Link parade, 2

3 minute read

Ben Phelan at Slate writes about the recent evolution of lactase persistence: “The Most Spectacular Mutation in Recent Human History”.

The plot is still fuzzy, but we know a few things: The rise of civilization coincided with a strange twist in our evolutionary history. We became, in the coinage of one paleoanthropologist, mampires who feed on the fluids of other animals. Western civilization, which is twinned with agriculture, seems to have required milk to begin functioning. No one can say why. We know much less than we think about why we eat what we do. The puzzle is not merely academic. If we knew more, we might learn something about why our relationship to food can be so strange.

I wanted to quote that passage because it was my friend Greg Cochran’s son Roddy who coined the term “mampires”, which is exceptionally clever. On the article as a whole, I think Phelan makes too much of the “mystery” aspect of the advantage of lactase persistence. There are really only two serious hypotheses and none of the possible explanations are mutually exclusive. I would have liked to see the article devote more attention to the multiple lactase persistence mutations in other populations, which together point to the very great advantage of the trait in association with dairying.

David Dobbs writes in the New York Times about the genetics of intelligence and what we know (and don’t know) about it: “If Smart Is the Norm, Stupidity Gets More Interesting”. The piece emphasizes that geneticists haven’t had much luck finding genes that explain the heritability of intelligence. The problem of “missing heritability” has loomed over complex trait genetics for the last several years, meaning that we can estimate the heritability of traits with twin studies and other traditional pedigree approaches, but single gene loci do not account for much of the variance of these traits. One possibility is that common genes have such small effects that they are statistically difficult to find.

Another possibility is that very rare genes of small effect – or new mutations – may explain the heritability of such traits within families. The most likely reason for large-effect mutations to be rare is if they are deleterious. Across a population, this hypothesis of many rare deleterious mutations is called “genetic load”:

But in some other genetic realms we do differ widely, for example, mutational load the number of mutations we carry. This tends to run in families, which means some of us generate and retain more mutations than others do. Among our 23,000 genes, you may carry 500 mutations while I carry 1,000.
Most mutations have no effect. But those that do are more likely to bring harm than good, Dr. Mitchell said in an interview, because there are simply many more ways of screwing something up than of improving it.

This is a nicely balanced treatment and emphasizes evolutionary approaches in an accessible way for Times readers.

From the San Jose Mercury News, a story by Lisa Krieger: “Open-source science helps San Carlos father’s genetic quest”.

One tiny flaw in one gene in one little girl. That explains why Beatrice Rienhoff, 8, is so lean and leggy.
No one else in her family had such a syndrome. In fact, apparently no one else in the world did either.
Rienhoff -- a biotech consultant trained in math, medicine and genetics at Harvard, Johns Hopkins and the Fred Hutchinson Cancer Research Center in Seattle -- launched a search.

Yes, you can do this now. This father is now making transgenic mice with his daughter’s mutation to better understand its effects.

(via Gene Expression)

Ken Weiss writes about some of the reasons a family medical history is a better predictor of individual health than genotyping: “23andLess”.

The most likely truth at this stage is that such common traits like heart disease or how tall or heavy you are, are determined by a very large number of genes, mostly with individually very small effects. Each person with the 'same' trait--each diabetic, say--has that trait for a different genetic reason. Individual genetic variants may be causal contributors, but they are not very important.

I agree with his point…although as I was reading the post, it occurred to me that doctors treat family history as if it were much more effective than it should be, if causal variants really have small effect sizes. Complex disorders are not the same as Mendelian disorders with low penetrance. Having a grandfather with heart disease, for example, should mean substantially less to you than having a grandfather who is tall.