Most species, including humans, who experience early life adversity suffer as adults, but gorillas break the mould, new research suggests.
Previous studies by the Dian Fossey Gorilla Fund revealed that young gorillas are resilient to losing their mothers, in contrast to what has been found in many other species.
However, losing their mother is only one of many bad things that can potentially happen to young animals, researchers say.
I don't think we should assume that the long-term negative effects of early life adversity are universal— Stacy Rosenbaum, University of Michigan
Senior author Stacy Rosenbaum, a University of Michigan anthropologist, said: “Assuming that you survive something that we consider early life adversity, it’s often still the case that you will be less healthy or you will have fewer kids or your lifespan will be shorter – no matter what species you are.
“There’s this whole range of things that happens to you that seems to just make your life worse in adulthood.”
Instead, the researchers found that gorillas who survived past the age of six were largely unaffected by difficulties they encountered as infants or juveniles.
In humans, it is difficult to establish whether we, for example, develop cancer or die early as adults because of an adverse event – such as the death of a parent or sibling – early in life, or whether it is because of a multitude of behavioural, environmental and cultural factors or a combination of all of the above.
Researchers suggest studying these early adverse events in non-human species could help them understand how such events affect humans, and how to mitigate them.
According to the study, the findings that gorillas show a different pattern suggests early life adversities can be overcome.
Understanding why and how this happens can have significant implications for humans, the researchers suggest.
The study looked at 55 years of long-term data collected in 253 wild mountain gorillas, 135 of which were male and 118 female.
These animals live in Volcanoes National Park in Rwanda, and have been monitored for more than five decades by the Dian Fossey Gorilla Fund.
Researchers identified six different kinds of early life adversity – losing a father or mother, experiencing the death of a group member by infanticide, social group instability, having few age-mates in the social group, and having a competing sibling who was born soon after them.
The researchers looked at what happened when a gorilla experienced none, one, two or three or more adverse events.
They found that the more of these adverse events gorillas experienced before the age of six, the more likely they were to die as juveniles.
However, if they experienced early adversity, but survived until age six, there was no evidence their lifespans were shorter, no matter how many adverse events they suffered.
According to the study, 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 across adulthood.
The study found 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 was strong enough to survive difficult early life events, it might just be a higher-quality individual, and therefore more likely to have a longer lifespan.
Assistant Professor Rosenbaum, said: “I was expecting to see that these gorillas would have short lifespans and would not do very well as adults.
“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 six, there’s no evidence that those shorten your lifespan at all. This is quite different from what we see in other species.”
She added: “I don’t think we should assume that the long-term negative effects of early life adversity are universal.
“We tend to talk about this as if it’s a ubiquitous experience, and a given that your adulthood is going to be compromised if you live through early adversity.
“But I don’t think it’s nearly that cut and dry, even in the human literature.”
The researchers have some theories about why these mountain gorillas were so resilient.
The animals have very tight-knit social groups and prior studies have shown that when a young gorilla loses its mom, it does not actually become more isolated, as other gorillas fill the gap.
The study is published in the journal Current Biology.
