.

With modern genetic tools and a modern evolutionary perspective, biologists—including Kate, who studies human reproductive biology in an evolutionary context—have learned a lot about how natural selection and other evolutionary processes shaped current human diversity. Some of the best examples so far are in relation to diet (drinking milk and cultivating corn) and adaptation to low-oxygen conditions at high altitude; but there’s no reason the same methods can’t tackle other features of human nature, given sufficient quantities of the right data. Yet we rarely see EP studies based on the kind of data that could actually provide answers to the questions they ask. (And then, all too often, we see EP studies that are unmoored from basic biology altogether.)

So: The complaint that most evolutionary biologists have with EP isn’t that it’s asking the wrong questions, or asking questions it has no right to ask. It’s that EP is using the wrong tools to answer those questions. And, to the extent that we agree that those questions are important, it’s upsetting to see someone claim to have answered them using only surveys of undergraduates. We’re like plumbers expressing our exasperation with a guy who insists on intalling a new toilet using a nail file and a hot glue gun: dude, go buy a wrench!

Anyway, enough from me. Go read Kate’s post already.◼

Herd immunity, unfalsifiable hypotheses, and the search for the missing heritability

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Image created with Pulp-O-Mizer.

It’s been a busy week at the other blogs with which I’m variously affiliated. So busy that I’m going to run down what’s up at Nothing in Biology Makes Sense! and The Molecular Ecologist in a single omnibus post.

First up, Nothing in Biology Makes Sense!: My younger brother Jon (@Bonovox1984), who’s in his third fourth year of medical school, led off with a post on a new study of “herd immunity”—the effect whereby people who haven’t been vaccinated benefit from reduced risk of disease if they’re living around lots of people who have been vaccinated. Then Prosanta Chakrabarty (@LSU_FISH) continued the NiB tradition of blasphemy by explaing why creationism is not—and can never be—science. And finally, we announced that Nothing in Biology will be hosting the March 2013 Carnival of Evolution—you can see how to submit your evolution-related blog posts and other online content right here.

Then, over at the Molecular Ecologist, Tim Vines posted Molecular Ecology‘s first-ever list of top reviewers to provide some recognition for the volunteer labor that goes into a good peer-review process. And I wrote about a cool new study that goes looking for the “missing” heritability in quantitative trait locus studies—and finds a lot of it, with the help of lots of statistical power. (It turns out that a lot of the missing heritability is hiding in genes of small effect, which is exactly what some folks have long speculated.)◼

The Molecular Ecologist: Sexual selection, natural selection, and pronghorn

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Run antelope, run! Male pronghorn, on the run. Photo by Great Beyond.

Meanwhile, over at The Molecular Ecologist, I interviewed my old friend Stacey Dunn about a study of hers recently published in Science, which presents ten years of data to examine how A.J. Bateman’s principal of sexual selection — that males maximize their evolutionary fitness by mating with lots of females, but females maximize their fitness by mating with just one or a few carefully-chosen males — in pronghorn.

The National Bison Range pronghorn have been studied extensively by John [Byers] and his lab since 1981. Each spring, we captured nearly all fawns born in the population. During captures, we weighed, measured, sexed and tagged the fawns and took a tissue sample for genetic analysis. We genotyped each individual alive since 1999 at 19 microsatellite loci. We determined paternity for all fawns based on genotype. Maternity was known from fawn captures, but was also confirmed genetically. We then used that information to reconstruct a multi-generational pedigree of the pronghorn population.

To learn how the study improves on Bateman’s original work with fruit flies (which has since been called into question for methodological issues), and for Stacey’s tips on how to catch a baby pronghorn, go read the whole thing.◼

Nothing in Biology Makes Sense: Making sense of same-sex orientation in humans

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This week over at Nothing in Biology Makes Sense, I’m taking a look at a much-heralded new journal article that purports to solve an evolutionary puzzle that has particularly personal interest to me: how same-sex sexual orientation could evolve in the face of its selective costs. Of course, I’ve previously discussed a long list of possible answers to this question — but the new paper suggests that the best solution may lie in the epigenetics of sexual development.

Epigenetics is an appealing explanation for same-sex attraction because we have, at best, a fuzzy picture of the genetic basis of sexual orientation. Homosexuality definitely “runs in families”. That is, people with gay or lesbian parents, siblings, aunts, or uncles are more likely to be gay or lesbian themselves; and pairs of identical twins, who share pretty much all their genetic code, are more likely to have the same sexual orientation than pairs of fraternal twins, who share only half their genes.

Yet more sophisticated methods to identify specific genes associated with sexual orientation have failed to find any consistent candidates. (Though, as a caveat, the only genetic association study [PDF] I’ve seen suffers from small sample size and considers a very small number of markers by modern standards.) Moreover, while identical twins share sexual orientation more than fraternal twins, they don’t share it with complete fidelity — only about 20% of gay men who are identical twins have twin brothers with the same orientation.

For an explanation of what exactly epigenetics is, a full description of the new study, my evaluation of it all, and even some gratuitous — if, I hope, educational — beefcake, you’ll have to go read the whole thing.◼

The living rainbow: Er, kinda …

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06 Drosophila melanogater Mating Mating fruit flies. Photo by Image Editor.

I just saw this from Christopher Ryan, coauthor of Sex at Dawn, on Twitter:

Foundational Evolutionary Psychology paper called into serious question. Randy males/choosy females? Maybe not. npr.org/blogs/13.7/201…

— Christopher Ryan (@ChrisRyanPhD) December 13, 2012

As I tweeted in response: er, kinda.

Ryan linked to some new discussion of a study I covered back in June. That paper found a major flaw in a 1948 study of Drosophila fruit flies that was the first to clearly support a component of sexual selection theory — the idea that males maximize their evolutionary fitness (i.e., the number of offspring they sire) by having many mates, but females maximize fitness by selecting just a single “best” mate.

The author of the 1948 study, A.J. Bateman, tracked the parentage of flies in his study — which was necessary to tally the offspring of each male and female fly — using visible “marker” mutations. The new study’s authors, Patricia Gowaty et al., tried to replicate Bateman’s experiment, and discovered that some of the marker mutations were so disabling to the flies that they almost certainly biased Bateman’s results.

That knocks the legs out from under Bateman’s experiment. But it doesn’t really deal a knockout punch to sexual selection, much less to evolutionary psychology. Yes, evo psych (especially the kind that I really despise) tends to default to Bateman’s “randy males/choosy females” model. But evo psych, which is primarily about the recent evolutionary history of human behavior, isn’t the same thing as sexual selection theory, which is about the evolution of mating systems in, well, pretty much anything that reproduces sexually.

And, in fact, new studies with better data do support Bateman’s model for other non-human animals. Just a couple weeks ago, Science published a very thorough study on pronghorn antelope that tracked the interaction of Bateman-style sexual selection and regular old natural selection over a decade. (One of that study’s coauthors, Stacey Dunn, is a personal friend — I’ll be running an interview with her over at The Molecular Ecologist next week.) That work is based on modern genetic markers, which have none of the drawbacks of Bateman’s method.

But all of this is sort of beside the point, as far as the rightness or wrongness of evolutionary psychology goes, since fruit flies and pronghorn aren’t humans. There’s a huge diversity of sexual expression across the animal kingdom, and it’s absurd to think that we can make any particular conclusion about recent human evolution based on what works for insects or ruminants.

If evolutionary psychologists would be wrong to use Bateman’s fruit flies to support a particular hypothesis about human sexuality — and they would be — then those of us who disagree with them don’t have any reason to crow about Bateman’s mistakes.◼

References

Byers, J. & Dunn, S. 2012. Bateman in nature: Predation on offspring reduces the potential for sexual selection. Science, 338: 802–804. doi: 10.1126/science.1224660.

Gowaty, P.A., Kim, Y.-K. & Anderson, W.W. 2012. No evidence of sexual selection in a repetition of Bateman’s classic study of Drosophila melanogaster. Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1207851109.

Nothing in Biology Makes Sense: Making the jump from the mitochondrion

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SEM_mitochondria A mitochondrion. Photo by Jay Reimer.

This week at Nothing in Biology Makes Sense, Amy Dapper discusses co-blogger Devin Drown’s new study of the two not-quite separate genomes within every cell in your body:

Unlike our other organelles, mitochondria carry their own separate, circular genome. Furthermore, mitochondria are maternally inherited via the cytoplasm of the egg. This means that unlike the rest of the genome, the mitochondrial genome is inherited only from mom. Interestingly, over time, some of the genes that are important for the function of the mitochondria have moved from the mitochondrial genome to the nuclear genome.

That movement of genes from the mitochondria to the nucleus has some interesting evolutionary consequences, as you’ll find out if you read the whole thing.◼

Nothing in Biology Makes Sense: The rationality of science denialism

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Denial Photo by cesarastudillo.

This week at Nothing in Biology Makes Sense!, Sarah Hird delves into the psychology of science denialism to understand why facts alone can’t help a creationist:

Rosenau makes the case that when we (scientists/science supporters) talk to deniers/agnostics, conversations that begin in the scientific realm very quickly turn to religion, personal freedom, morality and even capitalism. The denial stems from how people identify themselves and how they see the world; it can be rooted in fear, anger and distrust of things outside their social group (religious and political affiliations are two major such groups). … The denial is not rooted in scientific facts.

To learn what does help denialists come around, go read the whole thing.◼