Humans aren’t the only impulsive risk-takers in their youth. Other animals behave badly, and it’s a vital part of their education, explains Jason Goldman.
If you are an otter who wants to play a game of “chicken”, then perhaps the best place to head for is a patch of ocean that stretches south of the San Francisco Bay towards the Farallon Islands. As explained by Barbara Natterson-Horowitz and Kathryn Bowers in their book Zoobiquity, this treacherous bit of sea is known as the "triangle of death" for good reason – the considerable threat of great white sharks is increased by the conspicuous absence of kelp that otters normally use to hide. Add dangerous currents and sharp rocks, and a shark has the perfect recipe for a sea otter snack. Oh, and the waters are teeming with the dangerous parasite Toxoplasmosa gondii.
Doting otter parents do their best to keep juveniles from venturing into the triangle of death, and mature males and females are smart enough to stay away. In fact, females never show up in the area at all. The only otters foolish enough to attempt an incursion into the triangle are adolescent males – it turns out that human teenagers aren't the only animals that make bad decisions during the awkward transition between childhood and maturity.
Not to be outdone by sea otters, young Thomson's gazelles (Gazella thomsoni) make their own kinds of risky decisions. When a group of gazelles detects nearby stalking predators such as cheetahs or lions, zoologist Clare FitzGibbon discovered that instead of running they sometimes approach and follow the predator, sometimes for more than seventy minutes. It’s thought this sort of reverse stalking behaviour, which is also common in fish and birds, reduces the risk of being attacked. Lions and cheetahs stalk before they ambush prey, and if the gazelle make clear their awareness of the predator’s presence, it may delay its next hunting attempt. This behaviour is only seen with predators who use a stalk-and-ambush strategy – gazelle do not follow hyena, despite the fact that more gazelle die from predation by hyenas than by cheetahs or lions.
While it isn't only the juveniles who follow their predators – adults do it too – the younger gazelle face a much higher risk. The probability of being killed while following a cheetah is one in 5,000 for mature gazelle, but only one in 417 for teenagers. Despite the incredibly high risk, predator following has persisted over evolutionary time. Perhaps, Natterson-Horowitz and Bowers suggest, it provides the adolescent gazelles with an opportunity to learn more about their predators, allowing them to better predict future encounters with cheetahs and lions.
Boyz n the hood
This falls in line with the current thinking in humans; scientists say that teenagers’ impulsive, infuriating traits may be the key to success when they are adults. Human teenagers don't die at the hands (or jaws) of predators, like adolescent otters or young gazelle, but their risks come in other ways. In the United States, according to the Centers for Disease Control, one third of teenage deaths are associated with car crashes. Another leading cause of death among adolescent human males is homicide, representing 13% of deaths for that age group. But the risk of death is not evenly distributed among teenagers. Like otters, males are more likely to die than females, for every year between the age of 12 and 19, and older teenagers are more likely to die than younger teenagers.
African elephants (Loxodonta africana) also have a period of adolescence that lasts about a decade, between the ages of 10 and 20. During this period of transition, male elephants leave the female-dominated groups into which they were born, and spend their adolescence in all-male groups. While elephant males become sexually mature by age 17, they usually don't successfully mate until their late 20s or early 30s, after their first musth, a period of pronounced sexual activity in male elephants which is the result of especially high levels of testosterone. Despite being sexually mature by their late teens, males don't typically undergo musth in all-male elephant groups for at least another decade, and elephant teenagers generally behave themselves.
But a peculiar group of teenage males in South Africa paints quite a different picture. As these elephants aged out of adolescence, they began successfully breeding by age 18, a full decade before what is ordinary for their species. For typical 25-30 year olds, musth lasts for several days, while for forty-year-olds it may last as long as four months. But the period of musth in these teenage males lasted as long as five months, and it wasn't only their sexual behaviours that puzzled researchers. They also went on killing sprees, targeting white rhinoceroses in particular.
What made these male elephants so dangerously aggressive and so unusually sexually active? When the young were growing up in South Africa's Kruger National Park in the 1980s, the mature males and females of their social groups were the victims of culling programmes. The juvenile males, none of them older than ten years, were relocated to Pilanesberg National Park some six hundred kilometres away, where they matured in the absence of any adults. The orphan males never spent their awkward teenage years being mentored by older, more experienced males. An assessment of this and other "stressed communities" which had all been subject to elephant culling showed that male-male aggression accounted for almost ninety out of every hundred male deaths, compared with only 6% in unstressed communities.
Rob Slotow, of the University of Natal in South Africa, explains than when given a chance to grow up surrounded by mature adult males, the younger, rebellious teenagers are kept in line by the elder pachyderms. The adolescents "lose the physical signs of musth minutes or hours after an aggressive interaction with a higher-ranking musth male… larger, older males may delay the onset of musth in younger males." The orphans of Pilanesberg did not have this safety net.
Slotow and colleagues tested this by introducing six older males into the Pilanesberg community, and what they found was remarkable. The amount of time spent in musth was reduced for all the Pilanesberg orphans who suddenly found themselves subordinate to the newly introduced males. The wanton slaughter of white rhinoceroses was eliminated entirely. It seems as if elephant society evolved to account for the bad decisions associated with adolescence, by having older males suppress the hypersexuality and hyperaggressiveness of younger males.
Throughout the animal kingdom, adolescence is a tightrope act. As they gradually lose the care and protection they receive from their parents, young animals of any species must strike a delicate balance between risk and safety. If they play it too safe, they'll suffer a lack of understanding about the dangers of the worlds in which they live. Too risky, and they might wind up served as a tasty snack for a hungry shark or cheetah or killed at the hands of their friends.
Most efforts to establish the root of risky decisions made by human teenagers focus on the underdeveloped prefrontal cortex, the part of the brain responsible for mental processes like long-term planning and judgement. But risky decisions are a recurring feature of adolescence for species after species, including many with much smaller prefrontal cortices to begin with, compared to humans or elephants. Perhaps concerned human parents can rest a bit easier knowing that their worries echo throughout the animal kingdom. If sea otter parents could, you can be sure they too would punish their offspring for breaking curfew and staying out too late in the triangle of death. Without even so much as a phone call.