Are Humans Adapted to Modern Environments?
Genes are not the only way of matching mammals with their environments.
Posted Apr 11, 2017
Our two main theories of human behavior do a poor job of explaining how humans change to meet the demands of varied environments. One theory -cultural determinism – mostly denies that this happens. The other – evolutionary psychology – claims we are matched to the environments of our remote ancestors.
Weaknesses of both theories are exposed by recent evidence that other species are better adapted to modern environments than previously suspected. As the species that colonizes new habitat unlike any other, humans are better adapted than most.
Other Vertebrates Are Adapted to Modern Conditions
The view of adaptation as a very slow process requiring hundreds of generations of gene selection is a commonplace in biology with the leg bones of horses gradually changing over tens of millions of years of living on grasslands, for instance (1).
So evolutionary psychologists assumed that behavioral evolution was extremely slow as well. So humans could not be psychologically, or behaviorally adapted to modern conditions.
Other vertebrates are actually very good at adjusting to altered environments through rapid behavioral change.
Until recently, it was widely assumed that human fears of snakes, spiders, and large predators such as lions were partly inherited by genetic means but they are likely affected by social learning.
Moreover, fear of predators by other prey species, such as moose, is entirely learned in the lifetime of the individual (2). Indeed, when leading predators, such as wolves and brown bears go extinct, moose lose all fear of their scent in a single generation. When wolves were reintroduced to their habitat, fear returned within a generation or two, probably due to social learning of the reactions of mothers in addition to individual experiences. If moose can get behaviorally adapted to their changing environment within a generation or two, the same is almost certainly true of humans who, after all, have a richer repertoire of social learning, including sophisticated tools.
Humans Are Better Adapted to Varied Modern Environments
Early humans were probably very good at exploiting varied resources. Anthropologists believe that Homo erectus had both butchered animals with stone choppers and used fire to cook meat for over a million years (3). Although they likely took advantage of naturally occurring bush fires, there was at least one population, at Gesher Benot Ya'Aqov in the north of Israel where hearths were regularly used from 750,000 years ago. This population was involved in hunting large game, catching fish, and cooperative movement of large stone slabs used in tool manufacture.
Our remote ancestors were quite skilled at striking slivers off cores with a hammer stone that served as primitive knives for butchering meat. Yet, archaeologists found little qualitative development in the kind of stone tools that early humans used over more than a million years (3). Approximately 100,000 years ago, finely crafted spears and arrows emerged amongst South African cave dwellers that allowed humans to kill prey animals from a distance. These weapons were so effective that humans wiped out most of the large grazing animals wherever they migrated, an event known as the Pleistocene overkill.
If this hypothesis is correct, it is likely that modern humans were so successful at extracting high energy foods that they were forced to migrate as their game resources became depleted.
This sketch of our archaeological past implies that our ancestors were very good at adjusting to new habitat, by exploiting new food sources, and surviving in a range of climatic extremes. This process of adaptation to new ecologies was mostly non genetic given that gene selection is too slow to accomplish most of the necessary changes.
Mechanisms of Adaptation Without Genetic Change
As our ancestors migrated out of Africa, they encountered much colder climates and likely adapted by using animal skins to keep themselves warm. In that way, they appropriated a biological adaptation that was the product of millions of years of genetic evolution and used it for much the same purpose in an immediate solution.
For satisfactory clothing, hides had to be properly cured and deftly stitched. The crucial task of clothes making in cold-adapted populations like the Inuit is performed mostly by women, representing a time-honored division of labor and superior manual dexterity.
Of course, there is a body of inherited knowledge underlying such skills – knowledge that is unlikely to be lost given that it is critical for survival.
Knowledge and skills may be lost over time. One well-known example is the loss of boat-building technology by aboriginal residents of Tasmania (4). Anthropologists now believe that when the island lost its land bridge to the mainland that the remaining population was too small to sustain specialized boat-building skills.
Clearly, technological innovations helped humans to solve problems easily and quickly that defeated other mammals and primates. These solutions had to be produced quickly as our ancestors migrated to new habitats so that gene selection was mostly irrelevant.
The evidence indicates that we became only too successful everywhere we migrated, wiping out large game animals in the Pleistocene overkill. So even if there was no time for gene selection, our hunting forbears were highly adapted to new ways of life contrary to the views of cultural determinists.
1. Ruse, M. (1982). Darwinism defended: A guide to the evolution controversies. London: Addison-Wesley.
2. Berger, J., Swenson, J. E., & Persson, I. L. (2001). Recolonizing carnivores and naïve prey: Conservation lessons from Pleistocene extinctions. Science, 291, 1036-1039.
3. 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.
4. Henrich, J. (2004). Demography and cultural evolution, why adaptive cultural processes produced maladaptive losses in Tasmania. American Antiquity, 69, 197-214.