Just How Hot Is That Red Hot Chili Pepper?.

Update: Another post on this topic at my other blog.

A few days ago I pointed to a new paper, Evidence of Still-Ongoing Convergence Evolution of the Lactase Persistence T_-13910 Alleles in Humans. Knowing my interest in the topic you might assume that I would be "all over this." Well, I finally read the paper (twice) and I have to say it's a really interesting piece of work.

To the left is a map of the proportion of the T_-13910 SNP near the LCT locus in selected populations. In Eurasia the correlation between this allele and "Lactase Persistence" (LP) is very strong (r ~ 0.97 in terms of LP phenotype and frequency of T_-13910 with a p of less than 0.001) . Functional studies have shown that the presence of T_-13910 results in the maintenance of transcription of the enzyme which breaks down lactose sugar in milk. The phenotype is interpreted in the "dominant/recessive" model, one copy of the allele is all that is needed to be in a state of LP. So, if a population has a 0.50 proportion of the LP conferring allele, via the Hardy-Weinberg Equilibrium we know that 75% of the population exhibits the LP phenotype. A close look at the map shows us a few things. First, the allele of interest is modal in northern Europe. That is, its frequency is the highest there. This is no surprise as LCT has some of the strongest signatures of selection within the genomes of Europeans studied so far (the longest "haplotype block"). But, do note that the LP conferring allele is found throughout western Eurasia, and even into into nothern Africa. Though it is most frequent in northern Europe, that does not necessarily mean that the T_-13910 arose there.

/. has a post with the title Humanity's Genetic Diversity on the Decline, drawing from a recent paper which found that the mtDNA haplotype diversity in England was lower than 1,000 years ago. The authors were surprised because of course one presumes England is more cosmopolitan today than in the past, and so there would be more diversity. As a resolution to their finds they suggest that demographic dynamics, such as the Black Death with resulted in the death of 1/2 of the English in 1 generation, as well as selection for mtDNA variants (i.e., a haplotype is linked toward some functional benefit which increases its frequency within the population). One might also note that England has gone through massive population growth, and this has not always been equitable. In other words, the demographic explosion of the last few centuries might have been biased toward particular regions or segments of the English population, and reproductive output might have varied a great deal more than the common poisson assumption.

The New York Times has an article up reiterating the fabled "bushiness" of hominid phylogenetic trees:

Scientists who dated and analyzed the specimens -- a 1.44 million-year-old Homo habilis and a 1.55 million-year-old Homo erectus -- said their findings challenged the conventional view that these species evolved one after the other. Instead, they apparently lived side by side in eastern Africa for almost half a million years.

My knowledge of bones is not strong, so I leave it to John Hawks or Kambiz to decompose the details. That being said, the big picture is that this is another strike against anagenesis for the human lineage, which basically is a scientific concept expressed in the famous t-shirts showing a progression from ape to ape-man to Neandertal to modern human. Anagenesis easily slots into human cognitive biases such as the "Chain of Being," and I don't know how revolutionary it is to bury it again for the thousandth time. All that being said, it is a little irritating to see this bit of pop-evolutionary thinking crop up near the end of the piece: