Human bipedalism – walking upright on two legs – may have evolved in trees, and not on the ground as previously thought, according to a new study involving UCL researchers.
根據英國倫敦大學學院，研究人員們參與的一項新研究，人類雙足行走(用兩條腿直立行走)可能曾在樹上進行演化，而不是如先前被認為，在地面上那樣。
In the study, published today in the journal Science Advances, researchers from UCL, the University of Kent, and Duke University, USA, explored the behaviours of wild chimpanzees - our closest living relative - living in the Issa Valley of western Tanzania, within the region of the East African Rift Valley.
在今天(2022年12月14日)發表於《科學進展》期刊的該項研究中，來自英國倫敦大學學院(UCL：University College London)、英國肯特大學及美國杜克大學的研究人員們探索了，生活於坦桑尼亞西部，伊薩河谷之野生黑猩猩(我們最親近的現存親緣動物)的行為。
Known as ‘savanna-mosaic’ – a mix of dry open land with few trees and patches of dense forest - the chimpanzees’ habitat is very similar to that of our earliest human ancestors and was chosen to enable the scientists to explore whether the openness of this type of landscape could have encouraged bipedalism in hominins.
被稱為‘熱帶稀樹草原馬賽克式(樹木稀少之乾燥開闊地區與茂密森林小區域的混合體)之’黑猩猩的棲息地非常類似，咱們最早人類原種的棲息地。因此，被選中來使此些科學家們能探索，這種類型的空曠地貌是否可能曾助長了，於人科動物中的雙足行走。
The study is the first of its kind to explore if savanna-mosaic habitats would account for increased time spent on the ground by the Issa chimpanzees, and compares their behaviour to other studies on their solely forest-dwelling cousins in other parts of Africa.
這是探索熱帶稀樹草原馬賽克式棲息地，是否能說明，由伊薩河谷黑猩猩花增多之時間於地面，並與其他針對其僅棲息於森林中之遠親的研究，比較牠們行為的首度研究。
Overall, the study found that the Issa chimpanzees spent as much time in the trees as other chimpanzees living in dense forests, despite their more open habitat, and were not more terrestrial (land-based) as expected.
總的來說，該項研究發現，伊薩河谷黑猩猩在樹上度過的時間，與生活在茂密森林中的其他黑猩猩一樣多。儘管，它們的棲息地更為開闊，不過並非如預期般，是較為陸棲的(以陸地為主)。
Furthermore, although the researchers expected the Issa chimpanzees to walk upright more in open savanna vegetation, where they cannot easily travel via the tree canopy, more than 85% of occurrences of bipedalism took place in the trees.
此外，雖然研究人員們預期，在伊薩河谷黑猩猩無法輕易經由樹冠行進的開闊稀樹草原植被中，牠們較為直立行走。不過，超過85%的雙足行走發生於樹上。
The authors say that their findings contradict widely accepted theories that suggest that it was an open, dry savanna environment that encouraged our prehistoric human relatives to walk upright – and instead suggests that they may have evolved to walk on two feet to move around the trees.
此些撰文者們表示，他們的研究發現與被廣泛接受之暗示，助長咱們史前人類同族直立行走的理論相矛盾。也就是反而暗示，他們可能曾演化以雙腳在樹上移動。
Study co-author Dr Alex Piel (UCL Anthropology) said: “We naturally assumed that because Issa has fewer trees than typical tropical forests, where most chimpanzees live, we would see individuals more often on the ground than in the trees.
該項研究合撰人，Alex Piel博士(倫敦大學學院人類學)表示：我們自然而然地假設，因為伊薩河谷具有比大多數黑猩猩棲息之典型熱帶森林少的樹木。因此，我們會看到個體於地面上，比在樹上更為頻繁。
Moreover, because so many of the traditional drivers of bipedalism (such as carrying objects or seeing over tall grass, for example) are associated with being on the ground, we thought we’d naturally see more bipedalism here as well. However, this is not what we found.
此外，由於許多傳統的兩足行走驅動因素(譬如，諸如搬運物體或俯瞰高草)皆與是在地面上有所關聯。我們認為，自然也會在這裡，看到更多的雙足行走。不過，這不是我們所發現的。
“Our study suggests that the retreat of forests in the late Miocene-Pliocene era around five million years ago and the more open savanna habitats were in fact not a catalyst for the evolution of bipedalism. Instead, trees probably remained essential to its evolution – with the search for food-producing trees a likely a driver of this trait.”
「我們的研究暗示，大約5百萬年前，中新世到上新世晚期森林的隱退，及更開闊的熱帶稀樹草原棲息地，實際上不是兩足動物演化的一個促進因素。反而，樹木可能仍然對其演化至關重要。因為，尋找生產食物的樹木，可能是此特點的一種驅動因素。」
To establish their findings, the researchers recorded more than 13,700 instantaneous observations of positional behaviour from 13 chimpanzee adults (six females and seven males), including almost 2,850 observations of individual locomotor events (e.g., climbing, walking, hanging, etc.), over the course of the 15-month study.
為了證實他們的研究發現，此些研究人員記錄了，在15個月之研究過程中，13隻成年黑猩猩(6隻雌性及7隻雄性)13700多次的位置行為瞬時觀察結果，包括近2850次個體位移事件(例如，攀爬、行走、懸掛等)的觀察結果。
They then used the relationship between tree/land-based behaviour and vegetation (forest vs woodland) to investigate patterns of association. Similarly, they noted each instance of bipedalism and whether it was associated with being on the ground or in the trees.
之後，他們使用以樹木/陸地為主之行為與植被(也就是森林對林地)之間的關係，來研究關聯模式。同樣地，他們記錄了每一個雙足行走的例子，及是否這與在地面上或於樹上有所關聯。
The authors note that walking on two feet is a defining feature of humans when compared to other great apes, who “knuckle walk”. Yet, despite their study, researchers say why humans alone amongst the apes first began to walk on two feet still remains a mystery.
此些撰文者們特別指出，當與“指關節行走”之其他巨猿(如大猩猩、黑猩猩等類人猿)相較下，用雙腳行走是人類的一個明確特點。然而，儘管他們的研究，研究人員們表示，為何在類人猿中，僅人類最早開始用雙腳行走，仍然是個謎。
Study co-author Dr Fiona Stewart (UCL Anthropology and Liverpool John Moores University) said: “To date, the numerous hypotheses for the evolution of bipedalism share the idea that hominins (human ancestors) came down from the trees and walked upright on the ground, especially in more arid, open habitats that lacked tree cover. Our data do not support that at all.
該項研究合撰人，(倫敦大學學院及利物浦約翰摩爾斯大學人類學)Fiona Stewart博士表示：迄今為止，有關雙足行走演化的眾多假設，共有人科動物(人類的原種)從樹上下來，並在地面上直立行走，特別是在缺乏樹木覆蓋，較乾旱、空曠之棲息地的見解。我們的數據根本不支持那見解。
“Unfortunately, the traditional idea of fewer trees equals more terrestriality (land dwelling) just isn’t borne out with the Issa data. What we need to focus on now is how and why these chimpanzees spend so much time in the trees - and that is what we’ll focus on next on our way to piecing together this complex evolutionary puzzle.”
「不巧的是，傳統觀念認為較少樹木等於較多陸棲之地(陸上棲地)的傳統見解，完全沒有獲得以伊薩河谷之數據的支持。目前，我們所需著重的是，此些黑猩猩如何及為何，在樹上花費如此多的時間。而且，那是我們拼湊此複雜演化謎團之方法，下一步將著重的重點。」
Study lead author Rhianna Drummond-Clarke (University of Kent) said: “Many fossil human relatives have ape-like forelimbs – with long arms, more mobile shoulders and curved fingers – that are useful for swinging and climbing in the trees.
該項研究首要撰文人，Rhianna Drummond-Clarke(肯特大學)宣稱：「許多成化石的人類親緣動物，具有類似類人猿的前肢(長臂、較靈活的肩膀及彎曲的手指)。這對於在樹上擺盪及攀爬很有用。
While some have argued that these ‘tree adaptations’ are remnants from a more ape-like, arboreal past and no longer functionally important, our study suggests that trees remained an important part of their daily lives.”
儘管有些人一直辯稱，此些‘樹適應’是來自一種較像類人猿、棲息樹上之過去的殘存部分，且功能上不再重要。不過，我們的研究暗示，樹仍然是牠們日常生活的重要部分。」
網址：https://www.ucl.ac.uk/news/2022/dec/early-humans-may-have-first-walked-upright-trees
翻譯：許東榮
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