The Lost World

A while ago I mentioned that there might be unrecognized survivors of South America’s local placental lineages (Meridiungulata and Xenarthra). Unrecognized because very divergent, like golden moles, which are Afrotheria. Shoot, maybe even metatherians or some relative of necrolestes.

But where to look? Tepuis might be good candidates. They’re remnants of a sandstone plateau that once covered the area between the north border of the Amazon basin and the Orinoco. These mesas are isolated from the surrounding forest and have lots of endemic flora and fauna. Some have almost constant cloud cover and have hardly been explored.

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Alte Kockers

For a long time we have known that longevity tends to increase with IQ. Obviously this was because smarter people paid more attention to medical advice – (“More Doctors Smoke Camels”, put your baby on its stomach). But maybe not. Recent work suggests that most of the variance in IQ is explained by rare deleterious variants – mutational load. If correct, it might be that smarter people have fewer screwed-up genes than average, and live longer because they’re in better genetic shape. Plausible, since most genes influence IQ.

Assume that is the case: all else equal, higher IQ means lower genetic load and greater longevity. Then a group with higher-than-average IQ might well live longer. The same selective forces that increased IQ would have decreased genetic load. Not that differences in genetic load have to be the only factor influencing IQ and longevity – chimps probably have lower genetic load than humans, because of their larger effective population size over the long term – but they’re still dumb and short-lived, compared to humans. For that matter, herring probably have even lower genetic load – it’s not enough.

Unless lox is nootropic, Ashkenazi Jews have probably experienced selection for higher intelligence. So probably they ended up with lower-than-average genetic load [not counting deleterious genes that became common by founder effect or by conferring heterozygote advantage for intelligence (or something other trait favored in their niche)].

Under these assumptions, Ashkenazi Jews should live longer. And they apparently do, judging from UK census info. “According to British census data, Jews live an average of five to six years longer than their gentile counterparts, and there may be nearly three times as many Jewish centenarians as in the general U.K. population.” “Barzilai and his colleagues reported in the Journal of the American Geriatrics Society that Jews who make it past 95 have dietary habits and levels of alcohol consumption and physical activity similar to their shorter-lived counterparts — suggesting that genes for exceptional longevity could do more than behavior to support long life.” “They were protected by their genes,” Barzilai said. “Not the environment.”

This can’t be the only thing affecting longevity. Time since since the agricultural transition probably matters. Long-term pathogenic exposure influences the strength of the immune response, which has side effects…

But if Ashkenazi Jews live longer than Italians or Levantines, you have to wonder if it’s caused by selection. Worth checking out.

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Interview: Cabbages and Kings

Part 1 of my new interview with James Miller is now up.

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Secondary response

After you’ve been exposed to a pathogen, antigen specific memory B Cells persist. If the pathogen reappears, they quickly pump out antibodies against that pathogen.

I have the impression that, when this happens, you can feel bushed. I’m not sure if that impression is correct, but it’s based on various times that I’ve been hanging around sick kids, doing things for them, without actually catching the flu or stomach bug they have. When I don’t catch it, seems likely it’s one that I’ve had before.

Does anyone know if there really is such a response?

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DARC matters

DARC (Duffy antigen receptor for chemokines) is a receptor expressed on red cells, key in the infection of those cells by vivax malaria. A version of the gene that eliminates expression of this receptor on red cells (and prevents vivax infection) has reached very high frequency (up to 99%) in sub-Saharan Africa. A new article in PLOS Genetics concludes that this was driven by some kind of strong selection, but a long time ago ( ~40,000 years). They estimate that the Duffy-negative mutation conferred a selective advantage of about 4.3%, leading to effective fixation in about 8,000 years. Not everywhere in Africa – didn’t happen in the Bushmen, Naturally they suspect that the selection was driven by vivax malaria , but they’re a bit mystified because today vivax is usually mild ( at last when compared with falciparum malaria). Vivax is often found in places where it can’t be transmitted year-round (because of winter) : it waits in the liver [hypnozooites] and reappears later, sometimes much later. I’ve heard of cases where it reemerged as much as 40 years later. Which means that it can’t afford to be too severe – it has to let the host survive.

However, in the tropics, it could get away with being more virulent, and perhaps it did, in the past.

An advantage of 4.3% is a lot, as selective advantages go, easily enough to drive a gene frequency from a tenth of a percent to 99% in a few thousand years. In much the same way, a behavioral tendency (heritable of course) that led men to have sexual intercourse with women other than their primary mate, when practical, could become very common even if it only resulted in a few percent extra surviving children per generation, say 2.2 instead of 2.1 . Compound interest. A behavior wouldn’t have to yield 100 extra children in order to become common (although producing an extra 100 would certainly have that effect!). In the same way, a heritable behavioral tendency that reduced the average number of offspring by a few percent would also become rare over a few thousand years.

What fraction of the practitioners in various human sciences understand this wee bit of population/quantitative genetics? Very few, I think.

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Ramble On

I’m raising money for another podcast with James Miller. I did one with him last year and had fun. Here’s the link. You can also send money via paypal, or bitcoins to 1Jv4cu1wETM5Xs9unjKbDbCrRF2mrjWXr5.

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Topics

I will probably be doing another podcast with James Miller soon. Suggestions are welcome. I’m considering reviewing more dreadful yet influential books and/or articles: readers have already suggested some, such as Jonathan Marks’ new book, and that article about twin studies in Slate. I would, I think, include books that are seriously wrong but not utter dreck. The candidates should include books that are not brand-new – I could diss The Republic, for example.
Name a book.

I will run gofundme or similar appeals for these efforts: I gotsta get paid.

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