A pointillist view of human evolution and variation.

In a very abstract and stylistic way the first figure represents the genetic variation that had already accumulated in anatomically modern humans in Africa between 150,000 years BP and 100,000 years BP; that genetic variation is represented by the different colored dots. Notice that the colors are not evenly distributed across the continent as would be expected from an isolation by distance model. There is a bit more "red" in South Africa; there is a bit more "blue" and "yellow" in Northeast Africa.

 About 100,000 years BP some peoples from Northeast Africa migrated into Southwest Asia as shown in the second figure. Since the people who migrated origininated from the populations of Northeast Africa, they sampled from that already partially diverged gene pool and the sampling error accentuated the loss of variation. Only a fraction of the genetic variation in Africa as a whole was represented in that initial "non-African" population. It was that population in Southwest Asia that then increased in numbers and spread geographically to occupy all of Eurasia and Australo-Melanesia by about 40,000 years BP, as shown in the third figure. There was not enough time for much new genetic variation to arise but some of the variation in Southwest Asia that spread into Europe was lost by the populations that eventually reached far East Asia.

 Some time more recent than 40,000 years BP some of the populations from Siberia and the east coast of Asia migrated to the Americas and expanded to occupy both North and South America. Some additional variation was lost during that colonization but the effect was less than associated with the migration out of Africa.

 © 1999 Kenneth K Kidd, Yale University. All rights reserved. This material may be reproduced for classroom use only.