Over at Nothing in Biology Makes Sense
, Chris Smith has been writing a series of posts digging deep into the evolutionary claims made in Nicholas Wade’s book A Troublesome Inheritance
. Last week, Chris debunked
the claim that human population genetics naturally sorts into “races”—this week, he’s taking on
Wade’s claim that variation at a particular gene has made some human populations more prone to violence than others:
Although some studies have found genetic variants in the MAO-A promoter region that are more common in some ethnic groups than in others (Sabol et al. 1998; Widom & Brzustowicz 2006; Reti et al. 2011) it is likely that these genetic variants are not –on their own– associated with violent or impulsive behavior (Caspi et al. 2002; Widom & Brzustowicz 2006). Instead, genetic variation in the MAO-A promoter seems to make some children less able to recover from abuse and childhood trauma, and therefore more likely to act out later in life (Caspi et al. 2002; Widom & Brzustowicz 2006). Simply carrying the ‘low expression’ allele in the MAO-A promoter does not have any effect at all on impulsivity or aggression.
Chris co-teaches a class on exactly the topics covered in A Troublesome Inheritance, so I highly recommend you read the whole thing, and follow the series to its conclusion.
I’ve written (another) review of Nicholas Wade’s “science of race” book A Troublesome Inheritance, this time for the Los Angeles Review of Books. If you’ve read the my previous review for The Molecular Ecologist, you won’t find much new here, but the LARB piece is pitched at a less technical audience, and takes a somewhat different point of entry:
CHARLES DARWIN is more usually cited for his scientific discoveries than his moral insights. In the closing pages of his travelogue The Voyage of the Beagle however, he condemns the practice of slavery — which he observed firsthand in the colonized New World — in blistering, heartfelt terms worthy of an Old Testament prophet
In this testimony against the great social sin of his age, Darwin makes an observation that should unsettle us even here and now: “if the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin.”
I’m extremely pleased for the chance to contribute to a great literary magazine, and I’m also quite happy to see that LARB went with my suggested, punny headline: “Cluster-struck.”◼
Over at The Molecular Ecologist I’ve done an in-depth review of the population genetics data cited by Nicholas Wade in his book A Troublesome Inheritance, which argues that social, cultural, and economic differences between human populations are all in our genes. Digging into the book’s endnotes, it didn’t take me long to find discrepancies between Wade’s description of basic population genetic results and the actual, um, results.
First and foremost, Wade claims that when population geneticists apply a class of statistical methods called clustering algorithms to datasets containing hundreds or thousands of genetic markers, they objectively identify five geographic groups that he calls “continental races”—differentiating African, European/Middle Eastern/South Asian, East Asian, Oceanian, and American people. What he does not make particularly clear is that while clustering methods do group genetic samples without direct instructions, the algorithms do not decide how many clusters there are. The geneticists using them do.
To make me feel somewhat better for having paid actual money to read this book, go read my whole review.◼
This week at Nothing in Biology Makes Sense!, guest contributor Daniela Vergara explains how CGRI, the initiative to sequence the genome-wide genetic variation of Cannabis, will answer cool evolutionary questions.
At the CGRI, we would like to understand first, how much genetic variation there is in the numerous pure C. sativa, C. indica, and C. ruderalis accessions and heirloom varieties. This will lead us to understand the relationships among the major lineages within the genus, the spread of Cannabis throughout the globe, and rates of historical hybridization between the named species.
For Daniela’s detailed run-down of important evolutionary questions in Cannabis, go read the whole thing.◼
Pollinator at work. Photo by jby.
Over at Nothing in Biology Makes Sense! I’m discussing pollination syndromes—suites of traits held in common by plants that use similar pollinators.
- Bee-pollinated flowers are usually blue or yellow, often with contrasting “guides” that point towards nectar rewards, and they usually have some sort of scent.
- Bird-pollinated flowers tend to be red and tubular, and often open downwards. They produce lots of relatively weak nectar, and generally don’t have very strong scents …
- Moth-pollinated flowers are usually white, opening in the evenings, and strongly scented.
To find out how evolution makes sense of these handy rules of natural historical thumb, go read the whole thing, and check out the new meta-analysis of pollination syndromes that I discuss.◼
At Nothing in Biology Makes Sens, Sarah Hird explains some of her own research, recently published at the journal Heredity, which documented just how “leaky” species boundaries can be in the chipmunks of western North America.
While doing a comparative phylogeography study, the Sullivan lab discovered that one particular subspecies, T. a. canicaudus, had a mitochondrial genome that was most closely related to the red-tailed chipmunk (T. ruficaudus), instead of the other yellow-pine subspecies. Additional data show that the T. a. canicaudus nuclear genome is in fact most similar to other yellow-pines – it’s just that the mitochondria is of red-tailed origin.
For all the sordid phylogenetic details, go read the whole post, and check out the original paper.◼
Over at The Molecular Ecologist I’m discussing a new paper in the journal Genetics, which demonstrates that selection acts more strongly on genes that affect multiple traits:
Genes that have roles in multiple traits—pleiotropic genes—have long been thought to be under stronger selection as a result of those multiple functions. The basic logic is that, when a gene produces a protein that has a lot of different functional roles, there are more functions that will be disrupted by changes to that protein. Which would be more inconvenient: if your smartphone suddenly needed a new type of power connector, or if every electrical outlet in your house suddenly accepted only plugs with four prongs?
A team at the University of Queensland tested this idea using a lot of fruit flies and some cleverly applied gene expression resources. To find out how it all worked, go read the whole post, and check out the original paper.◼
Over at The Molecular Ecologist, we’re continuing last week’s examination of anonymity in peer review with comments from our readers. A number of folks sent in thoughtful remarks in favor of anonymous peer review:
I’ve actually done an entirely open review [for Faculty of 1000] and I found the whole experience rather jarring; I wouldn’t have done it if I didn’t already like the software in question, and I think that could be unethical. Scott’s a nice guy and a good scientist; I’m not certain I would have been viewed very favourably being one of the first people to criticise the work of another in the open, despite the fact I think such a system has a number of benefits.
And likewise, in favor of signed reviews:
I do think reviewers should be disclosed on publication in order to get credit for their job, but also to take responsibility of it. In general, I also think signing makes the process more transparent and helps engage in a constructive conversation.
There are some excellent points made on both sides, and I recommend reading the whole compilation of views for and against anonymity.◼
This week at Nothing in Biology Makes Sense! I’m discussing a new study that purports to demonstrate that three-toed sloths are in a nutritional mutualism with specialized moths, fueled by algae and poop:
Sloths’ coarse, shaggy fur accumulates its own little microcosm of living passengers. (If you move that slowly in a tropical forest canopy, you’re going to get some hop-ons.) Among these are an assortment of algae, and moths in the genus Cryptoses. It’s been known for a long time that Cryptoses moths lay their eggs in sloth dung, and that their larvae eat it.
To find out why it isn’t completely crazy to think that these poop-eating moths might be helpful to sloths, go read the whole thing.◼
Over at Nothing in Biology Makes Sense!, Amy Dapper discusses a new study of brood parasites, birds that lay their eggs in the nests of other bird species, letting those adoptive hosts take on the costs of raising the brood parasites’ chicks. This sounds like a bad deal for the host species, but in at least one case, it turns out that a brood parasite chick can be a boon to its adoptive nest-mates:
Canestrari et al. (2014) focused on the great spotted cuckoo (Clamator glandarius) and their host, carrion crows (Corvus corone corone). They studied the success rate of nests with and without brood parasitism and found that carrion crow nests that contained parasitic cuckoo nestlings were actually more likely to be successful (i.e. fledge at least one crow nestling). How could this be?
To learn why a carrion crow might want to raise a baby cuckoo, go read the whole thing.◼