I have been reading David Reich's Who We Are and How We Got Here: Ancient DNA and the New Science of the Ancient Past.  Svante Pääbo and his colleagues at the Max Planck Institute developed techniques for extracting DNA from very old bones.  One of his early apprentices was David Reich, who established a lab at Harvard and has "industrialized" those techniques (his description) and since produced a huge portion of all the analyzed ancient DNA.  His new book is about those methods but mostly about the surprising facts that they have revealed about our ancestry.  Perhaps the most surprising fact is that nearly all human populations have been formed by repeated large scale mixing events.

Today the population of western Eurasia is relatively homogeneous, but 14000 years ago, the area was occupied by at least four distinct populations as different from each other as modern Europeans are from modern East Asians, according to Reich.  Modern Europeans are a mixture of those four…

Chick Shortage

The two big cultures on the most populous continent both prize males above females. Modern medical technology permitting sex selective abortions turned this age old preference into a major undersupply of females in the population. The Straits Times has a big story on it.

A combination of cultural preferences, government decree and modern medical technology in the world's two largest countries has created a gender imbalance on a continental scale. Men outnumber women by 70 million in China and India. The consequences of having too many men, now coming of age, are far-reaching: Beyond an epidemic of loneliness, the imbalance distorts labour markets, drives up savings rates in China and drives down consumption, artificially inflates certain property values, and parallels increases in violent crime, trafficking or prostitution in a growing number of locations. I found the story interesting throughout, but I want to focus on just one aspect.  The shortage of women has driven up savin…

The DNA Shuffle

We inherit half our DNA from each of our parents, but that DNA is shuffled in a couple of ways before we get it. This results in our inheriting our parents DNA in roughly 118 separate segments. That number increases by about 71 segments for each additional generation. The number of our ancestors, or at least the number of slots in our family tree, though, doubles every generation. Consequently, by the time we get to the tenth generation, we inherit about as many segments as we have ancestors, and by the twentieth generation, only about 0.1% of our genealogy actually contributes DNA. David Reich: Yet even if the genealogies are accurate, Queen Elizabeth II of England almost certainly inherited no DNA from William of Normandy, who conquered England in 1066 and who is believed to be her ancestor twenty-four generations back in time.21 This does not mean that Queen Elizabeth II did not inherit DNA from ancestors that far back, just that it is expected that only about 1,751 of her 16…

How should you address a cat?

Especially when that cat is your professor? I tend to err on the side of formality, mainly because I'm an old guy, and tend to be very informal. My professors all address me and the other students by their first names, which is fine by me, and a lot of the students reciprocate. So am I being polite or a hopeless fuddy duddy when I address emails to "Dear Professor X?"


The trouble with boys, say a couple of new studies, is that they have too much confidence. It seems that an average boy is likely to believe that he is smarter than average while average girls are less likely to. Lots of studies show that this effect is pervasive in women of all ages - at least above the age of 5. Moreover, confidence is known to play a big role in success, even though the Dunning-Kruger effect is in action (less competent persons are more likely to overestimate their competence than the more competent. Anyone who doubts these two principles should consider the case of our chief executive. So does this pervasive effect just reflect the ongoing success of the patriarchy in keeping the womenfolk down, or is there a biological basis? My guess would be a bit of both. Boys who lack confidence are urged to "grow a pair." Girls wind up growing pairs of organs that don't produce testosterone. The most demanding and prestigious jobs in society require co…

Genetic Similarity and Differences

Arun takes exception to the following in the Big South Asia genomics paper: While the earliest 450 group of samples (SPGT) is genetically very similar to the Indus_Periphery samples from the 451 sites of Gonur and Shahr-i-Sokhta, they also differ significantly in harboring Steppe_MLBA 452 ancestry (~22%).What does that "similar but different" mean, he asks. I have a couple of ideas (and I can't currently use his comment system), so here goes. All human DNA is highly similar. Numbers like 99.5% identical are often mentioned, so comparing similarities and differences depend on the relatively few sites (millions, actually, out of billions) where differences occur, in this case, the so-called Single Nucleotide Polymorphisms (SNPs) or single site on the genome where more than one of the four possible nucleotides is found, that is, places where Joe might have a Guanine or G, and Fred might have a Thymine, or T. Thus, detecting similarities to ancestral populations depends…

Whoa! I am old!

I was looking at my student file at the local U and noticed that it included my GRE scores, and when I had taken the exams: Jan 1, 1888. That seems a bit early.