6-4 How do evolutionary psychologists use natural selection to explain behavior tendencies?

Behavior geneticists explore the genetic and environmental roots of human differences. Evolutionary psychologists instead focus mostly on what makes us so much alike as humans. They use Charles Darwin’s principle of natural selection to understand the roots of behavior and mental processes. The idea, simplified, is this:

A fox is a wild and wary animal. If you capture a fox and try to befriend it, be careful. Stick your hand in the cage and, if the timid fox cannot flee, it may snack on your fingers. Russian scientist Dmitry Belyaev wondered how our human ancestors had domesticated dogs from their equally wild wolf forebears. Might he, within a comparatively short stretch of time, accomplish a similar feat by transforming the fearful fox into a friendly fox?

To find out, Belyaev set to work with 30 male and 100 female foxes. From their offspring he selected and mated the tamest 5 percent of males and 20 percent of females. (He measured tameness by the foxes’ responses to attempts to feed, handle, and stroke them.) Over more than 30 generations of foxes, Belyaev and his successor, Lyudmila Trut, repeated that simple procedure. Forty years and 45,000 foxes later, they had a new breed of foxes that, in Trut’s (1999) words, were “docile, eager to please, and unmistakably domesticated. . . . Before our eyes, ‘the Beast’ has turned into ‘beauty,’ as the aggressive behavior of our herd’s wild [ancestors] entirely disappeared.” So friendly and eager for human contact were these animals, so inclined to whimper to attract attention and to lick people like affectionate dogs, that the cash-strapped institute seized on a way to raise funds—marketing its foxes as house pets.

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Over time, traits that give an individual or species a reproductive advantage are selected and will prevail. Animal-breeding experiments manipulate genetic selection. Dog breeders have given us sheepdogs that herd, retrievers that retrieve, trackers that track, and pointers that point (Plomin et al., 1997). Psychologists, too, have bred animals to be serene or reactive, quick learners or slow ones.

Does the same process work with naturally occurring selection? Does natural selection explain our human tendencies? Nature has indeed selected advantageous variations from the new gene combinations produced at each human conception plus the mutations (random errors in gene replication) that sometimes result. But the tight genetic leash that predisposes a dog’s retrieving, a cat’s pouncing, or a bird’s nesting is looser on humans. The genes selected during our ancestral history provide more than a long leash; they give us a great capacity to learn and therefore to adapt to life in varied environments, from the tundra to the jungle. Genes and experience together wire the brain. Our adaptive flexibility in responding to different environments contributes to our fitness—our ability to survive and reproduce.

Our behavioral and biological similarities arise from our shared human genome, our common genetic profile. How did we develop our genetic kinship?

OUR GENETIC LEGACY At the dawn of human history, our ancestors faced certain questions: Who is my ally, who is my foe? With whom should I mate? What food should I eat? Some individuals answered those questions more successfully than others. For example, women who experienced nausea in the critical first three months of pregnancy were genetically predisposed to avoid certain bitter, strongly flavored, and novel foods. Avoiding such foods has survival value, since they are the very foods most often toxic to prenatal development (Profet, 1992; Schmitt & Pilcher, 2004). Early humans disposed to eat nourishing rather than poisonous foods survived to contribute their genes to later generations. Those who deemed leopards “nice to pet” often did not.

Similarly successful were those whose mating helped them produce and nurture offspring. Over generations, the genes of individuals not so disposed tended to be lost from the human gene pool. As success-enhancing genes continued to be selected, behavioral tendencies and thinking and learning capacities emerged that prepared our Stone Age ancestors to survive, reproduce, and send their genes into the future, and into you.

As inheritors of this prehistoric legacy, we are genetically predisposed to behave in ways that promoted our ancestors’ surviving and reproducing. But in some ways, we are biologically prepared for a world that no longer exists. We face problems our ancestors could not imagine, such as how to create the perfect online dating profile or how to overcome the urge to constantly check our smart phones (Parkinson & Wheatley, 2015). We love the taste of sweets and fats, nutrients that prepared our physically active ancestors to survive food shortages. But few of us now hunt and gather our food. Too often, we search for sweets and fats in fast-food outlets and vending machines. Our natural dispositions, rooted deep in history, are mismatched with today’s junk-food and often inactive lifestyle.

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EVOLUTIONARY PSYCHOLOGY TODAY Darwin’s theory of evolution has become one of biology’s organizing principles. “Virtually no contemporary scientists believe that Darwin was basically wrong,” noted Jared Diamond (2001). Today, Darwin’s theory lives on in the second Darwinian revolution, the application of evolutionary principles to psychology. In concluding On the Origin of Species, Darwin (1859, p. 346) anticipated this, foreseeing “open fields for far more important researches. Psychology will be based on a new foundation.”

Elsewhere in this text, we address questions that intrigue evolutionary psychologists: Why do infants start to fear strangers about the time they become mobile? Why are biological fathers so much less likely than unrelated boyfriends to abuse and murder the children with whom they share a home? Why do so many more people have phobias about spiders, snakes, and heights than about more dangerous threats, such as guns and electricity? And why do we fear air travel so much more than driving?

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We know from our correspondence and from surveys that some readers are troubled by the naturalism and evolutionism of contemporary science. (A note to readers from other nations: In the United States there is a wide gulf between scientific and lay thinking about evolution.) “The idea that human minds are the product of evolution is . . . unassailable fact,” declared a 2007 editorial in Nature, a leading science journal. In The Language of God, Human Genome Project director Francis Collins (2006, pp. 141, 146), a self-described evangelical Christian, compiled the “utterly compelling” evidence that led him to conclude that Darwin’s big idea is “unquestionably correct.” Yet Gallup pollsters report that 42 percent of U.S. adults believe that humans were created “pretty much in their present form” within the last 10,000 years (Newport, 2014). Many people who dispute the scientific story worry that a science of behavior (and evolutionary science in particular) will destroy our sense of the beauty, mystery, and spiritual significance of the human creature. For those concerned, we offer some reassuring thoughts.

When Isaac Newton explained the rainbow in terms of light of differing wavelengths, the British poet John Keats feared that Newton had destroyed the rainbow’s mysterious beauty. Yet, as evolutionary biologist Richard Dawkins (1998) noted in Unweaving the Rainbow, Newton’s analysis led to an even deeper mystery—Einstein’s theory of special relativity. Nothing about Newton’s optics need diminish our appreciation for the dramatic elegance of a rainbow arching across a brightening sky.

When Galileo assembled evidence that Earth revolved around the Sun, not vice versa, he did not offer irrefutable proof for his theory. Rather, he offered a coherent explanation for a variety of observations, such as the changing shadows cast by the Moon’s mountains. His explanation eventually won the day because it described and explained things in a way that made sense, that hung together. Darwin’s theory of evolution likewise is a coherent view of natural history. It offers an organizing principle that unifies various observations.

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Many people of faith find the scientific idea of human origins congenial with their spirituality. In the fifth century, St. Augustine (quoted by Wilford, 1999) wrote, “The universe was brought into being in a less than fully formed state, but was gifted with the capacity to transform itself from unformed matter into a truly marvelous array of structures and life forms.” Some 1600 years later, Pope Francis in 2014 welcomed a science-religion dialogue, saying, “Evolution in nature is not inconsistent with the notion of creation, because evolution requires the creation of beings that evolve.”

Meanwhile, many people of science are awestruck at the emerging understanding of the universe and the human creature. It boggles the mind—the entire universe popping out of a point some 14 billion years ago, and instantly inflating to cosmological size. Had the energy of this Big Bang been the tiniest bit less, the universe would have collapsed back on itself. Had it been the tiniest bit more, the result would have been a soup too thin to support life. Astronomer Sir Martin Rees has described Just Six Numbers (1999), any one of which, if changed ever so slightly, would produce a cosmos in which life could not exist. Had gravity been a tad stronger or weaker, or had the weight of a carbon proton been a wee bit different, our universe just wouldn’t have worked.

What caused this almost-too-good-to-be-true, finely tuned universe? Why is there something rather than nothing? How did it come to be, in the words of Harvard-Smithsonian astrophysicist Owen Gingerich (1999), “so extraordinarily right, that it seemed the universe had been expressly designed to produce intelligent, sentient beings”? On such matters, a humble, awed, scientific silence is appropriate, suggested philosopher Ludwig Wittgenstein: “Whereof one cannot speak, thereof one must be silent” (1922, p. 189).

Rather than fearing science, we can welcome its enlarging our understanding and awakening our sense of awe. In The Fragile Species, Lewis Thomas (1992) described his utter amazement that Earth in time gave rise to bacteria and eventually to Bach’s Mass in B Minor. In a short 4 billion years, life on Earth has come from nothing to structures as complex as a 6-billion-unit strand of DNA and the incomprehensible intricacy of the human brain. Atoms no different from those in a rock somehow formed dynamic entities that produce extraordinary, self-replicating, information-processing systems—us (Davies, 2007). Although we appear to have been created from dust, over eons of time, the end result is a priceless creature, one rich with potential beyond our imagining.