First of Our Kind

ホモ属直系の祖先? セディバ猿人の衝撃

By Kate Wong K. ウォン
English 日本語 日本語
Sometime between three million and two million years ago, perhaps on a primeval savanna in Africa, our ancestors became recognizably human. For more than a million years their australopithecine predecessors—Lucy and her kind, who walked upright like us yet still possessed the stubby legs, tree-climbing hands and small brains of their ape forebears—had thrived in and around the continent’s forests and woodlands. But their world was changing. Shifting climate favored the spread of open grasslands, and the early australopithecines gave rise to new lineages. One of these offshoots evolved long legs, toolmaking hands and an enormous brain. This was our genus, Homo , the primate that would rule the planet.  私たちの祖先は300万年前から200万年前のある時に,おそらくアフリカの太古のサバンナでヒトと認識される存在になった。ヒトの祖先である「ルーシー」と彼女の仲間のアウストラロピテクス属は,私たちと同じように直立二足歩行をしていたが,類人猿と同様にずんぐりした脚と木登りに適した手,そして小さな脳を持ち,100万年以上もの間,アフリカ大陸の森林やその周辺で暮らしていた。
For decades paleoanthropologists have combed remote corners of Africa on hand and knee for fossils of Homo ’s earliest representatives, seeking to understand the details of how our genus rose to prominence. Their efforts have brought only modest gains—a jawbone here, a handful of teeth there. Most of the recovered fossils instead belong to either ancestral australopithecines or later members of Homo —creatures too advanced to illuminate the order in which our distinctive traits arose or the selective pressures that fostered their emergence. Specimens older than two million years with multiple skeletal elements preserved that could reveal how the Homo body plan came together eluded discovery. Scientists’ best guess is that the transition occurred in East Africa, where the oldest fossils attributed to Homo have turned up, and that Homo ’s hallmark characteristics allowed it to incorporate more meat into its diet—a rich source of calories in an environment where fruits and nuts had become scarce. But with so little evidence to go on, the origin of our genus has remained as mysterious as ever.  古人類学者はホモ属がどのように誕生したかを明らかにするために,何十年にもわたってアフリカの人里離れた地帯で四つんばいになって最初期のホモ属の化石を探してきた。彼らの努力の成果は,あるところで顎骨が1つ見つかり,別のところで歯が数本見つかるといったくらいのささやかなものだった。収集できた化石のほとんどは祖先のアウストラロピテクス属か,最初期よりも新しい年代のホモ属のものだった。
Lee Berger thinks he has found a big piece of the puzzle. A paleoanthropologist at the University of the Witwatersrand in Johannesburg, South Africa, he recently discovered a trove of fossils that he and his team believe could revolutionize researchers’ understanding of Homo ’s roots.  南アフリカ共和国ヨハネスブルクにあるウィットウォーターズランド大学の古人類学者ベルガー(Lee Berger)は,その謎を解くカギを見つけたと考えている。彼は最近,ホモ属のルーツに関する従来の見解を覆しかねない(と彼と彼のチームが信じる)化石を発見した。