African elephants that have lived through the trauma of a cull—or selected killing of their kin—may look normal enough to the casual observer, but socially they are a mess. That’s the conclusion of a new study, the first to show that human activities can disrupt the social skills of large-brained mammals that live in complex societies for decades. The finding, experts say, has implications for conservation management, which often solely focuses on the number of animals in a population, and may extend to chimpanzees, dolphins, whales, and other species.

“It is a groundbreaking study, because it is the first to demonstrate, experimentally, a direct connection between the effects of culling and specific psychosocial harms,” says Lori Marino, a neuroscientist and expert on dolphin behavior at Emory University in Atlanta, who was not involved with the research. “It shows unequivocally that elephants are psychologically damaged by culling.”

Wildlife officials often used culling as a conservation tool in South Africa from the 1960s to the 1990s. (It is still reserved as a management tool there.) At the time, wildlife managers worried that if there were too many elephants in a fenced reserve, like the famed Kruger National Park, the behemoths would ultimately destroy the habitat, eating or trampling all the vegetation and uprooting the trees. During a cull, a helicopter pilot herds an elephant family into a tight bunch. Professional hunters on the ground then shoot the animals as quickly as possible. Only young elephants ranging from about 4 to 10 years old are saved. Park officials typically shipped them to other parks that lacked elephants or had smaller populations to increase the herds, because elephants are popular with tourists.

“Some of these elephants ended up in Pilanesberg National Park,” in South Africa’s North West Province where part of the new study was carried out, says Graeme Shannon, a behavioral ecologist at Colorado State University, Fort Collins, and the lead author of the new study. “Twenty to 30 years have passed since the actual cull and relocation.”

Scientists have known since the late 1990s that many of these elephants were psychologically affected by their experiences during the culling. Other studies have described these effects as akin to posttraumatic stress disorder. For instance, the orphaned male elephants at Pilanesberg and another reserve made headlines for attacking and killing 107 rhinoceroses over a 10-year period, something that elephants had never been reported to do. Other researchers who study male elephants attributed the young males’ abnormal behavior to their surging hormones and lack of social learning—both of which were controlled after older male elephants were introduced. In some instances, the orphaned female elephants were also hyperaggressive and attacked tourist vehicles. But they, too, apparently recovered and went on to form family groups, although these groups sometimes include unrelated individuals, which is unusual in elephants.

“On the surface, they look like they’re now getting on okay,” says Karen McComb, a behavioral ecologist at the University of Sussex in the United Kingdom and a co-author of the study. “But we found a way to go deeper into their minds, and that’s how we found the deficits in the social decisions that they make.”

From studies of the relatively undisturbed population of elephants in Kenya’s Amboseli National Park, scientists know that social learning is important to these animals. In their family groups, the oldest female is the guiding matriarch, and she passes on to younger members behaviors such as how to greet family members and how to react to the calls of strange females.

The researchers compared the reactions of 14 Pilanesberg elephant families and 39 elephant families in Amboseli to different levels of social threats. For each test, they positioned their Land Rover 100 meters away from a family group and broadcast an elephant’s deep-throated greeting call for 10 to 20 seconds. The calls were from familiar or unfamiliar elephants or were resynthesized calls that were made to sound like individuals of specific age classes. (You can listen to examples here.) These tests gauged the elephants’ ability to make the best decision when faced with what could be a major threat: an older, dominant, strange female. Such animals can pose a danger to a family by forcing them, for instance, to leave areas where they are feeding, McComb says.

The scientists video-recorded the families’ reactions to the various calls and measured certain key behaviors, such as whether the elephants defensively bunched together, whether they listened and smelled for the stranger, and how much time they spent doing these activities.

When the researchers played the calls to the Amboseli elephants, almost every family responded appropriately to the rumbles of the older, unfamiliar female. Typically, the entire family froze in place. The members raised their ears to listen and their trunks to sniff for the invader. They turned toward the vehicle and bunched together, forming a fortress of elephant flesh with the matriarch in front. Sometimes, they charged past the scientist’s vehicle, searching for the alien hussy. “You get the feeling they really know what they’re doing,” McComb says. “They have very coordinated responses.”

In contrast, the Pilanesberg elephants never seemed to know what to do. “The pattern there was no pattern at all; their reactions were completely random,” McComb says. In one extreme instance, a family left the area at once, traveling more than a kilometer before they came to a halt—but they did so in response to the call of an elephant they all knew. “Yet when they heard the call of the older, strange female, they did nothing at all; they just stayed completely relaxed,” Shannon says.

“You might think because of their history that they were just more accepting of strangers,” McComb says. “But it wasn’t that. They simply failed at picking out the calls of older, socially dominant animals.”

Because the Pilanesberg elephants grew up without the social knowledge of their original families, they will likely never properly respond to social threats and may even pass on their inappropriate behaviors to the next generation, the team concludes in the current issue of Frontiers in Zoology. And it may be that elephant populations that are heavily poached or otherwise adversely affected by human activities are similarly socially damaged, they say.

All of this matters because poor decision-making can affect the elephants’ reproductive success, McComb says. A previous study that she and others carried out in Amboseli compared the decision-making abilities of younger and older matriarchs. Those families led by the oldest individuals with the most experience also had the most calves. Exactly how the poor decisions of the Pilanesberg elephants will affect them in the future is as yet unknown. “What we now know is that their social understanding is most certainly impaired,” McComb says.

The team’s findings “may also apply to other species, such as cetaceans and nonhuman primates” that have been and, in some cases, continue to be heavily managed, Marino says. They also show “unequivocally that conservation that is only based on numbers,” that is, on how many animals are in a population, “and which does not take into account the individual ends in disaster.”

Richard Connor, a cetacean biologist at the University of Massachusetts, Dartmouth, adds: “It is difficult to not conclude that the legal killing or illegal poaching of elephants is not only inhumane, it is barbaric.”