人類の北米定住は２万３０００年前？　足跡発見、通説覆す

【ロサンゼルスＡＦＰ＝時事】米国で２万３０００年前の人類の足跡が見つかったとする研究論文が２３日、米科学誌サイエンスに発表された。人類の北米定住は１万６０００年前とされているが、それを大幅に遡る可能性があることを示唆するものだ。（写真は資料写真）
　足跡は、ニューメキシコ州の砂漠にあるかつて湖のほとりだった場所で見つかった。泥に残された足跡が堆積物で埋まり石化したことで保存された。
　論文によると「多くの足跡は１０代を中心とする子どものものと思われ、成人の大きな足跡は子どものものほど見られない」。
　これを説明する仮説として、大人が技術が必要な仕事を担当し、子どもが「運搬」を担当する分業が行われていたことが考えられる。「１０代の子どもに年下の子どもたちが同行していたため、多くの足跡がまとまった形で残った」とする説だ。
　研究チームは、人類がこの湖を訪れたのとほぼ同時期に生息していたと思われるマンモスや古代オオカミ、オオナマケモノの足跡も発見した。
　人類が米大陸に定住した時期は、地球上に氷床が最も広く存在していた「最終氷期極大期」が終わった後とする見方が一般的だ。極大期には北米の大部分が氷に覆われ、アジアからの人類の移動が非常に困難だったと考えられているため、今回の発見は一石を投じるものだ。【翻訳編集ＡＦＰＢＢＮｅｗｓ】

〔ＡＦＰ＝時事〕（2021/09/28-10:35）

Footprints dating back 23,000 years have been discovered in the United States, suggesting humans settled North America long before the end of the last Ice Age, research published Thursday showed.
The findings push back the date at which the continent was colonized by its first inhabitants by thousands of years.
The footprints were left in mud on the banks of a long-since dried up lake, which is now part of a New Mexico desert.
Sediment filled the indentations and hardened into rock, protecting evidence of our ancient relatives, and giving scientists a detailed insight into their lives.
Many tracks appear to be those of teenagers and children; large adult footprints are less frequent, write the authors of the study published in the American journal Science.
One hypothesis for this is the division of labor, in which adults are involved in skilled tasks whereas 'fetching and carrying' are delegated to teenagers.
Children accompany the teenagers, and collectively they leave a higher number of footprints.
Researchers also found tracks left by mammoths, prehistoric wolves, and even giant sloths, which appear to have been around at the same time as the humans visited the lake.
The Americas were the last continent to be reached by humanity.
For decades, the most commonly accepted theory has been that settlers came to North America from eastern Siberia across a land bridge -- the present-day Bering Strait.
From Alaska, they headed south to kinder climes.
Archaeological evidence, including spearheads used to kill mammoths, has long suggested a 13,500-year-old settlement associated with so-called Clovis culture -- named after a town in New Mexico.
This was considered the continent's first civilization, and the forerunner of groups that became known as Native Americans.
However, the notion of Clovis culture has been challenged over the past 20 years, with new discoveries that have pushed back the age of the first settlements.
Generally, even this pushed-back estimate of the age of the first settlements had not been more than 16,000 years, after the end of the so-called last glacial maximum -- the period when ice sheets were at their most widespread.
This episode, which lasted until about 20,000 years ago, is crucial because it is believed that with ice covering much of the northern parts of the continent, human migration from Asia into North America and beyond would have been very difficult.