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Scientists say ancient footprints left in wet dirt on a Kenyan lakeside suggest that two early human ancestors were neighbors about 1.5 million years ago.
科学家说，肯尼亚湖边湿土中留下的古代脚印表明，大约150万年前，有两个早期人类祖先是邻居。
Two separate species made the sets of footprints “within a matter of hours, or at most days,” said paleontologist Louise Leakey, a writer of the research published recently in the journal Science.
最近发表在《科学》杂志上的这项研究的作者之一、古生物学家路易丝·利基说，这两个不同的物种“在几个小时内，或者最多几天内”就形成了这组脚印。
Paleontologists study fossils to learn about the history of life on Earth.
古生物学家研究化石是为了了解地球上的生命历史。
Scientists already knew from earlier fossil finds that these two extinct lines of human development – called Homo erectus and Paranthropus boisei – lived about the same time in the Turkana Basin.
科学家们已经从早期的化石发现中了解到，这两条已经灭绝的人类发展线--直立人和鲍氏傍人--大约在同一时间生活在图尔卡纳的盆地上。
But dating fossils is not exact.
但化石年代的测定并不准确。
“It’s plus or minus a few thousand years,” said paleontologist William Harcourt-Smith of Lehman College and the American Museum of Natural History in New York.
雷曼学院和纽约美国自然历史博物馆的古生物学家威廉·哈考特-史密斯说：“它可能会多算或少算几千年的时间。”
He was not involved in the study.
他没有参与这项研究。
Yet with fossil footprints, “there’s an actual moment in time preserved,” he said. “It’s an amazing discovery.”
不过，有了化石足迹，“它保存下了真实的某一刻，”他说。“这个发现很了不起。”
Researchers found the fossil footprints in 2021 in what is today Koobi Fora, Kenya, said Leaky, who is based at Stony Brook University in New York.
纽约石溪大学的Leaky说，研究人员于2021年在如今的肯尼亚Koobi Fora发现了这些化石足迹。
Study co-writer Kevin Hatala is a paleoanthropologist at Chatham University in Pittsburgh, Pennsylvania.
该研究的合著者凯文·哈塔拉是宾夕法尼亚州匹兹堡查塔姆大学的古人类学家。
He said the two species likely knew of each other’s existence whether they left the prints at the same time or a day or two apart.
他说，这两个物种很可能知道对方的存在，无论他们是在同一时间留下指纹，还是相隔了一两天。
“They probably saw each other, probably knew each other was there and probably influenced each other in some way,” Hatala said.
哈塔拉说：“他们可能看到了对方，可能知道对方生活在那里，也可能在某种程度上影响了对方。”
Scientists were able to tell the difference between the two species because of the shape of the footprints.
根据脚印的形状，科学家们能够分辨出这两个物种之间的区别。
The shape of each informed researchers about the structure of the foot and how it was being used at the time.
每只脚的形状都可以让研究人员了解他们脚的结构以及当时的使用方式。
Homo erectus appeared to be walking similarly to how modern humans walk – striking the ground heel first, then moving weight over the ball of the foot and toes and pushing off again.
直立人的行走方式似乎与现代人的行走方式相似--脚跟先着地，然后将重心移到前脚掌和脚趾上，然后再向前走。
The other species, which was also walking upright, was moving “in a different way from anything else we’ve seen before, anywhere else,” said co-writer Erin Marie Williams-Hatala, a human development anatomist at Chatham.
另一个物种也是直立行走的，他的移动方式与我们以前见过的任何其他物种都不同，查塔姆大学的人体发育解剖学家、合著者埃琳·玛丽·威廉姆斯-哈塔拉说。
Among other details, the footprints suggest greater ability of movement in their big toe, compared to Homo erectus or modern humans, said Hatala.
哈塔拉说，还有其他细节表明，与直立人或现代人相比，他们的大脚趾具有更强的运动能力。
Our common primate ancestors probably had hands and feet fit for grasping branches.
我们共同的灵长类祖先的手和脚可能比较适合抓握树枝。
But, over time, the feet of human ancestors developed to permit walking upright, researchers say.
但是，研究人员说，随着时间的推移，人类祖先的脚发展成了可以直立行走。
The new study adds to a growing amount of research that suggests the change to walking on two feet did not happen at a single moment, in a single way.
在越来越多的研究中，这项新研究又是一个补充，说明人类用两只脚走路这个改变发生的时间和方式都不同。
Instead, there may have been a number of ways that early humans learned to walk, run and slide on prehistoric muddy hills.
相反，早期人类在史前泥泞的山丘上学会行走、跑步和滑行的方式可能有很多种。
“It turns out, there are different gait mechanics – different ways of being bipedal,” said Harcourt-Smith.
哈考特-史密斯说：“事实证明，有不同的步态机制--两足动物有不同的行走方式。”
I’m Caty Weaver.
我是凯蒂·韦弗。
