Studying ape faeces can explain why humans breastfeed for such a short time

Breaking new ground 21. jul 2021 2 min Assistant Professor Takumi Tsutaya Written by Kristian Sjøgren

New research shows that mapping proteins in faeces can be used to explore the behaviour and ecology of mammals and to determine why humans breastfeed their infants for a rather shorter time than the other large primates.

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Some aspects of animal behaviour are very difficult and costly to map, such as breastfeeding.

With conventional methods, biologists have to be in the field for several months or even years to map breastfeeding in gorillas or orangutans, for example.

However, there may be other ways of doing this.

In a new study, researchers from the University of Copenhagen, Japan and others show that mapping proteins in faeces can provide insight into otherwise hidden aspects of animal behaviour.

“Our main focus area is human development. To understand this, we also have to compare ourselves with the other large primates, and there are interesting and great differences in the time the different species breastfeed their infants. By examining the proteins in faeces, we can obtain better insight into this aspect of species-specific behaviour,” explains a researcher behind the new study, Takumi Tsutaya, Assistant Professor, Department of Evolutionary Studies of Biosystems, Graduate University for Advanced Studies, Hayama, Japan.

The research has been published in Molecular Ecology Resources.

Humans typically breastfeed less than all other primates

People generally breastfeed their babies for 1–3 years. However, this varies considerably, since some mothers breastfeed for just a few months and others up to 6 years. This variation is unique to humans.

Hunter-gathers typically breastfed (and breastfeed for modern hunter-gatherers) their children for 2–3 years.

Chimpanzees breastfeed their young for 4–5 years, and orangutans top the list of mammals by breastfeeding their infants for the first 6–7 years.

“In this context, humans are unique because we breastfeed our children for such a short time. This also affects dietary intake and the composition of intestinal flora plus the immune aspect of the intestinal condition. This is why it is so interesting to study,” says Takumi Tsutaya.

Validating a new method by studying macaques

Takumi Tsutaya and colleagues investigated the possibility of mapping behaviour and intestinal condition by studying the proteins in mammalian faeces.

The researchers used mass spectrometry–based proteomics to map the total composition of proteins in faecal samples from Japanese macaques and compared this with studies of the animals’ behaviour.

They found that this method could very precisely identify when the infant macaques stopped being breastfed and when they started consuming a new diet.

“We examined the proteins that are unique to breast-milk. Identifying them in a faecal sample from young monkeys tells us that they are still breastfeeding. This is an easy and non-invasive way to obtain insight into animal behaviour. Similarly, we can study proteins from different foods and discover more about when the animals start consuming a different diet and what they eat,” explains Takumi Tsutaya.

Studying the immune system by examining proteins in faeces

The protein studies also showed the researchers that they can obtain insight into other parts of the animals’ ecology by using this method.

The researchers could study proteins from the immune system in the intestines, including antibodies and proteins from immune cells such as macrophages. This improves insight into the animals’ immune system, which indicates the animals’ health.

The researchers also studied bacterial proteins in the intestines, which also provide insight into animal health, since the presence of harmful bacteria can be a sign of poor health, and the presence of health-promoting bacteria is a sign of good health.

Collecting faeces from chimpanzees and orangutans

Takumi Tsutaya says that this proof-of-concept study shows that animal behaviour can be studied by examining proteins in their faeces.

The researcher will now use this method on faecal samples collected from wild chimpanzees and orangutans.

The purpose is to determine the situation with breastfeeding and initial diet in the first years of life of these distant relatives. Then the goal is to compare the results with the equivalent for both modern humans and our ancestors.

“The method can be used for all terrestrial mammals, to obtain insight into their dietary habits. Faecal proteomics is a very effective tool for obtaining insight into behaviour that can otherwise take many years to study,” concludes Takumi Tsutaya.

Faecal proteomics as a novel method to study mammalian behaviour and physiology” has been published in Molecular Ecology Resources. Several authors are associated with the Novo Nordisk Foundation Center for Protein Research, University of Copenhagen.

We all live one life, and each of us has a story to tell. If you were born as a hunter-gatherer in the Jomon period or a chimpanzee in the rainforest,...

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