Early-life adversity (ELA) is a major selective force for many taxa, negatively affecting adult outcomes. Researchers examined the effects of six putative sources of ELA on survival, individually and cumulatively, using 55 years of long-term data collected on 253 wild mountain gorillas.
Although cumulative ELA was associated with high mortality in early life, we found no evidence that it had a negative effect on survival later in life.
The Dian Fossey Gorilla Fund and the University of Michigan conducted research on the effects of early-life trauma on gorillas.
Previous Fossey Fund research demonstrated that young gorillas are surprisingly resilient to losing their moms, unlike many other species. However, losing your mother is only one of many potential negative outcomes for young animals.
Stacy Rosenbaum, U-M assistant professor of anthropology and senior author of the study, 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.”
She also said, “There’s this whole range of things that happens to you that seems just to make your life worse in adulthood.”
They discovered that gorillas who lived over the age of six were mostly unaffected by the problems they faced as newborns or juveniles. Titus became a fantastic leader despite losing his mother, brother, and mother before the age of four, keeping his dominant status for two decades.
According to Rosenbaum, Humans, like other creatures, face adversity in childhood, and the consequences can last into maturity, such as a reduced lifespan or health difficulties.
However, it is difficult in humans to determine whether we get cancer or die as adults due to a single unfavorable event or a mixture of behavioral, environmental, and cultural factors—or a combination of all of the above.
The findings, published in the journal Current Biology, could help researchers understand how such catastrophes affect humans and how to mitigate them. Segasira lost both his parents before the age of four. However, at the age of seventeen, he has just established himself as the leader of a group.
Researcher said, “When you look at animals, you lose a lot of the variation that humans have.”
Robin Morrison, Dian Fossey Gorilla Fund researcher and study lead author, said, “For example, they all eat similar diets, they all get exercise as part of their daily lives, and they don’t have the opportunity to engage in behaviors with negative health outcomes like smoking.”
Gorillas are an excellent comparative animal model for understanding the consequences of traumatic early life events. Researchers examined 55 years of long-term data collected from 253 wild mountain gorillas, 135 of whom were male and 118 of whom were female.
They identified six types of early life adversity: losing a father or mother, seeing the infanticide death of a group member, social group instability, having few age-mates in the social group, and having a rival sibling born soon after them. The information included how many of these early difficulties each gorilla faced and when and how long each gorilla lived.
The researchers discovered that the more of these negative occurrences gorillas experienced before age six, the more likely they were to die as juveniles.
However, if they lived until age 6, the researchers found no evidence that their lifespans were shortened, whatever how many negative experiences the gorillas experienced. The Dian Fossey Gorilla Fund’s 55-year database discovered that gorillas who survived early difficulties, such as parental death or social group instability, yet lived until six did not suffer long-term repercussions in adulthood.
This was driven by male longevity, and the researchers believe the trend was caused by a process known as viability selection. Previous research has demonstrated that when a juvenile gorilla loses its mother, it does not grow more isolated: other gorillas cover the gap in social connection. The researchers have some ideas about why these mountain gorillas were so tough.
“I was expecting to see that these gorillas would have short lifespans and would not do very well as adults.” Rosenbaum said.
Morrison 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 those shorten your lifespan. This is quite different from what we see in other species. The youngster increases its time near other gorillas after the loss of its mom, particularly the highest-ranking adult male, even if he isn’t their biological father.”
According to research on humans, these robust networks may offer essential social buffering. In some circumstances, social ties quality is a more significant predictor of health and longevity than genetics or way of life.
Gorillas live in highly close-knit social groups, and previous research has shown that when a baby gorilla loses its mother, other gorillas step in to fill the void in its social support system. Mountain gorillas live longer than humans, which is another factor that may help explain why they are largely insulated from the effects of trauma.
She said, “For comparison, savanna baboons—the inspiration for this analysis—live in this highly seasonal environment where they go through extreme droughts. They sometimes will have to walk miles to get to a water hole. They’re often struggling for every single calorie they take in. That’s not the world that mountain gorillas live in. They’re often described as living in a giant salad bowl.”
Rosenbaum said, “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 will be compromised if you live through early adversity.”
The researcher added, “But I don’t think it’s nearly that cut-and-dry, even in the human literature. I think the data are a lot more complex for humans, and this research would suggest that they might be more complex for other animals, too. And I think that that’s a hopeful story.”
The study results show that species related to our own can be significantly resilient to stress in infancy. The findings also pose significant issues concerning the biological roots of early life sensitivity and the defense systems that support resilience in gorillas.
- Winnie Eckardt, Robin E. Morrison, et.al. Cumulative early-life adversity does not predict reduced adult longevity in wild gorillas. Current Biology. DOI: 10.1016/j.cub.2023.04.051