Evidence that psychology, like biology, is conserved between human and nonhuman species augurs a shake-up for science and society
G. A. Bradshaw, Robert M. Sapolsky
Back in 1974, an unusual report from Jane Goodall at the Gombe Stream Wildlife Research Centre in Tanzania caught the public eye. Chimpanzees had committed infanticide and were engaging in war. Not only were they acting in unanticipated ways, chimpanzees were acting like humans. Goodall's discovery bridged the divide between Homo sapiens and other species.
In and of itself, similarity between species is no surprise. Scientists have long experimented on animals in place of people; the resulting insights form the backbone of biomedicine and anthropology. We accept that human beings and nonhuman animals share a common ancestry. In biology and psychology, this relationship is the scientific rationale for a system of inference—the process and convention used to draw logical conclusions from observations—that allows humans to benefit from research with animal subjects. As such, it was not Goodall's discovery of species similarity per se that provoked such curiosity; it was the specific nature of the similarity.
Naked Ape, Hairy Human
The Gombe observations blurred the boundary between animal and human behavior, between nature and human nature. Previously, behaviorists thought that human and animal psychology intersected only in the realm of instinct. Homicide—as opposed to killing for access to territory or a mate—was deliberate, not instinctive. Infanticide and murder were considered exclusive to human beings and outside of nature. Goodall's findings challenged this received wisdom.
Since then, what we know about ourselves and other species has changed substantially. Many studies have documented in other species the same behaviors that enrich human lives. We now recognize that species other than humans engage in an array of behaviors that bring variety and depth to life: dolphins teach cultural customs to their young, octopi demonstrate diverse personalities, and rats show a sense of humor. Once at odds with the conventions of her discipline, Goodall's interpretations today are supported by decades of research in neurobiology. They are part of a broad conceptual framework that has coalesced around the idea that psychology, like biology, is conserved among animals.
This idea isn't new. Charles Darwin placed human beings on the continuum of animal species nearly 150 years ago. Somehow that insight was lost. Nurture is being reconciled with nature, and boundaries that once separated academic disciplines are dissolving, all of which bring models of animal and human behavior to unity. Separation has given over to integration, and what seemed like a haphazard collection of observational anomalies is now taking form as a coherent, human-inclusive, trans-species theory of mind and body.
In addition to and underlying these changes in theory, Goodall's data contradicted inferential conventions. Chimpanzee violence suggested that ethologists could infer the origins of chimp behavior from what they understood about human violence—something hitherto dismissed as being contrary to scientific standards.
Historically, science has admitted inference from animals to humans but not the reverse. As historians Lorraine Daston of the Max Planck Institute for the History of Science in Berlin and Gregg Mitman of the University of Wisconsin–Madison, recently noted,
Ethologists who study animal behavior, including that of primates, with close phylogenetic links to humans, have long made it a principle not to infer humanlike mental states from humanlike behavior and until [recently] many scientists in the field frowned upon any discussion of animal mental states.
Perhaps because scientists have been trained to shun such conclusions, examples of human-to-animal inference have been scarce in the scientific literature. This is one of the reasons that chimpanzee homicide, laughing mice and empathetic sheep are considered newsworthy: They represent deviations from normative models—or rather they used to. Now erstwhile behavioral isolates make up the empirical bricks in the foundations of psychobiology, and the limits on what we can infer about humans and animals have changed. Human-to-animal and animal-to-human inferences are legitimately symmetric. A deeper understanding of brain biology has strengthened this sense of equity.
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