The Journey of Man: A Genetic Odyssey Read Online Free PDF

American named Bryant and an Englishman named Mourant, building on the work of the Hirszfelds, began to test blood samples from around the world. Over the next thirty years these twomen and their colleagues would examine thousands of people, from hundreds of populations, both living and dead. Bryant and his wife (like the Hirszfelds, another of the marital duos in population genetics) even went so far as to test American and Egyptian mummies, establishing the ancient nature of the ABO polymorphisms. In 1954 Mourant drew together the rapidly expanding body of blood group data in the first comprehensive summary of human biochemical diversity,
The Distribution of the Human Blood Groups
– a seminal work that became the standard text of experimental human population genetics for the next twenty years. This was the beginning of the modern era of human genetics.
    While the Hirszfelds clearly felt that their data on blood groups supported a racial classification that had become blurred by recent migration, and Carleton Coon later used them to support his theories of discrete subspecies, no one had actually tested the genetic data to see if there was any real indication of racial subdivision. This obvious analysis was finally carried out in 1972 by a geneticist whose primary research interest, oddly enough, was fruit flies – not humans.
    Using the data collected by Mourant and others, Richard Lewontin, then a professor at the University of Chicago, performed a seemingly trivial study of how human genetic variation sorted into within- versus between-group components. The question he was tying to answer, objectively, was whether there was any indication in the genetic data of a distinct subdivision between human races. In other words, he was directly testing the hypotheses of Linnaeus and Coon about human subspecies. If human races showed significant differences in their patterns of genetic diversity, then Linnaeus and Coon must be right.
    Lewontin describes the development of the analysis:
    The paper was written in response to a request … to contribute an article to the new journal
Evolutionary Biology
. I had been thinking at that time about diversity measures … not in the context of population genetics, but in the context of ecology. I had to take a very long bus trip to Bloomington, Indiana, and I had long had the habit, when going on trains and buses, of writing papers. I needed to write this paper, so I went on the bus trip with a copy of Mourant and a table of p
ln
p [a mathematical table used for calculating the diversity measure].On this bus trip, he began what would become one of the landmark studies in human genetics. In the analysis, Lewontin used as his model the new science of biogeography (the study of animal and plant geographic distributions) because he thought this was analogous to what he was doing with humans – looking for geographic subdivisions in order to define race. In fact, unsure of how to define a ‘race’ objectively, he divided humans largely along geographical lines – Caucasians (western Eurasia), Black Africans (sub-Saharan Africa), Mongoloids (east Asia), South Asian Aborigines (southern India), Amerinds (Americas), Oceanians and Australian Aborigines.
    The surprising result he obtained was that the majority of the genetic differences in humans were found within populations – around 85 per cent of the total. A further 7 per cent served to differentiate populations within a ‘race’, such as the Greeks from the Swedes. Only 8 per cent were found to differentiate between human races. A startling conclusion – and clear evidence that the subspecies classification should be scrapped. Lewontin says of the result:
    I had no expectation – I honestly didn’t. If I had any prejudice, it probably was that the between-race difference would have been a lot larger. This was reinforced by the fact that, when my wife and I were in Luxor [Egypt], years before it was overrun with tourists, she