Are Humans Adapted to Modern Life?
Gene selection may have slowed but we are evolving faster than ever before.
Posted September 17, 2015
Did gene-based evolution stop after the Agricultural Revolution? Is the Digital Age inhabited by Stone Age people as many evolutionary psychologists claim? I suggest that evolutionary processes — genetic and non-genetic — continue to this day.
Malthusian and Post-Malthusian
Evolution requires a struggle to survive: it cannot function unless the population is suppressed by a scarcity of food, or other resources. This is the Malthusian world view propounded by Thomas Malthus whose ideas deeply influenced Charles Darwin.
Economist Geoffrey Clark argues that fertility continued to be restricted by food availability right up to the Industrial Revolution from its onset around 1780 in England (1). This means that Darwinian evolution must have continued up to about two centuries ago.
Examples of human genetic evolution since the Agricultural Revolution include lactose tolerance in societies where milk was consumed by adults, and sickle cell anemia as a defense against malaria (2).
Following the Green Revolution (i. e., scientific agriculture) population was no longer restricted by food availability, so that the Malthusian era ended and Darwinian evolution stopped in its tracks.
The Industrial Revolution ushered in a post-Malthusian world where food supply no longer restricts the human population and where Darwinian evolution cannot work.
Ironically, as one surveys modern populations, the time since the Industrial Revolution is a period of remarkable biological diversity and much of this is predictably matched to the environment. People are taller than they have ever been before, for example, reflecting improved nutrition. We are also fatter than ever before, due mainly to our sedentary lifestyle as our prey shifted from the African savannah to computer screens.
Such changes generally do not help us to survive, or reproduce. Yet, at least some of the biological changes in people since the Industrial Revolution are functional. They do help us to succeed in modern environments. One of the more obvious is the rise in IQ scores with economic development, called the Flynn effect (3).
The Flynn effect is but one of many kinds of change wrought by the post-Malthusian environment. The Industrial Revolution is a grand enrichment experiment analogous to those conducted on lab rats who were given a variety of toys to play with resulting in superior capacity to learn complex mazes that is equivalent to an animal IQ test.
As I pointed out in an earlier post, brain researchers are finding that our brains are fundamentally altered by what we ask them to do. So taxi drivers in London who must memorize the entire layout of the streets manifest permanent alteration in the hippocampus (4). Similar phenomena are surfacing in the digital age as young people who grow up in the digital world develop skills for visual perception and movement that are quite unlike anything seen in earlier generations. One of the more obvious effects is extraordinarily rapid keystrokes.
Such changes in the modern human brain come from an evolved plasticity that we share with other mammals. They occur without alteration of gene frequencies but they resemble adaptations in the match between brain capacity and behavior.
Evolution without genes is real and was observed in various social animals (3). Diverse creatures from black rats, to kestrels, and chimpanzees master the problems of adaptation without any change in gene frequencies.
The Mauritius kestrel faced extinction because its nests, built in tree cavities, were vulnerable to monkeys that had been introduced to the island by humans (5). In 1974, one pair of kestrels nested on a cliff face that was safe from monkeys. The young prospered and bred at the same site because birds develop a preference for sites resembling those where they were raised. So cliff nesting evolved without any change in gene frequencies of the population.
Human Evolution Without Genes
Humans are masters of speeding up adaptation by non-genetic means, such as making fires and wearing clothes to survive cold winters. Early garments consisted largely of animal skins thereby appropriating the genetic adaptations of other species.
Economic development favors low fertility (and monogamous marriage) due to the huge costs and high parental investment required to raise children who can succeed today (3). Improving standards of living, and health, in developed countries mean that there is less fear of early and sudden death so that religion — that helps people deal with such existential fears — is in decline (6).
In summary, our bodies, our brains, and our psyches change in ways that help us to fit in with the post-Malthusian world. We are evolving to fit in with modern conditions, but that change is happening without any change in gene frequencies of the population.
1 Clark, G. (2007). A farewell to alms: A brief economic history of the world. Princeton, NJ: Princeton University Press.
2 Odling-Smee, J., Laland, K. N., & Feldman, M. W. (2003). Niche construction: The neglected process in evolution. Princeton, NJ: Princeton University Press.
3 Barber, N. (2015). Why behavior matches ecology: Adaptive variation as a novel approach. Cross-Cultural Research, 49, 57-89.
4 Maguire, E. A., Gadian, D. G., Johnsrude, I. S., Good. C. D., Ashburner, J. Frackowiac, R. S., and Frith, C. D. (2000). Navigation-related strutural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences, 97(8), 4398-4403. doi:10:1073/pnas.070039597.
5 Colias, N. E., & Colias, C. (1984). Nest building and bird behavior. Princeton, NJ: Princeton University Press.
6 Barber, N. (2012). Why atheism will replace religion: The triumph of earthly pleasures over pie in the sky. E-book: http://www.amazon.com/Atheism-Will-Replace-Religion-ebook/dp/B00886ZSJ6/