Tag: Archaeogenetics

European man, Y chromosomes & tea leaves

By Razib Khan | September 3, 2010 4:00 am

Sydney_opera_house_side_viewSometimes in applied fields artistic license is constrained by the necessity of function to particular creative channels. Architecture comes to mind, at least before innovative technologies produced lighter and stronger materials, freeing up form from its straitjacket (whether this was a positive development is a matter of taste). But there’s only so much you can do with your palette when your palette is limited. This can be a bug, or it can be a feature. Science is not art, but in some ways at its heart it’s a story about the universe. The story can be in words or math, no matter, ultimately it’s the human attempt to map nature and make its subtle patterns comprehensible to us in plainer fashion. Some of the human biases in our quest are transparent. Why is there anthropology? A whole discipline devoted to the study of mankind and his nearest biological kin. We don’t peruse the patters with an objective and uninterested eye. We’re shaped by our presuppositions, as well as the constraints of the methods, and the results we have before us. The emergence of a theoretical evolutionary biology in the decades before the molecular revolution after World War II may have been in part simply a function of the fact that there were only so many results one could squeeze out of classical evolutionary genetic techniques, which relied on tracking only a limited set of phenotypes due to large effect mutations in breeding populations. With the rise of molecular evolution you saw the crystallization of theoretical frameworks, such as the neutral theory, to explain the burst of novel results.

ResearchBlogging.orgAround the year 2000 something similar happened in historical population genetics. The analysis of mtDNA lineages, passed from mother to daughter, had matured, and techniques for typing the Y chromosome had started to catch up, so that a symmetry between the sexes could arise. “Mitochondrial Eve” was now paired with “Y chromosomal Adam.” Though mtDNA and Y lineages were only two direct lines of ancestry, because there was no recombination across much of their sequence it was easy to analyze them within the context of coalescent theory. In contrast, the genealogy of autosomal regions of the genome were confounded by recombination, which mixed & matched the variation in a manner which made reconstruction of past history far more difficult. So we had the technology to extract the genetic variation from mtDNA and the Y chromosome, and, we knew how to model their evolution. The two together produced a genetic time machine.

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CATEGORIZED UNDER: Genetics, History

The science of human history as written by Herodotus

By Razib Khan | March 28, 2010 2:15 am

The following passage is from the epilogue of The Real Eve: Modern Man’s Journey Out of Africa by Stephen Oppenheimer:

In this book I have offered a synthesis of genetic and other evidence. Everything points to a single southern exodus from Eritrea to the Yemen, and to all the non-African male and female gene lines having arisen from their respective single out-of-Africa founder lines in South Asian (or at least near the southern exit). I regard the genetic logic for this synthesis as a solid foundation, and I have based the rest of my reconstruction of the human diaspora upon it. Obviously, the ‘choice’ of starting point (mine or theirs) determined all the subsequent routes our ancestors and cousins took. Tracing the onward trails is only possible as a result of marked specificity in regional distribution of the genetic branches The geographic clarity of both male and female gene trees is a big departure from the fuzzy inter-regional picture shown by older genetic studies. The degree of segregation of lines into different countries and continents is in itself good evidence that once they got to their chosen new homes, the pioneers generally stayed put, at least until the Last Glacial maximum forced some of them to move. This conservative aspect of our genetic prehistory also provides a partial explanation for the fact that when we look at a person, we can usually tell, to the continent, where their immediate ancestors came from, and underlies differences that some of us still call ‘race.’

Oppenheimer wrote the above in the early aughts, as his book was published in 2003. Much of this is generally in line with the ‘orthodoxy’ of the day. I believe that Oppenheimer’s assertion that there was one southern migration out of Africa by anatomically modern humans has gained some advantage over the alternative model of two routes, northern and southern, over the past ten years (Spencer Wells’ The Journey of Man sketches out the two wave model). Other assertions and assumptions have not stood the test of time. In particular, I would contend that generally the ‘conservative aspect of our genetic prehistory’ can no longer be taken for granted. Specifically, it seems likely now that much occurred after the Ice Age and during the Neolithic.

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Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!
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