When someone tells you that height is 80% heritable, does that mean:
a) 80% of the reason you are the height you are is due to genes
b) 80% of the variation within the population on the trait of height is due to variation of the genes
The answer is of course b. Unfortunately in the 5 years I’ve been blogging the conception of heritability has been rather difficult to get across, and I regularly have to browbeat readers who conflate the term with a. That is, they assume that if I say that a trait is mostly heritable I mean that its development is mostly a function of genes. In reality not only is that false, it’s incoherent. Heritability is addressing the population level correlation between phenotypic variation and genotypic variation. In other words, how well can genetic variation work as a proxy for phenotypic variation? What proportion of the phenotypic variation can be accounted for by genotypic variation? The key terms here are population level and variation (or technically, variance). We are not usually talking about individuals; and we are restricting our discussion to traits which vary within the population.
I’ve talked about menopause a fair amount on this blog, usually in relation to the Grandmother Hypothesis. So I thought I’d pass along this article, Eusociality, menopause and information in matrilineal whales, along. I know that many think that menopause is something that will naturally happen if a mammal lives long enough, as opposed to being an adaptation. I’m generally skeptical of this. The one physical anthropologist who I’ve talked to and who has explored the topic kept reiterating to me how contingent and interlocking the physiological cascades which shut down the reproductive cycle were. In contrast males tend to exhibit less fertility over time as their body just breaks down with age. Finally, of course it seems that even if there was some physiological process which would result in menopause if life history was pushed far enough down the line, over time adaptations should mask such enforced sterility (e.g., a new genetic variant which masks this phenotype).
Update: Comment from Chris Surridge of PLOS One:
Just a quick note. The paper is now formally published on PLoS ONE. The citation is:
Tuljapurkar SD, Puleston CO, Gurven MD (2007) Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan. PLoS ONE 2(8): e785. doi:10.1371/journal.pone.0000785
As it is PLoS ONE you can rate the paper, annotate and discuss it there too.
There’s a new preprint posted (PDF) on PLOS One titled Why Men Matter: Mating Patterns Drive Evolution of Human Lifespan. The basic question is this: why do humans live beyond the lifespan of the post-menopausal female, about ~55 at the outer bound? You might ask, “Why not?” As alluded to in the paper there is the problem of antagonistic pleiotropy, mutations which favor fertility early in life with a trade off of heightened mortality past reproductive age should always be favored. Over time these mutations would build up and there should be a “Wall of Death” past the age of 50 as these accumulated mutants manifest themselves.
…The best-fitting model indicated that 55%…of the variance in the 2- to 9-year-olds’ prosocial behaviour was due to genetic factors and 45%…was due to non-shared environmental factors. It is concluded that genetic and environmental influences on prosocial behaviour in young South Koreans are mostly similar to those in western samples.
This is the “standard” finding, most of the variation in behavior is due to genes or non-shared environment. In The Nurture Assumption Judith Rich Harris posited that the “non-shared environment” basically meant peer groups. Remember though that this is measuring a component of variance, so it applies to traits which vary throughout a population.
I was talking with a friend of mine who is an economist about science, and the great productivity in modern societies which allows for the perpetuation of narrow specialties in scholarship. I repeated to him my own hunch that if all scientists who were alive today disappeared and the next generation of aspiring scholars had only books and other instructional materials to go on, science would simply disappear as an enterprise. The point I was trying to get across is that scientific ideas are contingent upon a particular cultural framework. That is, science is a culture. And that culture is embodied in living human beings.
Over at my other blog Herrick posts a response to 10 questions for Gregory Clark. Clark is an economic historian whose most recent book Farwell to Alms is making a splash. I read the book recently, but because I’m not well versed in economics I’ve held off saying much. I will add that Clark’s point that the typical humans of 1800 were poorer and less well off than those of 10,000 BCE is an important insight, and it is born out by decades of analysis of remains which show that farmers are on average underfed and nutrient deprived vis-a-vis hunter-gatherers.
Check out this new interview with Steven Pinker. It ostensibly focuses on his new book, The Stuff of Thought, though it covers a lot of ground. My own feeling is that the interviewer should have let the focus be more on Pinker than his own pet theories, but there’s a lot of good stuff in there.
Yesterday I posted on the resurrection of the “redheads going extinct” meme (as I noted, this story seems to cycle every few years). The current source is National Geographic Magazine, which doesn’t have the “article” online. I went to the bookstore and checked out the September 2007 issue, and a write up does exist about the redheads going extinct. Unlike the secondary sources it isn’t as sensationalist, and makes more than a passing nod to the Hardy-Weinberg logic from which the inference is derived.
That being said, the write up in National Geographic Magazine simply recycles older versions of this story which emerged a few years ago, and doesn’t add any new “data” or analysis. In other words, we have here a staffer who needed a short paragraph or two to fill up a page in National Geographic Magazine, so they googled around (or something that effect), and simply repeated claims made in the previous rounds of reportage. As I noted earlier, those claims were pretty much made up. So you have here a case where a non-story from a few years ago was picked up by National Geographic, and the imprimatur of such a high status publication repeating the story has resulted in the reemergence of the meme in the venues which originated it in the first place!
In any case, the numbers which are injected to add a layer of scientific plausibility were likely concocted by the original writers who repeated the meme. I am skeptical that even 1% of the world’s population has red hair; people of European descent form around 15% of the world’s population last I checked, so such a high world wide frequency implies that around 1 out of 10 people of European descent is a redhead. Doesn’t pass the smell test.
Check it, Chris Mooney is on bloggingheads.tv. He’s promoting his book Storm World, which is a really good read. I can’t speak in detail to the area of science which Chris covers, but the bigger picture issue of the “intersection” between public policy and the culture of science and the ensuing controversies have a universal resonance.
p-ter points me to a new paper which documents interspecies hybridization in monkeys whose lineages putatively diverged about 3 million years ago. Note that the hybridization follows Haldane’s rule: the heterogametic sex (in mammals the males) exhibits sterility while the other sex does not. Whatever genetic incompatibilities built over the period during which the two populations became distinct the less robust sex (males have only one copy of the X chromosome, ergo, sex-linked diseases) naturally exhibits greater breakdown in hybrids. In any case, the story is obviously relevant to Neandertal introgression, since the divergence between moderns and Neandertals is on the order of 1 million to 100,000 years.
Related: Mammalian hybridization potentialities.
Every few years it seems that a new meme declares that “blondes will go extinct!” or that “red hair will go extinct!” I’ve only been blogging for 5 years, and this story has already cycled multiple times. A co-blogger of mine told me that he did some digging and it seems that this meme is of old vintage, with “blondes going extinct!” stories dating back to the 19th century. The current craze (as evidenced by blogs) seems to have started at an Australian newspaper. But, it is sourced originally to National Geographic Magazine.
First, the story doesn’t appear on National Geographic Magazine’s website that I can tell. Perhaps it is in the print issue? A reader who has a copy of the current issue might want to post their finding in the comments (I will probably go the bookstore tomorrow and check myself). Let’s assume that the story is correct. What are they actually trying to say here? They are actually just restating inferences derived from the Hardy-Weinberg Equilibrium in a panmictic population; this isn’t really a “discovery.” Let me clarify what I mean.
RPM pointed me to this new paper, Major Histocompatibility Complex Heterozygosity Reduces Fitness in Experimentally Infected Mice:
…Our results show that MHC effects are not masked on an outbred genetic background, and that MHC heterozygosity provides no immunological benefits when resistance is recessive, and can actually reduce fitness. These findings challenge the HA hypothesis and emphasize the need for studies on wild, genetically diverse species.
This is more of a quick note than a post. In Africa (and to a lesser extent other regions) the rise of malaria has resulted in an extreme evolutionary response, basically the heterozygote is extremely fit vis-a-vis mutant homozygotes (which exhibit Sickle Cell Anemia) and the wild type homozygotes. This is a case of balancing selection via overdominance, the frequencies of the alleles are determined by the fitness of the three genotypes (mutant homozygote, heterozygote and wild type homozygote). Naturally polymorphism will be maintained since the heterozygote by necessity needs the maintenance of genetic diversity to perpetuate its existence. It seems likely that this sort of adaptation is a short term response to extreme evolutionary pressures. If this flavor of heterozygote advantage was ubiquitous the segregation of homozygotes on so many loci would result in an implausible variance in fitness. It seems likely that over time evolution will come up with a less extreme adaptation, perhaps modifying the mutant allele in the case of malaria with other mutants which mask the deleterious impact of Sickle Cell Anemia.
This morning in NYC I took a cab to Penn Station. It was raining really hard…so I was curious, I asked the cab driver, “So do you get more fares when it’s raining?” He explained that yes, there are more fares on hand, but because of the rain and traffic jams it works out to less revenue in a given day (e.g., he explained that half the time he’s stuck in traffic without a fare).
Then I showed up in D.C. this afternoon, and I notice no meter or even all that offical crap that NYC cabs have. I start freaking out and wondering whether this is really a cab, but the guy drops me off and asks for a reasonable amount. Later I find out that D.C. has some “zones,” instead of metered service. Strange.
Most of you know that I was in NYC this weekend and I hung with the ScienceBlogs crowd. Others have summarized the goings on with eminent competence, so I won’t add more to that. There was lots of fun to be had, and I made sure I had some of it. But, I would like to give a shout out to two individuals: Lee Billings and Joshua “I like it brown!” Roebke. They’re editors at Seed, and really fun guys when drunk/drinking. I do have to say that my memories are pretty pleasant since I schooled Roebke in a “Yo Mama!” face off, nerd style. He likes it dead and brown; that’s all you have to know. As for Billings, he’s a chill guy whose passion for the space program I sympathize with. The editors at Seed aren’t just word smiths, they’re fully rounded humans beings who like to drink beer.
P.S. And Orac, I hope someone finally told you I am not Scientific Indian.
I went to Bacchus on Atlantic Avenue in Brooklyn tonight. Great food, great wine. But here is why I am giving them props: habanero tabasco sauce!. Yes, instead of offering me cayenne tabasco, they actually offered me a nice spicy condiment. And I shall remain eternally grateful. So:
409 Atlantic Ave
Brooklyn, NY 11217-1702
Phone: (718) 852-1572
Check it out. And ask for hot sauce!