Most species, including baboons, humans, and horses, exhibit a shared characteristic: the experience of early adversity often leads to subsequent hardships later in life.
When researchers from the Dian Fossey Gorilla Fund and the University of Michigan initiated a study on gorillas, they harbored uncertainty regarding the eventual findings.
Previous studies conducted by the Fossey Fund unveiled the unexpected resilience of young gorillas in coping with the loss of their mothers, a distinction observed in many other species. Nonetheless, the loss of a mother represents merely one among various potential challenges encountered by young animals.
According to U-M anthropologist Stacy Rosenbaum, the senior author of the study, surviving early life adversity typically results in poor health, reduced fertility, or a shorter lifespan, irrespective of the species. A range of detrimental consequences appears to affect individuals throughout their adult lives.
In contrast to their expectations, the researchers observed that gorillas who surpassed the age of 6 exhibited minimal impact from the difficulties encountered during their infancy and adolescence. The study has been published in the journal Current Biology.
Similarly, humans, like other species, confront early life adversity which can have enduring effects such as a reduced lifespan or health complications, as elucidated by Rosenbaum. However, discerning whether events in early life directly cause cancer or premature death in adults remains challenging, as it may be influenced by a combination of behavioral, environmental, and cultural factors.
Analyzing early adverse events in non-human species could furnish insights into their effects on humans and potential strategies for alleviation.
Robin Morrison, a researcher with the Dian Fossey Gorilla Fund and the lead author of the study, emphasized the advantage of studying animals to eliminate variations found in human populations. Animals share similar diets, engage in regular exercise, and lack opportunities for behaviors such as smoking that yield adverse health outcomes.
Despite these similarities, early adversity in most species still exerts negative effects in adulthood, implying the existence of incompletely understood deeper biological mechanisms, as underscored by Morrison. The distinct pattern observed in gorillas suggests the potential to overcome early life adversities. Comprehending the reasons underlying this resilience holds substantial implications for our own species.
Gorillas, akin to humans, possess an extended lifespan and invest significantly in a limited number of offspring. This renders them an ideal animal model for comprehending the consequences of early life adversity. The researchers examined 55 years of long-term data collected from 253 wild mountain gorillas, comprising 135 males and 118 females. These gorillas reside in Volcanoes National Park in Rwanda and have been under the monitoring of the Dian Fossey Gorilla Fund for over five decades.
The researchers identified six distinct types of early life adversity, such as the loss of a father or mother, the death of a group member due to infanticide, social group instability, a scarcity of peers in the social group, and the presence of a competing sibling born shortly after them. The data encompassed information on the number and timing of these early adversities experienced by each gorilla, as well as their lifespan.
They examined the outcomes when gorillas encountered none, one, two, or three or more adverse events. The findings revealed that the greater the number of adverse events experienced by gorillas before the age of 6, the higher the likelihood of mortality during their juvenile stage. However, if they survived beyond the age of 6, regardless of the number of adverse events, there was no evidence suggesting a shorter lifespan.
Interestingly, if a gorilla encountered three or more forms of adversity, it actually lived longer, experiencing a 70% reduction in the risk of death throughout its adult life. This trend was primarily driven by increased longevity in males, and the researchers speculate that it may be attributable to a phenomenon known as viability selection.
This phenomenon suggests that if a gorilla possesses enough strength to survive challenging events in early life, it may exhibit higher-quality traits, making it more likely to enjoy a longer lifespan.
Rosenbaum shared her initial expectations, stating, “I anticipated that these gorillas would have shorter lifespans and face difficulties as adults. However, our findings indicate that while these events indeed increase the risk of mortality during youth, there is no evidence to suggest a shortened lifespan if gorillas survive beyond the age of 6. This stands in stark contrast to what we observe in other species.”
The researchers put forward several theories to explain the remarkable resilience of mountain gorillas. These primates form tightly-knit social groups, and previous studies have demonstrated that when a young gorilla loses its mother, it does not become isolated. Instead, other gorillas step in to provide companionship and support.
Morrison explained, “Following the loss of their mothers, these young gorillas actually spend more time with other gorillas, particularly the highest-ranking adult male, irrespective of biological paternity. These strong social networks may offer crucial buffering effects, as observed in humans. The quality of our social relationships plays a vital role in predicting our health and longevity, sometimes surpassing the significance of genetics or lifestyle factors.”
Another factor that may contribute to gorillas’ resilience is their habitat. Mountain gorillas inhabit resource-rich environments compared to many other wild primate species. This abundance of food and water may make it easier for gorillas to overcome challenging circumstances without the added stress of scarcity, as explained by Rosenbaum.
“For comparison, savanna baboons, which served as the inspiration for our analysis, live in highly seasonal environments characterized by extreme droughts. They often have to travel long distances to access water sources and constantly struggle to obtain sufficient calories. This is not the world in which mountain gorillas reside. They are often described as living in a giant salad bowl.”
The findings of this study suggest that species similar to humans can exhibit significant resilience in the face of early life adversity. The results also raise important questions about the biological mechanisms underlying sensitivity to early experiences and the protective factors that contribute to resilience in gorillas.
Rosenbaum emphasized, “We should not assume that the long-term negative effects of early life adversity universally apply. We often discuss this as a common experience, assuming that adulthood will inevitably be compromised for those who endure early adversity. However, the data are far more complex in both human and non-human species. This research presents a hopeful narrative.”
Study: Cumulative early life adversity does not predict reduced adult longevity in wild gorillas
About the Dian Fossey Gorilla Fund
Established in 1967, the Dian Fossey Gorilla Fund is the world’s oldest and largest organization exclusively dedicated to gorilla conservation. With over 300 staff members in Rwanda and eastern DR Congo, the Fossey Fund protects vulnerable gorilla populations and some of the planet’s most biodiverse regions. Their holistic conservation approach includes supporting local communities’ livelihoods and food security while nurturing the capacity of African conservationists.