There is something that most species, from baboons to humans to horses, have in common: when they suffer severe adversity early in life, they are more likely to experience hardship later in life.
When researchers from the Dian Fossey Gorilla Fund and the University of Michigan decided to look at this question in gorillas, they weren’t sure what they would find.
Previous studies from the Fossey Fund revealed that young gorillas are surprisingly resistant to losing their mothers, in contrast to what has been found in many other species. But losing your mother is just one of many potentially bad things that can happen to young animals.
“Assuming you survive something that we consider to be an early adversity in life, it often remains the case that you will be less healthy or have fewer children or your life expectancy will be shorter, no matter what species you are,” said the anthropologist. from UM Stacy. Rosenbaum, lead author of the study. “There’s a whole range of things that happen to you that seem to make your life worse as an adult.”
But instead, the researchers found that the gorillas that survived past the age of 6 were largely unaffected by the difficulties they encountered as infants or youngsters. The study is published in the journal Current Biology.
Like other species, humans also deal with adversity early in life, and the effects of this can follow us into adulthood, such as a shorter life span or health complications, Rosenbaum said. But in humans, it is difficult to determine whether, for example, we develop cancer or die early as adults due to an adverse event early in life per se, or whether it is due to a multitude of behavioural, environmental and cultural factors, or a combination. of all of the above.
Studying these early adverse events in non-human species could help researchers understand how these events affect humans and how to mitigate them.
“When you look at animals, you remove a lot of the variation that we have in humans. For example, they all have similar diets, they all exercise as part of their daily lives, they don’t have the opportunity to engage in behaviors with negative health outcomes. such as smoking,” said Robin Morrison, a researcher at the Dian Fossey Gorilla Fund and lead author of the study.
But despite this, in most species it is still the case that early adversity can have negative effects in later life, suggesting that there is some kind of deeper biological mechanism that we don’t quite understand, Morrison said. That gorillas show a different pattern suggests that these early life adversities can be overcome. Understanding why and how this happens may have significant implications for our own species, he said.
Just like humans, gorillas live a long time and have a small number of offspring that they invest heavily in. This makes them a good comparative animal model for understanding the ramifications of adverse events in early life. The researchers analyzed 55 years of long-term data collected on 253 wild mountain gorillas, 135 of which were male and 118 female. These gorillas live in the Volcanoes National Park in Rwanda and have been monitored for more than five decades by the Dian Fossey Gorilla Fund.
The researchers identified six different types of early life adversity: losing a parent, experiencing the death of a group member by infanticide, social group instability, having few age peers in the social group, and having a sibling. competitive that was born early. after them. The data included information on how many of these early adversities each gorilla experienced and at what age, as well as how long each gorilla lived.
The researchers looked at what happened when a gorilla experienced none, one, two, or three or more adverse events. They found that the more adverse events the gorillas experienced before the age of 6, the more likely they were to die when they were young. But if, despite experiencing early adversity, they survived to age 6, past their juvenile stage, the researchers found no evidence that their life expectancy was shorter, no matter how many adverse events the gorillas suffered.
In fact, if a gorilla experienced three or more forms of adversity, it actually lived longer; this group of animals had a 70% reduction in the risk of death during adulthood. But this was driven by greater longevity in males specifically, and the researchers suspect the trend was due to something called viability selection. This means that if a gorilla were strong enough to survive the difficult events of early life, it might simply be a “higher quality individual” and therefore more likely to live longer.
“I expected to see that these gorillas would have short lives and not do very well as adults,” Rosenbaum said. “We found that these events are definitely associated with a much higher risk of death when you’re young. But if you survive to age 6, there’s no evidence that they shorten your lifespan. This is quite different from what we see in other species.”
Researchers have a few theories as to why these mountain gorillas were so hardy. Gorillas have tight-knit social groups, and previous studies have shown that when a young gorilla loses its mother, it doesn’t actually become more isolated: other gorillas fill the gap in social companionship.
“The young actually increase their time around other gorillas after the loss of their mother and, in particular, the highest-ranking adult male, even if he is not their biological father,” Morrison said. “These robust networks could provide critical social cushioning, as has been shown in humans. The quality of our social relationships is a very important predictor of our health and longevity, in some cases more important than genetics or lifestyle.” .
Another reason why they may be relatively protected from the consequences of adversity is that mountain gorillas live in a resource-rich environment compared to many other wild primates. It can be easier for a gorilla to survive in difficult circumstances if it’s not constantly dealing with the stress of finding enough food and water, Rosenbaum said.
“For comparison, the savannah baboons, which were the inspiration for this analysis, live in this highly seasonal environment where they experience extreme droughts. They sometimes have to walk miles to reach a water hole. They often struggle to find every calorie they eat,” he said. “That’s not the world mountain gorillas live in. They are often described as living in a giant salad bowl.”
The researchers’ findings suggest that species similar to our own may have significant resistance to adversity in early life. The results also raise important questions about the biological roots of sensitivity to early experiences and the protective mechanisms that contribute to resilience in gorillas.
“I don’t think we should assume that the long-term negative effects of early life adversity are universal,” Rosenbaum said. “We tend to talk about this as a pervasive experience and a fact that your adulthood will be compromised if you experience early adversity.
“But I don’t think it’s that straightforward, even in the human literature. I think the data is much more complex for humans, and this research would suggest that it might be more complex for other animals as well.” And I actually think that’s a hopeful story.”
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