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Chimpanzees Spotted Fishing For Crabs May Hold Clues About Human Evolution

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A new study from Kyoto University described how mother and child chimpanzees (not pictured) in West Africa engage in freshwater crab-fishing. Researchers believe such behavior can help explain how ancient humans picked up the crabbing skill themselves.  ( Sasin Tipchai | Pixabay )

Scientists in Japan have observed chimpanzees fishing for crabs in the wild, which is the first instance such behavior was seen in the animals.

In a study featured in the Journal of Human Evolution, researchers from Kyoto University described how chimpanzees in Guinea, West Africa practiced freshwater crab fishing as a way to find food. This behavior was primarily seen among mother and child primates living in rainforests in the region's Nimba Mountains.

The team believes such a complex activity among chimpanzees in the wild may hold clues as to how early humans learned how to fish a long time ago.

"The aquatic fauna our ancestors consumed likely provided essential long-chain polyunsaturated fatty acids, required for optimal brain growth and function," said Kathelijne Koops, a researcher from the University of Zurich and lead author of the study.

Koops, who is also part of the Leading Graduate Program in Primatology and Wildlife Science at Kyoto University, explained that their findings point to aquatic fauna as an integral part of early humans' diet and not just an occasional substitute.

Crab Fishing As A Year-Round Activity

Koops and her colleagues first observed freshwater crab fishing among chimpanzees in 2012. They collected various data such as the demographics and various behavior associated with such an activity. They also analyzed the nutritional value of crabs and compared it to other food that the chimpanzees typically ate.

Through their observations, the researchers learned that crabbing was not just a year-round practice among the chimpanzees, but it also negatively correlated with the primates' tendency to consume ants as part of their diet.

Mother and child chimpanzees often fished for crabs regardless of the season, or the availability of other food such as fruits in their area.

Meanwhile, adult male chimpanzees preferred to stick to their regular diet of ants and were least likely to eat crabs and other aquatic fauna.

Koops said large crabs and ants provide basically the same levels of energy and sodium. This led them to believe that female chimpanzees use crabs as an important source of protein and salts all throughout the year, especially when they are pregnant or nursing. It also provides nourishment for younger chimps as they continue to grow.

Link To Human Evolution

The results of the study can help shed more light into human evolution. Such behavior among man's closest genetic relatives suggests that fishing may not be limited by habitat as researchers initially thought.

Tetsuro Matsuzawa, Koops's fellow researcher and co-author of the study, said it is not the first case where non-human primates were observed eating crabs. However, their research presents the first evidence of apes other than humans engaging in such behavior.

Before the Kyoto University study, Matsuzawa pointed out that consumption of aquatic fauna was initially seen among monkey species living near bodies of water, such as lakes, rivers, or coastlines, and not among those living in closed rainforests.

"It's exciting to see a behavior like this that allows us to improve our understanding of what drove our ancestors to diversify their diet," he said.

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