PRIMAL FEAR: Many animals show lasting changes in behavior and physiology after a traumatic experience
PTSD has deep evolutionary roots, and that some of its symptoms arise from adaptations, like a heightened state of alert, that allow individuals of many species, including our own, to manage danger.
SHARON LEVY: Behavioral ecologists Liana Zanette and Michael Clinchy,… both at the University of Western Ontario,… study what they call the ecology of fear, which combines the psychology of trauma with the behavioral ecology of fear in wild animals. They’ve found that fear of predators can cause other wild mammals and songbirds to bear and raise fewer young. The offspring of frightened voles and song sparrows, like those of stressed snowshoe hares, are less likely to survive to adulthood and succeed in reproducing.
These findings add to a growing body of evidence showing that fearful experiences can have long-lasting effects on wildlife and suggesting that post-traumatic stress disorder, with its intrusive flashback memories, hyper-vigilance and anxiety, is part of an ancient, evolved response to danger. The work is part of a wider scientific debate over the nature of PTSD and whether it is an evolved response shared among mammals, birds and other creatures, or is unique to humans…
Studies of the ecology of fear started in the 1990s. Before then, scientists assumed that the impact of a predator on an individual prey animal was either deadly or fleeting. If a hare survived a coyote attack, or a zebra escaped the claws of a lion, it would move on and live its life as before. But research shows that fear can alter the long-term behavior and physiology of wild animals, from fish to elephants, Zanette and Clinchy write in the 2020 Annual Review of Ecology, Evolution, and Systematics. “Fear is a response all animals mount to avoid being killed by predators,” says Zanette. “It’s enormously beneficial, because it keeps you alive to breed another day. But it does carry costs.”
The reasons to fear are clear. Recent studies have found that up to 32 percent of adult female giraffes in the Serengeti carry scars from lion attacks, 25 percent of harbor porpoises in the southern North Sea have claw and bite marks from gray seals and 100 percent of manta rays in some African waters bear multiple bite wounds from sharks. These survivors may carry memories of terror along with their physical scars…
Rudy Boonstra, a population ecologist at the University of Toronto, has studied the impacts of extreme stress on the snowshoe hares and other small mammals of the Canadian Yukon since the 1970s… Early pioneers of stress physiology focused on human problems and viewed such stress responses as pathological, but Boonstra has come to disagree. He sees the response of snowshoe hares as an adaptation that allows the animals to make the best of a bad situation. Animals stressed by many predators spend more time hiding and less time feeding, so they produce fewer young — but that may allow more adult hares to survive to rebuild the population when the cycle starts again…
Some of the most dramatic impacts of wildlife trauma have been observed in African elephants. Their populations have declined drastically due to poaching, legal culling and habitat loss. Undisturbed elephants live in extended family groups ruled by matriarchs, with males departing when they reach puberty. Today, many surviving elephants have witnessed their mothers and aunts slaughtered before their eyes. A combination of early trauma and the lack of stable families that would ordinarily be anchored by elder elephants has resulted in orphaned elephants running amok as they grow into adolescence.
“There are interesting parallels between what we see in humans and elephants,” says Graeme Shannon, a behavioral ecologist at Bangor University in Wales who studies the African elephant. Trauma in childhood and the lack of a stable family are major risk factors for PTSD in people. And among elephants who’ve experienced trauma, Shannon notes, “we’re seeing a radical change in their development and their behavior as they mature.” Elephants can remain on high alert years after a terrifying experience, he says, and react with heightened aggression…
Brain imaging studies have shown that people with PTSD have less volume in their hippocampus, a sign that neurogenesis — the growth of new neurons — is impaired… This is why people with PTSD are haunted by vivid memories of an ordeal long after they’ve reached safety. In a similar manner, fear of predators suppresses neurogenesis in lab rats. And Zanette and Clinchy are demonstrating that the same pattern holds in wild creatures living in their native habitats… The same pattern has been shown in wild mice and in fish living with high levels of predator threat. These neurochemical signals parallel those seen in rodent models of PTSD that researchers have long used to understand the syndrome in humans…
Despite the mounting evidence that a wide range of animals experience long-term impacts of extreme stress, many psychologists still see PTSD as a uniquely human problem… Some researchers now disagree with this human-centric view of PTSD, however. “A lot of things are shared between humans and other mammals,” says Sarah Mathew, an evolutionary anthropologist at Arizona State University. This includes learning about and responding to danger, and avoiding situations that present life-threatening risks. Mathew believes that PTSD has deep evolutionary roots, and that some of its symptoms arise from adaptations — like a heightened state of alert — that allow individuals of many species, including our own, to manage danger. SOURCE…
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