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The Journey of Man

Spencer Wells "The Journey of Man: A Genetic Odyssey" explores the role of genetics in tracing the history of human expansion across the world. The primary means of accessing this spread is various markers on the Y-chromosome. Since these markers don't change except through rare mutations, by looking at the concentration of specific markers throughout the world it is possible to trace the human population back to a genetic Adam. There is an equivalent genetic Eve, but the data isn't as good. This is later attributed to the paternal nature of most human societies, in that the woman traveled to the man's village thus causing more dispersion of genes.

Overall I enjoyed the book and feel that the author presented a very compelling case that humans did originate in Africa and then spread out across the rest of the world at various points through time. More importantly, that spread occurred in a very short amount of time, compared to the age of the earth.

Some interesting notes I captured while reading:

Herbert Spencer actually coined the phrase 'survival of the fittest'. [11]
People previously used the genetic differences to claim superiority, which manifested as the Eugenics movement. [11]
The majority of genetic differences are found within the same population, up to 85%. [17]
Ockham's razor (parsimony) is used frequently when looking at genetic history and the migration of humans. [22]
Genetic diversity first started 200,000 years ago. [32]
Homo erectus didn't evolve into Homo sapiens. While they did share common traits, they diverged a long time ago and Homo erectus eventually died out. [38]
The creation of the Sarah desert caused a forced migration and isolation that helped create certain branches of the genetic tree. [108]
Humans started leaving Africa about 50,000 years ago. [125]
Having grandmothers helps family since they take care of children while more able bodied adults do other tasks. [132]
About 15,000 years ago the first humans entered America via Siberia. They would become what are known today as Native Americans. [140]
Between the invention of agriculture (about 10,000 years ago) and 1750 the human population grew from 10 million to 500 million. [151]
Hindu castes show clear evidence of this pattern, with much greater Y-chromosome than mtDNA divergence between castes, suggesting that women could move between castes while men were locked into theirs. [176-177]

If you happen to get the book, page 182 has a wonderful world map that show the Y-chromosome genes that spread out over the world and the approximate years each branch was created.