Thursday, November 29, 2018

I don't get it

Every week or so there are a flood of linked hits to Stones&Bones from porno sites.

I fail to see the connection. Any ideas in the multiverse?

Sunday, November 04, 2018

Archaic foolin' around

DNA sequencing studies starting in 2010 showed that there was interbreeding between H. sapiens, and Neanderthals (1). We also know that there was a third archaic human population known as the Denisovan, named from the Siberian cave where the first examples were recovered (2). They also interbred with modern H. sapiens, and at least occasionally with Neanderthals (3, 4). Finally, it has been shown that Neanderthals had a high amount of inbreeding, and more limited social and economic networks (4).

Modern humans all have H. sapiens mitochondria. Mitochondria are the cell organelles that make the “energy molecule” ATP. They also have their own DNA. So, for openers we know that no offspring from a Neanderthal female and a H. sapiens male mating later reproduced. It is even suggested that the female H. sapiens would be incapable of carrying a Neanderthal sired male fetus to term (5, 6).

Next, there are different descent patterns for the sex chromosomes labeled X, and Y. All females in our genus would have had 2 matched X chromosomes. Their eggs will always (in healthy examples) have an X chromosome. The males have one set of X, and one set of Y DNA. Sperm will carry (in healthy examples) one or the other.

So what does this say about the interbreeding behaviors of these 3 distinct human populations. First, the archaic humans were in decline even at the start of the modern human expansion out of Africa and into Eurasia. A massive glaciation event between 200, and 100 thousand years ago pushed the archaics into a terminal decline. And, as the moderns expanded, the archaic populations declined even faster.

(From Prüfer, 2014)

What we know is that no modern male successfully bred with a Neanderthal female. No female Neanderthal carried a fertile offspring from a modern male. We know that no modern female carried a successful male offspring sired by a Neanderthal male.

For those observed data to make a fairly easy social story, isolated Neanderthal males were adopted out of failing groups into modern human Hunter and Gatherer groups. They mated the modern females, and had a limited number of successful fertile female offspring. If the modern human female was a “captive” or what have you, her carrying any Neanderthal genes would have been lost.

1) Green RE, et al. A draft sequence of the Neandertal genome. Science. 2010;328:710–722.
2) Meyer M, et al. A high-coverage genome sequence from an archaic Denisovan individual. Science. 2012;338:222
3) Reich D, et al. Denisova admixture and the first modern human dispersals into Southeast Asia and Oceania. American journal of human genetics. 2011; 89:516–528.
4) Kay Prüfer, et al. The complete genome sequence of a Neandertal from the Altai Mountains. Nature. 2014 Jan 2; 505(7481): 43–49.
5) Ann Gibbons Modern human females and male Neandertals had trouble making babies. Here’s why Apr. 7, 2016.
6) Fernando L. Mendez, G. David Poznik, Sergi Castellano, Carlos D. Bustamante. The Divergence of Neandertal and Modern Human Y Chromosomes. American Journal of Human Genetics. April 07, 2016 Volume 98, ISSUE 4, P728-734,