Topic of Article
The authors summarize the findings of genomic surveys to determine whether human genetic evolution is slowing or accelerating.
As this is a very technical article, I would not recommend reading it. I do think, however, that their findings are important to understand. Too many historical thinkers assume that human genetic evolution ended thousands of years ago, so they do not factor biology into their theories of why human societies changed.
- While most people believe that human genetic evolution has slowed down over the last 40,000 years, the data shows that it has speeded up.
- Increasing population size is a key driver in genetic evolution. This has clearly been true of humans.
- Changes in human population size suggest that our genetic evolution is now >100 times higher than characterized most of human evolution.
Important Quotes from Article
Genomic surveys in humans identify a large amount of recent positive selection. Using the 3.9-million HapMap SNP dataset, we found that selection has accelerated greatly during the last 40,000 years.
The past 10,000 years have seen rapid skeletal and dental evolution in human populations and the appearance of many new genetic responses to diets and disease.
In such a transient, large population, size increases the rate and effectiveness of adaptive responses.
Population growth itself predicts an acceleration effect, because the number of new mutations increases as a linear product of the number of individuals, and exponential growth increases the fixation probability of new adaptive mutations.
Population growth in the Upper Paleolithic and Late Middle Stone Age began by 50,000 years ago. Several archaeological indicators show long-term increases in population density, including more small-game exploitation, greater pressure on easily collected prey species like tortoises and shellfish, more intense hunting of dangerous prey species, and occupation of previously uninhabited islands and circumarctic regions. Demographic growth intensified during the Holocene, as domestication centers in the Near East, Egypt, and China underwent expansions commencing by 10,000 to 8,000 years ago. From these centers, population growth spread into Europe, North Africa, South Asia, Southeast Asia, and Australasia during the succeeding 6,000 years.
Sub-Saharan Africa has no archaeological evidence for agriculture before 4,000 years ago. West Asian agricultural plants like wheat did poorly in tropical sun and rainfall regimes, while animals faced a series of diseases that posed barriers to entry. As a consequence, some 2,500 years ago the population of sub-Saharan Africa was likely <7 million people, compared with European, West Asian, East Asian, and South Asian populations approaching or in excess of 30 million each. At that time, the sub-Saharan population grew at a high rate, with the dispersal of Bantu populations from West Africa and the spread of pastoralism and agriculture southward through East Africa.
It is sometimes claimed that the pace of human evolution should have slowed as cultural adaptation supplanted genetic adaptation. The high empirical number of recent adaptive variants would seem sufficient to refute this claim… Because of the recent acceleration, many more new adaptive mutations should exist than have yet been ascertained, occurring at a faster and faster rate during historic times…
To the extent that new adaptive alleles continued to reflect demographic growth, the Neolithic and later periods would have experienced a rate of adaptive evolution >100 times higher than characterized most of human evolution. Cultural changes have reduced mortality rates, but variance in reproduction has continued to fuel genetic change. In our view, the rapid cultural evolution during the Late Pleistocene created vastly more opportunities for further genetic change, not fewer, as new avenues emerged for communication, social interactions, and creativity.