Montag, 12. Februar 2007

Human traits and their evolution - a new book

The OMIM-databank ("Online Mendelian Inheritance in Man") is full of scientific literature concerning data and theories about the evolutionary causes of the worldwide distribution (frequencies) of inborn human traits - of EVERY inborn human trait, we know about today. Only very few popular science books exist today, that try to give the public an understanding at least of the tip of the iceberg, that is formed by that databank - that is humanity's knowledge about itself. So a lot of reason exist to welcome books, that are publicised in that field. We have to thank "Gene Expression" once more for giving a hint to a new book in this field:

A review of Survival of the Sickest, by Sharon Moalem with Jonathan Prince


Most of the chapters are centered around the population genetics of a disease. This is fascinating material, and Moalem (along with his co-author) does a wonderful job presenting it. Each chapter starts with an observation--a high prevalance of Type I diabetes in Europeans, the frequency of a genetic disease called hemochromatosis, or the geographic distribution of favism, for example--which sets the stage for a series of anecdotes that eventually leads the reader to his evolutionary hypothesis (for the examples given, these hypotheses are adaptation to cold and resistance to the plague and malaria, repectively). Some of these anecdotes are worth the price of the book alone (though, it must be noted, I didn't pay for my copy, so I suppose I can't judge)--there's an investigation of the biology of a toad that allows itself to freeze solid each winter that is particularly remarkable, and the section on host manipulation by parasites would make Carl Zimmer proud. A large number of human traits are touched on from this perspective--apart from the ones mentioned above, traits like skin color, alcoholism, taste, and even skull shape get mentions[1].

While these chapters are the highlight of the book, an alert reader may notice a couple hints that perhaps the science isn't definitive on some of these stories: first, the oft-added qualifier that a given theory (for example, that the high rate of hypertension in African-Americans is due to selection for salt retention on slave boats) is "controversial", and second, that there are a number of theories for some of the observations. The prevalence of diabetes, for instance, is attributed to metabolic systems unaccustomed to carbohydrate-rich diets (pg. 26), a selective sweep for better cold response during the Younger Dryas (pg. 46), and transgenerational epigentic effects, the so-called "thrifty phenotype" hypothesis (pg. 166). These possibilities are not mutually exclusive, but a reconciliation of all of them would certainly have been desirable.


[1] Moalem gives a cursory look at the concept of "race" with regard to these traits, but essentially chooses not to discuss it, preferring to cite a Nature Genetics editorial from 2001 as saying that "population clusters identified by genotype analysis seem to more informative than those identified by skin color or self-declaration of race". Regular readers know that much has changed since 2001; in particular, there doesn't seem to be much of a distinction between genetic clusters and clusters based on self-declaration of race [Tang et al. 2005].

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