Photo by blmiers2.A new edition of the Carnival of Evolution is online over at The Atavism. Highlights of the monthly roundup of online writing on all things relating to descent with modification include John Wilkins on evolutionary novelty, Anne Buchanan on disgusting evolutionary storytelling, and Bjørn Østman on Michael Behe. Also represented: recent work from this blog, and from Nothing in Biology Makes Sense!. Go check it out! ◼
Evolution can make leaps—but how frequently? Photo by Flavio Martins.
Does evolutionary change happen in big jumps, or a series of small steps? The question may seem a little esoteric to non-scientists—how many mutations can dance on the head of a pin?—but it has direct implications for how we identify the genetic basis of human diseases, or desirable traits in domestic plants and animals.
That’s because the evolutionary path by which a particular phenotype, or visible trait, first evolved in a population is closely related to the genetics that underlie the trait in the present. Phenotypes that arose in a single mutational jump will probably remain connected to one or a few genes with large effects; phenotypes that evolved more gradually do so because they are created by the collective action of many genes. So what kind of evolutionary change is most common will determine which kind of gene-to-phenotype relationships we should expect to find.
In an excellent recent review article for the journal Evolution, Matthew Rockman, a biologist with the Department of Biology and Center for Genomics and Systems Biology at New York University, makes the case that the era of genomics has, so far, been much too focused on finding genes of large effect. Fortunately, Rockman also sees the beginnings of a new movement towards acknowledging the importance of small-effect genes—one which may ultimately make genomic association studies more useful.
Experimental evolution of multicellularity. Photo by Nothing in Biology Makes Sense!In this week’s new post at the group blog Nothing in Biology Makes Sense!, Sarah Hird discusses the recently published experimental evolution study that used laboratory yeast to tackle one of the biggest questions in reconstructing the history of life:
Some of the biggest questions in evolutionary biology deal with the origin of life. For example, if I go back one generation, I find my parents. Two generations, my grandparents. Ten generations are human beings who may or may not have looked like me. Five hundred thousand are, oh, I don’t know. Maybe a bipedal hominid? Anyway, if we continue going backward like this, we inevitably get to time zero and encounter some big-time questions that can really cause a brain to cramp up.
I promise you, if you read the whole thing, you will not experience brain cramps. Quite the opposite, in fact.
In other news, Nothing in Biology Makes Sense! has put out a call for guest contributors. If you work in biology—anything from medicine to plant breeding—and you’ve been thinking about giving this science blogging thing a try, send us an e-mail!  ◼
Story time. Photo by McBeth.Over at Neuroanthropology, Greg Downey’s launching an ambitious project: making evolutionary psychology less … shitty.
More specifically, and more politely, Downey thinks (as I do) that evolutionary biology can tell use some valuable things about human nature; but he’s concerned (as I am) that the most visible representatives of an academic field which takes the evolution of human nature as its central question often apply an impoverished understanding of evolutionary biology to telling titillating (and usually unsubstantiated) adaptive fairy tales. Which fairy tales all seem to take place in a sort of dark Lake Wobegon, where all the women are weak and choosy, all the men are strong and horny, and children are barely more than notches on the bedpost of natural selection.
Against the strong man/choosy woman story, Downey proposes the “long, slow sexual revolution.” The central idea is that, as our ancestors’ intelligence increased toward modern humanity, their interest in, understanding of, and uses for sex and sexuality changed:
The idea of the ‘long, slow sexual revolution,’ I think, provides a simple and balanced umbrella for pulling together contradictory elements of our sexuality, gender relations, and reproductive strategies. Everyone knows that the more recent ‘Sexual Revolution’ didn’t erase pre-existing sexual mores and patterns, but rather mixed with them, producing a conflicted, sometimes-unpredictable pattern of sexual expression. Starting with a ‘sexual revolution’ rather than the Men-are-from-Mars-Women-are-from-Venus story means less erroneous leaping to stereotypes to undo when we teach or communicate about human evolution. [Emphasis sic.]
In one of many insightful points, Downey draws in Emily Willingham’s recent post on family planning before the Pill—humans have had the intelligence, and the means, to use sex for more than making babies since (probably) before the dawn of recorded history.
That’s really only the jumping-off point of a post that delves deep into the problems of evolutionary psychology and what might be done about them. And it’s the first part in a promised series! So go read the whole thing, and keep an eye out for future installments. I’ll certainly be watching with interest. ◼
Lignum vitae est. Photo by Niels Linneberg.Whoops. I totally failed to point out that the latest Carnival of Evolution is up at The EEB & flow. With bonus historical perspective:
523 BCE
Anaximander: “Thales, my teacher, how is it that animals take their form?”
Thales: “Anaximander, all matter is an aggregation formed from a single substance, water, and qualities are obtained through need”
Anaximander: “Ah yes, water, I will now think about how air can be the primordial substance.”
Fortunately, there’s also lots of much more recent material, which is the whole point of a monthly compilation of all things online and evolution-related. Included are a couple of my latest posts, and Luke Swenson’s great post (for Nothing in Biology Makes Sense!) explaining how biologists can trace the evolutionary past of an HIV infection to identify its source. Go take a look, if you haven’t already. ◼
Photo via Octopus Overlords.I have a history with Jesse Bering’s evolutionary psychology writing, and I do, in fact, have better things to do over the holidays than deal extensively with his latest offense against evidence-based reasoning. But this one is pretty egregious: Bering pretends to be an advice columnist counseling a (hopefully imaginary) “hebephile” that there is a perfectly good adaptive explanation for lusting after “very young girls,” even if our insufficiently evolution-conscious society frowns on it. Oy.
Bering cites a previous column arguing that attraction to young adolescents could be adaptive because youth correlates with fertility. Said column is conspicuously devoid of biological data. However, five minutes with Google found me an abstract that puts the age at which women’s fertility is up to full adult capacity at about six years after their first periods. Given an average age of menarche at 12.5 years, that means it should be most adaptive to lust after, um, 18- to 19-year-olds.
Of course, there are also all sorts of environmental and cultural factors to consider—that second paper I cited above is a study suggesting that increased obesity may lead to earlier onset of puberty. There’s also the question of whether there’s a genetic basis to finding a particular age cohort attractive, and whether the expected gain in reproductive output associated with attraction to women at exactly their age of peak fertility is enough to overcome genetic drift. Modern biology has data and understanding to apply to all these questions, but Bering can’t seem to be bothered to mention any of it.
That’s just my small, late-coming contribution to a great deal of variously outraged, thoughtful, and exasperated criticism of the “hebephile” column. Stephanie Zvan provided the letter-writer with a much better answer, Janet Stemwedel eviscerated Bering’s logic, and Isis the Scientist went straight for the jugular. The Journal of Are You Fucking Kidding Me pulled out its evo-psych BINGO card, and Chris Clarke went full-on Swiftian, as did Michael Eisen in a comment on Isis’s post.
If we get a response from Bering, I expect it’ll to be in line with his tweeted answer to critics and his previously demonstrated inability to do anything other than double down on whatever he’s already said. My assessment, which isn’t new, is that Bering’s writing strongly suggests he’s not interested anything so boring as what we can deduce from actual evidence. Especially if it would get in the way of a nice, juicy headline.
I certainly can’t prevent Bering doing whatever brings in the page-views, but I do wish he’d stop calling it “science.” ◼
A male greater honeyguide. Photo via Safari Ecology.Brood parasitic birds lay their eggs in other birds’ nests, a lazy approach to parenting that shapes the behavior and evolution of brood parasites in all sorts of interesting ways.
Brood parasite chicks often kill their adoptive nestmates, and can grow up confused about their species identity. To better trick their hosts into accepting “donated” eggs, many brood parasites have evolved eggs that mimic the hosts’—and some hosts have evolved contrasting eggs in response. A recent genetic study now shows an even subtler pattern arising from this host-parasite coevolutionary chase: lines of parasitic females that have specialized on the same host species for millions of years.
The brood parasite in question is the greater honeyguide, an African bird best known for helping people find bee colonies (though the story that honeyguides also guide honey badgers don’t have much factual basis). However, honeyguide females also lay their eggs in the nests of several host species—including hoopoes, greater scimitarbills, green woodhoopoes, little bee-eaters, and striped kingfishers. Although the honeyguides’ eggs aren’t colored like their hosts’, they do have matching shapes—the hosts all nest in tree cavities, where lighting is too poor to notice a mis-colored egg, but an oversized or oddly shaped one would stand out.
A hoopoe, one of the birds that “adopts” greater honeyguide eggs. Photo by Hiyashi Haka.There’s an evolutionary catch, though: hoopoes, scimitarbills, and woodhoopoes lay oblong eggs, while the bee-eaters and kingfishers lay spherical eggs. Yet honeyguide females manage to lay eggs of matching shape and size in the nest of each host. Individual brood parasites can’t adjust the shapes of their eggs to match those in a host nest—they find hosts with eggs that will match their own.
How do they do it? Maybe each female honeyguide actually goes looking for nests like the one she grew up in, either because she is compelled to by some genetic instinct, or because she learns to recognize a potential host in the course of being raised by that host. Or maybe the host birds are so good at recognizing and rejecting oddly-shaped parasite eggs that only well-matched eggs make it to adulthood. Any of these processes could result in long lineages of female honeyguides laying eggs in the nests of the same host species their mothers, grandmothers, and great-grandmothers used. This is precisely the pattern Claire Spottiswoode and her coauthors found in the population genetics of greater honeyguides.
Spottiswoode et al. collected genetic data from honeyguides using all five of the host species mentioned above, and compared the patterns of relatedness from different genetic markers to patterns of host use. The pattern of differentiation in a marker from the mitochondrial genome—genes contained in the mitochondria, which mothers pass on to their offspring but fathers do not—neatly divides the honeyguides between hosts with oblong eggs and the hosts with spherical eggs. By applying a molecular clock to the mitochondrial data, the team found that the division between oblong-egg and spherical-egg honeyguides dates back as long as 3 million years ago. So honeyguide females have been tracking the same hosts, or very similar ones, for quite some time!
However, no such pattern is evident in four genetic markers from the nuclear genome, which is inherited via both parents. That suggests male honeyguides don’t discriminate among females based on host fidelity—mates pair off regardless of what host species they each grew up with. Spottiswoode et al. also note that this result hints at how honeyguide egg characteristics and host preferences could be inherited: via the female sex chromosome. In birds, biological sex is determined by the Z and W chromosomes—individuals with two Z chromosomes develop as males, and individuals with a Z and a W chromosome develop as females. Host preferences and egg shape inherited via the W chromosome would then be carried only by females.
However, the data presented here don’t directly test the W-chromosome hypothesis. That would require markers—or better yet complete sequence data—from the W chromosome itself, and (to be really thorough) lots more markers from the rest of the nuclear genome as well. That’s a lot of genetic data to collect, but we are very close to the day when such data are easily collectible. ◼
Reference
Spottiswoode, C., Stryjewski, K., Quader, S., Colebrook-Robjent, J., & Sorenson, M. (2011). Ancient host specificity within a single species of brood parasitic bird. Proc. Nat. Acad. Sciences USA, 108 (43), 17738-42 DOI: 10.1073/pnas.1109630108
The molecular structure of HIV. Photo by PHYLOMON!.In the latest post at the group blog Nothing in Biology Makes Sense!, contributor Luke Swenson describes how biologists can reconstruct the evolutionary history of HIV to estimate when the virus make the jump from chimps to humans, or even when a single patient became infected.
Although HIV evolves rapidly, it does so at a fairly constant rate. In essense, you can use this constant rate to act like a clock to tell you roughly how many changes accumulate over a year. Then, by figuring out the number of changes it would take for both sequences to converge on a single identical sequence (their most recent common ancestor, “MRCA”), you can get an estimate of the date that the MRCA existed at.
This is one of the best cases I know about in which evolution directly informs medical practice and treatment, and it’s well worth reading the whole thing. ◼
Forty-two. Photo by Valerian Gaudeau.The new Carnival of Evolution, freshly posted over at the Ocelloid, is the forty-second iteration of the monthly roundup of online writing about evolution, the universe, and everything. Well, maybe not everything.
Highlights include, but are not limited to, Larry Moran illustrating the difference between census population size and effective population size, Hannah Waters on the evolutionary context of grieving, and Jenna Gallie’s description of her own research on rapid adaptive evolution by E. coli. There are also multiple contributions from Nothing in Biology Makes Sense!, in case you haven’t already seen them. Go read the whole thing, and don’t forget your towel. ◼
A peacock, which made Darwin “sick.” Photo by aussiegal.This week at the collaborative blog Nothing in Biology Makes Sense!, guest contributor Tom Houslay makes sense of costly mating displays:
Time and again in the animal kingdom, we see exaggerated ornaments, vibrant colours, and fantastic acoustic and visual displays. Frogs and crickets advertise their whereabouts with loud calls, fireflies flash patterns with bioluminescence; greater sage grouse strut brazenly in open pastures. While they undoubtedly brighten up the world around us, these behaviours and morphologies can seem not only unnecessary, but downright detrimental to the survival of an individual. How, then, can their existence be resolved with our knowledge of evolution?
To find out how a single showy trait can come to “capture” all the genetic variation in a population, read the whole thing. On an almost totally unrelated note: if I ever open a gay bar, it will definitely be called Lek. ◼