At some point in human evolution our ancestors began to catch increasing quantities of marine animals which provided them with nutrients which in turn promoted brain development and ultimately helped create modern homo sapiens.
It is not known exactly how this process occurred, but a research team from Kyoto University in Japan has revealed the first ever evidence of wild chimps habitually catching and consuming freshwater crabs.
The findings may provide scientists with new insight into the behaviours which drove our own progress, the scientists suggest.
Writing in the Journal of Human Evolution, the team describes year-round, freshwater crab-fishing behaviour – primarily among female and infant chimpanzees – living in the rainforest of the Nimba Mountains in Guinea, west Africa.
“The aquatic fauna our ancestors consumed likely provided essential long-chain polyunsaturated fatty acids, required for optimal brain growth and function,” said lead author Kathelijne Koops from the University of Zurich and Kyoto University’s leading graduate programme in primatology and wildlife science.
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Endemic to the far east of Russia, the Amur Leopard has a population of around 84 and is critically endangered. Here follows every species that the WWF lists as critically endangered.
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Endemic to China’s Yangtze River, the Yangtze finless porpoise has an estimated population of 1000-1800
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When discovered in the 1950s, the South China tiger population was estimated to be 4000, by 1996 it was estimated to be only 30-80. Scientists consider the tiger to be “functionally extinct” as one has not been sighted for over 25 years
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Though it is the most populous of all gorilla subspecies, the western lowland gorilla is still critically endangered and its population has declined by 60% in the last quarter century
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6/17 Sumatran Rhinoceros
The Sumatran rhinoceros is the smallest of the surviving rhinoceros species. Only 80 are known to be living today. The last male Sumatran rhino in Malaysia died on 28 May 2019
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There are fewer than 400 Sumatran tigers left today. They are severely threatened by deforestation and poaching
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Half of the rainforest of the Democratic Republic of Congo in which these gorillas live has been destroyed the past 50 years. There were 17,000 Eastern Lowland gorillas in the 1990s but scientists estimate their population has declined by over 50% since then
Getty
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Paula Olson / NOAA
10/17 Javan Rhino
The most threatened of all rhino species, there are only an estimated 58-68 Javan rhino left
Reuters
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The saola was first sighted in 1992, being the first large mammal to be discovered in over 50 years. Scientists have only sighted saola in the wild four times and it is considered critically endangered
12/17 Sumatran Elephant
The Sumatran elephant population now stands at only 2400-2800
Getty
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Getty
14/17 Hawksbill Turtle
The population of the Hawksbill Turtle has declined by more than 80% in the last century. They are threatened by black market poachers who kill them for their shell
Getty
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The population of the black rhino dropped by 98% in the years 1960-1995 due to poaching, it stands today at around 5000
Getty
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The population of the Cross River gorilla has been damaged by deforestation and poaching, it now stands at 200-300
Julie Langford
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The population of the Bornean orangutan has been reduced by over 50% in the past 60 years, now standing at around 104,700. Their habitat has been reduced by at least 50% in the 21st century
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“Further, our findings suggest that aquatic fauna may have been a regular part of hominins’ diets and not just a seasonal fallback food,” she said.
The study began in 2012 when the researchers first saw the chimpanzees fishing for crabs.
For two years, they documented the demographics and behaviour of the group of chimps, while also analysing and comparing the nutritional value of the crabs to other foods in the chimpanzees’ diet.
Crabbing, they learned, not only took place year-round – without regard to season or fruit availability – but intriguingly was negatively correlated with the chimps’ consumption of ants, another diet staple. Mature males were the least likely to consume aquatic fauna.
“Energy and sodium levels in large crabs are comparative with ants,” Dr Koops said, “leading us to hypothesise that crabs may be an important year-round source of protein and salts for females – especially when pregnant or nursing – and for growing juveniles.”
The study sheds light on our own evolution by illustrating that fishing behaviours may not be restricted by habitat as could be assumed.
“This isn’t the first case of non-human primates eating crabs,” said senior co-author Tetsuro Matsuzawa, “but it is the first evidence of apes other than humans doing so.”
He said notable previous observations of primates eating crabs came from “monkey species in locations consistent with aquatic faunivory – lakes, rivers, or coastlines – and not in closed rainforest.”
He added: “It’s exciting to see a behaviour like this that allows us to improve our understanding of what drove our ancestors to diversify their diet.”
