Nature：人与大猩猩进化分歧提前200万年
生物谷报道：日本东京大学博物馆的Gen Suwa的研究小组在埃塞俄比亚发现了距今大约1000万年前的大猩猩的牙齿化石，从而可能将人类与大猩猩的进化分歧时间提前至少200万年。这种大猩猩命名为Chororapithecus abyssinicus。这项新发现公布在8月23日的《自然》杂志上。
日本的这个研究小组在距离埃塞俄比亚首都亚的斯亚贝巴约170公里的沙漠灌木林地区发现了9颗古大猩猩牙齿化石——8颗臼齿和一颗犬齿。研究人员推测这些牙齿至少来源于三个以上的个体。
研究人员通过比较研究发现，这些牙齿在尺寸、各部分比例以及内部结构扫描结果上与现代大猩猩亚种的牙齿均没有明显差别。研究小组得出结论认为，大猩猩与人类进化分歧的时间不应该是早先认为的800万年前，而应该是比1000万年或1100万年前更早一些。而且，在功能上，这些牙齿似乎正在进化。
这一发现具有重大的意义，它将帮助填补化石证据上的巨大空白，并将人类与大猩猩的进化分歧时间向前提前了至少200万年。另外，它将促使人类学家和遗传学家重新确定原始人类与黑猩猩的进化分歧时间。
Suwa教授还表示，本次发现的牙齿化石再一次表明了非洲才是人类与现代非洲猿类的共同起源地，而不是一些人认为的欧亚大陆。
不过，也有科学家对此次结果表示怀疑。美国伊利诺斯大学研究灵长类动物牙齿的古人类学家Jay Kelley表示，他并不确信这些牙齿的主人是大猩猩。还需要更多的化石证据、分析以及讨论等来确定此次发现的新种是否原始人类的祖先。眼下为了谨慎起见，他并不会轻易使用该新种标本来重排原始人类与大猩猩以及黑猩猩的进化分歧时间。
2003年秋天，美国亚特兰大“耶基斯国家灵长类动物研究中心”的萨拉-布洛斯南和弗兰斯德瓦尔发现，僧帽猴不愿意服从它们认为对自己不公平的待遇。两人在试验中发现，一只猩猩在得到自己期望得到的一粒葡萄或者不太期望得到的一根黄瓜后，都会看看同伴得到的是什么东西。那些从出生后一直生活在一起的猩猩，即使得到不太想要的黄瓜一般也不会做出负面反应人，但刚认识不久的猩猩通常会有比较强烈的反应。而且，共同生活时间不长的猩猩，如果和同伴干了一件同样的工作，但是得到的奖赏却没有同伴好，它一般不愿意再去做这件工作。布洛斯南认为：“人类所做的决定趋向于情感化，往往因为对象的不同而变化。”而在这一点上，猩猩和人类相似。
原始出处:
Nature 448, 921-924 (23 August 2007) | doi:10.1038/nature06113; Received 18 June 2007; Accepted 25 July 2007
A new species of great ape from the late Miocene epoch in Ethiopia
Gen Suwa1, Reiko T. Kono2, Shigehiro Katoh3, Berhane Asfaw4 & Yonas Beyene5
- The University Museum, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Department of Anthropology, National Museum of Nature and Science, Hyakunincho, Shinjuku-ku, Tokyo 169-0073, Japan
- Division of Natural History, Hyogo Museum of Nature and Human Activities, Sanda, Hyogo 669-1546, Japan
- Rift Valley Research Service, P.O. Box 5717, Addis Ababa, Ethiopia
- Department of Archaeology and Paleontology, Authority for Research and Conservation of Cultural Heritage, Ministry of Culture and TourismP.O. Box 13247, Addis Ababa, Ethiopia
Correspondence to: Gen Suwa1 Correspondence and requests for materials should be addressed to G.S. (Email: suwa@um.u-tokyo.ac.jp).
With the discovery of Ardipithecus, Orrorin and Sahelanthropus1, 2, 3, 4, 5, 6, 7, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus8, 9 has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12–7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date—5–6 Myr ago and 6–8 Myr ago for the human–chimp and human–gorilla splits, respectively10, 11, 12, 13, 14—and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade15, 16. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10–10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel–dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel–dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10–11 Myr ago.
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