05-15-2023

Does early life adversity in gorillas lead to hardship as adults?

A fascinating new study has emerged that challenges the common belief across various species – from humans to horses to baboons – that early life adversity results in a higher likelihood of experiencing hardship later in life.

This groundbreaking research was conducted by a team from the Dian Fossey Gorilla Fund and the University of Michigan who decided to investigate this question in gorillas, unsure of what they might discover. 

image Credit: Dian Fossey Gorilla Fund

Previous studies conducted by the Fossey Fund showed that young gorillas displayed an incredible resilience after losing their mothers – a stark contrast to other species. However, the loss of a mother is only one form of adversity that young animals can face.

Senior author on the study, Stacy Rosenbaum, an anthropologist from the University of Michigan, remarked: “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.” 

How the research was conducted

Rosenbaum noted that there is a wide range of negative impacts that early life adversity can have on adulthood.

The researchers, however, were surprised to find that gorillas who survived past the age of six were largely unaffected by the hardships they faced as infants or juveniles. This crucial finding has been published in the prestigious journal, Current Biology.

Rosenbaum compared this phenomenon to humans, who also experience early life adversity that can lead to issues in adulthood, such as health complications or a shortened lifespan. 

However, in human studies, it’s a challenge to determine whether these outcomes are directly due to early life adversity, or if they stem from a combination of behavioral, environmental, and cultural factors. 

Studying these events in non-human species, such as gorillas, may provide valuable insights to help understand and mitigate these effects in humans.

image Credit: Dian Fossey Gorilla Fund

Robin Morrison, a researcher with the Dian Fossey Gorilla Fund and the lead author on the study, described the benefits of studying animals in this context. 

“When you look at animals, you remove a lot of the variation that we have in humans. For example, they are all eating similar diets, they all get exercise as part of their daily lives, they don’t have the opportunity to engage in behaviors with negative health outcomes like smoking,” explained Morrison.

Despite this, most species still suffer negative effects in adulthood from early adversity, suggesting an underlying biological mechanism that is not yet fully understood. The differing pattern observed in gorillas, however, indicates that it’s possible to overcome these adversities. 

Morrison believes that understanding how this resilience works could have important implications for our own species.

Why use gorillas for the study?

The researchers chose gorillas for this study as they, like humans, have a long lifespan and invest heavily in a small number of offspring. The research team analyzed 55 years of long-term data collected on 253 wild mountain gorillas – 135 males and 118 females – living in Volcanoes National Park in Rwanda. These gorillas have been under the continuous observation of the Dian Fossey Gorilla Fund for over five decades.

The study identified six different types of early life adversity, including losing a parent, experiencing the death of a group member through infanticide, social group instability, having few age-mates in the social group, and having a sibling born soon after them. The data showed how many of these adversities each gorilla faced and at what age, as well as their lifespan.

What the researchers discovered

The researchers found that gorillas who experienced more adversities before the age of six were more likely to die as juveniles. However, if they survived past their juvenile stage, their lifespan was not shortened, regardless of how many adversities they faced. 

Surprisingly, gorillas who faced three or more adversities actually lived longer, with a 70 percent reduction in the risk of death in adulthood. This intriguing trend was primarily seen in males, leading researchers to theorize that it may be linked to a phenomenon known as viability selection. 

In essence, this means that a gorilla robust enough to endure tough early life events might be a “higher-quality individual” and consequently more likely to enjoy a longer lifespan.

“I was expecting to see that these gorillas would have short lifespans and would not do very well as adults,” said Rosenbaum.

“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 at all. This is quite different from what we see in other species.”

Mountain gorillas exhibit incredible resilience

The team has a few theories to explain the extraordinary resilience of these mountain gorillas. For one, gorillas live in very close-knit social groups, and previous studies have shown that when a young gorilla loses its mother, other group members step in to fill the void in social companionship.

“The youngster actually increases its time near other gorillas after the loss of its mom and in particular the highest-ranking adult male, even if he isn’t their biological father,” said Morrison.

“These strong networks might provide critical social buffering, 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 factor contributing to their resilience may be the resource-rich environment mountain gorillas inhabit, which is a luxury many other wild primates don’t enjoy. 

“For comparison, savanna baboons – who were the inspiration for this analysis – live in this highly seasonal environment where they go through extreme droughts,” said Rosenbaum. “They sometimes will have to walk miles to get to a water hole. They’re often struggling for every single calorie they take in.” She contrasted this with the world of mountain gorillas, which she described as a “giant salad bowl.”

Conclusion

The findings from this research suggest that species closely related to humans can exhibit significant resilience to early life adversity. It also raises intriguing 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,” said Rosenbaum.

She challenged the ubiquity of this belief, emphasizing that the data is much more complex for humans and other animals. “I actually think that that’s a hopeful story,” Rosenbaum added, indicating a silver lining to the challenges faced in early life. 

This research opens up new avenues for understanding and potentially mitigating the impacts of early life adversity across species, including our own.

More about mountain gorillas

Mountain gorillas are a critically endangered species of great ape, and one of the two subspecies of the eastern gorilla. As of my knowledge cutoff in September 2021, there were only about 1,000 mountain gorillas left in the wild.

Here’s what you should know about mountain gorillas:

Habitat and Distribution

Mountain gorillas live in the high-altitude cloud forests of central Africa, specifically in two isolated regions. One population can be found within the Virunga volcanic mountain range, which stretches across Rwanda’s Volcanoes National Park, Uganda’s Mgahinga Gorilla National Park, and Virunga National Park in the Democratic Republic of Congo. The other population resides in Uganda’s Bwindi Impenetrable National Park.

Physical Characteristics

Mountain gorillas are large and powerfully built, with long, strong arms and a broad chest. Adult males, known as silverbacks due to the characteristic patch of silver hair on their back and hips, typically weigh between 300 and 400 pounds and stand about 4 to 6 feet tall when upright. Females are typically smaller, weighing between 150 and 200 pounds. Mountain gorillas have a robust build with a large head, a prominent brow ridge, and a long, muscular arms.

Behavior and Social Structure

Mountain gorillas are highly social animals, living in stable groups that usually consist of one dominant silverback, multiple females, and their offspring. Groups may also include younger subordinate males, known as blackbacks. Silverbacks lead the group, making decisions about feeding, nesting, and movement.

Mountain gorillas are diurnal, spending most of their day foraging for food and resting. They build new nests from foliage each night.

Diet

Mountain gorillas are primarily herbivorous. They eat a variety of plant species, including leaves, stems, roots, vines, and fruits. They are also known to eat small invertebrates. Their diet varies by season and depends on what food is available.

Reproduction and Lifespan

Female mountain gorillas typically start to breed in their late teens, while males start in their early teens. The gestation period is about 8.5 months, and infants are cared for by their mothers for several years. 

Mountain gorillas have a slow rate of reproduction which, along with other factors, has contributed to their status as a critically endangered species. In the wild, mountain gorillas can live to be over 40 years old.

Threats and Conservation

Mountain gorillas face numerous threats, including habitat loss due to agriculture and human settlement, disease (including diseases transmitted by humans), poaching, and civil conflict. Conservation efforts have included anti-poaching patrols, veterinary care, community education, and ecotourism. These efforts have led to a slow increase in their numbers, but mountain gorillas remain critically endangered.

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