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Feeding Behavior In Monkeys, Humans Have Ancient, Shared Roots

May 20, 2009

Behavioral ecologists working in Bolivia have found that wild spider monkeys control their diets in a similar way to humans, contrary to what has been thought up to now. Rather than trying to maximize their daily energy intake, the monkeys tightly regulate their daily protein intake, so that it stays at the same level regardless of seasonal variation in the availability of different foods.

Tight regulation of daily protein intake is known to play a role in the development of obesity in humans, and the findings from this research suggest that the evolutionary origins of these eating patterns in humans may be far older than suspected. Until now it was thought humans’ eating patterns originated in the Palaeolithic era (between 2.4 million and 10,000 years ago).

The research, published online today (Wednesday 20 May) in the journal Behavioral Ecology, also provides valuable information about which trees are important for the monkeys’ diet, which is relevant to conservation; in addition, it may help to improve the care of captive primates, which can be prone to obesity and related health problems due to their diet.

Dr Annika Felton, a Departmental Visitor at the Fenner School of Environment and Society, The Australian National University, Canberra, Australia, spent a year in the Bolivian rainforest (in Departmento Santa Cruz) familiarizing the Peruvian spider monkeys (Ateles chamek) to her presence and then observing their feeding habits.


Dr Felton said: “We found that the pattern of nutrient intake by wild spider monkeys, which are primarily fruit eaters, was almost identical to humans, which are omnivores. What spider monkeys and humans have in common is that they tightly regulate their daily protein intake, i.e. they appear to aim for a target amount of protein each day, regardless of whether they only ate ripe fruit or mixed in other vegetable matter as well. Finding this result in spider monkeys was unexpected because, previously, ripe fruit specialists were thought to be ‘energy maxi misers’. In other words, they would aim to maximize their daily energy intake. Our findings show this is not the case.


“Our findings are also interesting from an evolutionary point of view. Similarity in the regulatory pattern of protein intake between distantly related species, such as humans and spider monkeys, possessing very different dietary habits, may indicate that the evolutionary origins of such regulatory patterns are quite old, potentially far older than the Palaeolithic era. If we are not dealing with convergent evolution here ““ in other words that spider monkeys and humans have evolved this trait independently ““ then this trait may have been shared by our common ancestor. Spider monkeys are New World primates that split from the Old World primates about 40 million years ago.

“Finally, our research shows that nutritionally-balanced food sources that are used extensively by a wild population may need special attention in terms of conservation planning, perhaps by regulating logging and selecting certain tree species for re-planting. The majority of the monkeys’ nourishment was sourced from a species of fig tree, Ficus boliviana, that is currently being harvested for timber in Bolivia.”

Dr Felton and her colleagues found that the monkeys ate a wide variety of fruit and vegetables ““ 105 different plants belonging to 63 species during the 12 months of observation. Figs were particularly popular. The monkeys rarely ate insects, which are rich in protein.






* Protein content of diets dictates the daily energy intake of a free-ranging primate. Behavioral Ecology. Published online under advance access. doi:10.1093/beheco/arp021

Image Caption: This is a curious “teenage” (sub-adult) male spider monkey. Credit: Annika Felton

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