與大多數陸地哺乳動物的狗爬式游姿不同,一對研究員夫婦以錄影的方式發現,猿類的泳姿類似人類的蛙式,為猿類游泳和潛水的行為首次留下動態影像記錄。
約翰尼斯堡金山大學解剖學院Renato Bender博士生和瑞士伯爾尼大學社會和預防醫學研究所Nicole Bender博士合作,探討靈長類和水的互動模式。他們以美國的一隻黑猩猩和一隻紅毛猩猩為研究對象,這些黑猩猩和紅毛猩猩由人類撫養,並曾學習游泳和潛水。為了避免黑猩猩溺水,研究者們在水池最深處的上方拉了兩條繩索。他們指出,黑猩猩Cooper很快就對繩索產生興趣,幾分鐘後便開始潛入兩米深的水池,撿拾池底的物品。
「我們原本以為很怕水的動物,竟然也能潛水。」Renato Bender說。數周後,Cooper開始在水面上游泳。
在南加州一間私人動物園,紅毛猩猩Suryia也被拍下罕見的游泳和潛水行為。Suryia可以自由潛水至12米深。Cooper和Suryia游泳時的腿部動作都很像人類的蛙式,只是Cooper雙腳一起踢,而Suryia是兩腳交換踢。研究人員相信這樣的泳姿可能是遠古時期為了適應樹棲生活演化而來。
大多數的哺乳類都直覺的以類似狗爬式的動作游泳,這樣的動作未經學習便展現出來,而且是跨物種的行為。相反地,人類和猿則必須學習游泳。猿類的樹棲祖先很少在陸地上移動。科學家說,牠們發展出其他跨越小河流的技能,直立涉水或靠自然形成的橋通過河流。牠們失去了游泳的直覺。人類是猿的遠親,也缺少游泳的直覺。但跟猿不同的是,人類喜歡水而且能學習游泳和潛水。
「猿在水中的行為一直是人類學上被忽略的領域。因此儘管學術界對猿的研究相當深入,牠們的游泳行為卻從未經過科學探討。我們也找到其他猿游泳和潛水的紀錄,但只有Cooper和Suryia得以被錄影下來。我們不知道人類的祖先何時開始經常性的游泳和潛水。」Nicole Bender說。
人類和猿類的特殊游泳姿勢可能不是早期適應樹棲生活的結果。動物園多年來都以護城河的方式限制圈養黑猩猩、大猩猩和紅毛猩猩。當猿類嘗試進入深水中,下場都是溺水。有些人認為這是人類和猿的基本差異:人類喜歡水,能夠學會游泳,而猿喜歡待在陸地上。
但研究結果顯示此種差異並非絕對。Benders夫婦在他們的網站上寫道,「我們準備把5隻猿類(4隻黑猩猩和1隻紅毛猩猩)游泳和潛水的能力寫成研究報告。牠們的能力顯示,人類和非人類古猿和水的互動模式可能並非想像中的大。這是學術界首次比較人類和非人類古猿的游泳動作、水下行為、呼吸控制和潛水反應。」
A husband and wife research team has provided the first video-based observation of apes that can swim and dive. Instead of the usual dog-paddle stroke used by most terrestrial mammals, these animals use a kind of breaststroke.
The studies were conducted by Renato Bender, who is working on a PhD in human evolution at the School of Anatomical Sciences at Witwatersrand University in Johannesburg, and Dr. Nicole Bender, who works as an evolutionary physician and epidemiologist at the Institute of Social and Preventive Medicine at the University of Bern in Switzerland.
The researchers’ main focus is primates’ interaction with water. They studied a chimpanzee and an orangutan in the United States. These captive primates were raised and cared for by humans and have learned to swim and to dive.
“We were extremely surprised when the chimp Cooper dived repeatedly into a swimming pool in Missouri and seemed to feel very comfortable,” said Renato Bender.
To prevent the chimp from drowning, the researchers stretched two ropes over the deepest part of the pool. They report that Cooper became immediately interested in the ropes and, after a few minutes, he started diving into the two-meter-deep water to pick up objects on the bottom of the pool.
“It was very surprising behavior for an animal that is thought to be very afraid of water,” said Renato Bender. Some weeks later, Cooper began to swim on the surface of the water.
The orangutan Suryia, who was filmed in a private zoo in South Carolina, also possesses this rare swimming and diving ability. Suryia can swim freely up to 12 meters.
Both animals use a leg movement similar to the human breaststroke frog kick. While Cooper moves the hind legs synchronous, Suryia moves them alternatively.
The researchers believe that this swimming style might be due to an ancient adaptation to an arboreal life.
Most mammals use the so-called dog-paddle, a mode of locomotion that they employ instinctively, which means an unlearned, species-wide behavior.
Humans and apes, on the other hand, must learn to swim. The tree-dwelling ancestors of apes had less opportunity to move on the ground. The scientists say they developed alternative strategies to cross small rivers, wading in an upright position or using natural bridges. They lost the instinct to swim.
Humans, who are closely related to the apes, also do not swim instinctively. But unlike apes, humans are attracted to water and can learn to swim and to dive.
“The behavior of the great apes in water has been largely neglected in anthropology. That’s one of the reasons why swimming in apes was never before scientifically described, although these animals have otherwise been studied very thoroughly. We did find other well-documented cases of swimming and diving apes, but Cooper and Suryia are the only ones we were able to film. We still do not know when the ancestors of humans began to swim and dive regularly,’ said Nicole Bender.
“This issue is becoming more and more the focus of research. There is still much to explore,” said Renato Bender.
The swimming strokes peculiar to humans and apes might be the result of an earlier adaptation to an arboreal life.
For many years, zoos have used water moats to confine chimpanzees, gorillas or orangutans. When apes ventured into deep water, they often drowned. Some argued that this indicated a definitive difference between humans and apes: people enjoy the water and are able to learn to swim, while apes prefer to stay on dry land.
But it turns out that this distinction is not absolute.
On their website, the Benders write, “We are preparing papers with the first descriptions of the swimming and diving abilities of five different individuals (4 common chimpanzees, 1 orangutan) which revise the allegedly fundamental difference between humans and non-human hominoids concerning their interaction with water. For the first time it is possible to compare swimming movements, behavior under water, breath-control and diving response between different non-human hominoids and humans.”
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