In this case, the question is interpreted as, is natural selection still operating on humans? BBC News discussed the question with a few scientists whose research speaks to the question. The report also discusses some areas of recent human “evolution,” such as changes in metabolism and the ability for adults to digest lactose. (But more on that in a moment.)
University College London geneticist Steve Jones tells the BBC,
“In Shakespeare’s time, only about one English baby in three made it to be 21. All those deaths were raw material for natural selection, many of those kids died because of the genes they carried. But now, about 99% of all the babies born make it to that age. Natural selection, if it hasn’t stopped, has at least slowed down.”
BBC News also spoke with Yale University evolutionary biologist Stephen Stearns, who argues that natural selection is still working because some people choose to have fewer children than others. A study of the medical history of Framingham, Massachusetts, showed that the inhabitants of Framingham “are still evolving,” in the report’s wording, with decreases in height and increases in weight over time. (Apparently overeating was ruled out as a factor.) Stearns’ interpretation of the study is that
“we are continuing to evolve, that biology is going to change with the culture and it’s just a matter of not being able to see it because we’re stuck right in the middle of the process right now.”
For example, the “evolution” of adult lactose tolerance is actually due to a mutation that fails to turn off our already-existing ability to digest lactose.
In other words, the rate of human evolution may increase, in spite of how technology protects us from environmental dangers, because the forces of globalization, culture, and the like influence reproductive rates. But as we often point out, this sort of “evolution” is quite different from the sort invoked to explain the origin of humans, with information-adding mutations over time. (For more, see our note at the end of this week’s item "#4".) For example, the “evolution” of adult lactose tolerance is actually due to a mutation that fails to turn off our already-existing ability to digest lactose. In this sense those of us who can digest lactose as adults are “degenerate mutants”!
In related news, scientists have determined that “smaller changes in multiple genes may have been the primary driver of changes in human phenotypes” rather than “a new, advantageous gene [that] appears and quickly spreads through the population.” While not direct evidence against “information adding” mutations, the research does align with our perspective that small “horizontal” genetic changes as well as degenerative changes, not information-adding changes, account for the majority of our biological diversity.
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