Are Humans Still Evolving?
Evolution involves a lot more than gene selection.
Posted June 21, 2018
On remote islands, evolutionary change occurs at unusual speed, crafting migrant species into unique locally-adapted species. Humans prosper everywhere unlimited by island barriers. Are we still evolving?
What Island Populations Reveal
Charles Darwin witnessed the evolutionary-laboratory aspect of islands in the Galapagos where he observed giant tortoises, marine iguanas, and other species found nowhere else. He realized that these unique animals were forged in the volcanic crucible of that place, contradicting widely held single-creation views of the time.
Perhaps the most remarkable island from an evolutionary perspective is Madagascar, lying hundreds of miles east of the African mainland. Approximately 90 percent of the animal species there are unique to the island.
Just as Australia has diverse marsupials found nowhere else, Madagascar has a wide range of lemurs documented in Richard Attenboro's film (Madagascar, 2011). These range from large monkey-like sifakas to tiny mouse-like reed lemurs that survive only in the reed beds of a single lake.
The common pattern involves the emergence of new evolutionary specialization of form, appearance, physiology and behavior.
Behavioral Adaptations and Genetic Determinism
Darwin did not know exactly how such evolutionary change worked but guessed that some inherited traits gave individuals an advantage in the competition to survive and reproduce and that these were accentuated over time.
Modern biology integrated Darwin's theory with genetics and population biology, creating an emphasis on genes as the selective mechanism underlying evolutionary change. It is becoming clear that evolution works by other mechanisms, including learning, that are particularly important for humans.
There are other serious problems with genetic determinism.
One difficulty is that seemingly heavily genetic traits, such as extroversion, are not affected to any substantial degree by specific genes in the human genome that is now mapped (1).
Another problem is that in modern societies there is little infant, child, or young-adult mortality. This means that natural selection cannot favor one genotype over another particularly in modern environments where most people have very small families.
Has natural selection stopped working on our species? Or does evolutionary change continue to occur with gene selection pushed into the background in favor of behavioral adaptation?
Adaptation to Modern Life
Modern humans adapted very quickly to tool use with the emergence of fine motor skills, brain lateralization, and so forth (2). A refined diet also changed the anatomy of teeth, and jaws, and reduced gut size permitting increased brain volume.
Rapid genetic evolution continued, even after the Agricultural Revolution that brought diverse regional variation in lactose tolerance, alcohol tolerance, skin color, and malarial resistance depending upon the type of agriculture practiced (3).
In the modern world, however, there is less of a struggle for existence. This means that gene selection stopped in its tracks (although the genotype of an individual is altered by experience in the sense that some genes are silenced, 4). Examples include effects of stress on height and IQ.
Despite the stopping of conventional Darwinian evolution, humans continue to adapt to environmental change at a torrid pace. For example, learning to read changes the functioning of the brain and the complexity of modern life boosts intelligence. Moreover, we became much less physically violent as competition shifted from individual face offs to a contest over wealth and status (5).
There is no scientific justification for considering modern humans separate, or distinct, from other evolved creatures on this fragile and ever-changing planet.
Like other species, we continue to be modified by changing ecological conditions. Evolution never really stopped for us. We are very different from our ancestors of a mere one-tenth of a million years ago.
Far from stopping, the pace of change quickened over the past 10,000 years.
The only difference is that evolution shifted from gene selection to other forms of adaptation including learning and flexible child development. The same mechanisms of adaptation apply to other species.
1 Lukaszewski, A. W., and von Rueden, C. (2015). The extroversion continuum in evolutionary perspective. Personality and Individual Differences, 77, 186-192.
2 Henrich, J. (2015). The secret of our success: How culture is driving human evolution domesticating our species and making us smarter. Princeton, NJ: Princeton university Press.
3 Cavalli-Sforza, L. L., Menozzi, P., & Piazza, A. (1996). The history and geography of human genes. Princeton, NJ: Princeton University Press.
4 Moore, D. S., (2015). The developing genome: An introduction to behavioral epigenetics. New York: Oxford University Press.
5 Ridley, M. (2010). The rational optimist. New York: Harper Collins.