Study of 'nearest human relative' suggests parenting more influential than genetics

A new study of chimpanzees has underlined the importance of parenting and downplayed the influence of inherited traits on the health and wellbeing of young.

An international team of biologists, led by researchers from Liverpool John Moores University, the Max Planck Institute for Evolutionary Anthropology, the Weizmann Institute of Science, and Institut des Sciences Cognitives, found that the influence of their mothers combined with the nurturing environment of the animal community best explain physiological stress patterns in wild chimpanzees. Stress is known to influence health and survival in many primates, including humans.

Their results, published in Nature Communications Biology, suggest that the role of genetics may have been overstated in previous research.

Dr Patrick Tkaczynski, a behavioural ecologist at LJMU, said nature versus nurture was now known as a false dichotomy within evolutionary biology: “Yet it can be challenging to disentangle genetic and parental effects from the shared environmental effects,” he said.

“To that end, we were unable to find any clear evidence of a genetic influence on the stress levels of the chimpanzees. Rather our results suggest it is the nurturing environment of the communities you live in, and the mothers you are born to, which are more important for chimpanzees and potentially other long-lived animals, such as ourselves.”

Using a unique long-term dataset comprising 18 years of research on five communities of wild chimpanzees, the team examined more than 6,000 urinary samples from 170 animals, collected non-invasively from leaves and the ground. Urinary cortisol concentrations are a well-established proxy for the physiological stress of chimpanzees.

Chimpanzees make ideal models for studying cortisol patterns because, similar to humans, they exhibit relatively long juvenile phases and maternal associations that may allow for more adjustment of phenotypes to social and environmental circumstances.

Analysis of the samples showed that shared community effects explained the majority of variation in cortisol levels. Although all chimpanzees demonstrated fluctuations in their cortisol levels due to variation in socioecological factors, the team observed stable individual differences in average cortisol levels lasting over many years.

“Importantly, when we focused on within-group variation, maternal effects were the primary heritable factor shaping average cortisol levels. We found that non-genetic maternal effects explain ~8% of the variation in this trait, while variation attributable to genetic factors was not clearly distinguishable from zero,” said co-lead author Dr Fabrizio Mafessoni, currently at the Weizmann Institute of Science.

“This is significant and unexpected, as previous human studies have suggested as much as 60% of variation may be explained by genetics. However, these studies could not quantify shared environmental variables to the level of detail we can in chimpanzees.”

“Our results offer a new perspective on physiological plasticity in social, long-lived species, including humans. These results should encourage human researchers to take a community rather than an individual-level approach to understanding and reducing stress exposure,” concluded Prof Catherine Crockford, senior author and co-director of The Great Ape Social Mind Lab, based in Institut des Sciences Cognitives.