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This 3.3-Million-Year-Old Hominin Toddler Was Kind of Like Us

Analysis of the ancient spine reveals tantalizing similarities—and questions about human evolution

This spine is the earliest intact reference for how humans' skeletons may have developed. (Zeray Alemseged, University of Chicago )
smithsonian.com

The life of Lucy and other Australopithecus afarensis couldn’t be more different than that of their modern relatives. Unlike us, the ancient hominins had brains the size of chimps and hung out in trees to escape predators. But it turns out that they had some important similarities to humans, reports Stephanie Pappas for LiveScience, and a long-dead toddler’s skeleton shows why.

In a study published in the journal PNAS, researchers reveal that the skeleton of a 2.5-year-old nicknamed “Selam,” (“peace” in Amharic) bears some striking similarities to those of her human relatives. Selam lived some 3.3 million years ago, and she was discovered in 2000 just a few miles south of where Lucy—the world-famous Australopithecus afarensis who changed the way modern humans thought about their long-gone ancestors—was discovered decades earlier.

Researchers have already studied Selam extensively. In 2012, they discovered that, like Lucy, she likely climbed trees. But the new study, reports Pappas, is the first time her spine has been examined. That’s a big deal, because vertebrae are often lost overtime time in fossils.

As a result, researchers can’t be exactly sure how many ancient hominins had—or whether their spines were more like modern African apes, which have 13 thoracic vertebrae, or humans, which have 12.

With the help of high-res imaging, scientists studied Selam’s spine in depth for the first time. It turns out that she had lots of vertebrae—seven cervical (neck) and 12 thoracic, to be exact.

A lot like humans, right? Well, kind of. Though the number of thoracic vertebrae matched that of modern humans, Selam’s spinal column showed a major difference in the place where humans’ upper spines transition into the lower back. There, Selam’s spine looked a lot more like other early hominins like Homo erectus. All four of the other early hominins that scientists have studied so far have similar-but-different patterns at that portion of the spine, researchers write.

Since Selam’s spine is intact, it’s the first time scientists have been able to confirm anything about the spinal structure of an early hominin. “This type of preservation is unprecedented, particularly in a young individual whose vertebrae are not yet fully fused,” said Zeresenay Alemseged, who discovered Selam, in a press release.

But it also points to some big unanswered questions, like how hominins like Selam became fully bipedal and eventually evolved into a more modern skeletal structure. When hominins began to walk upright, they became different from all other species—and understanding how may reveal tantalizing truths about the environmental and physical conditions that early humans faced long ago.

It will take even more discoveries to paint a more complete picture of how humans’ early ancestors evolved—but with every new analysis, science slowly chips away at that mystery.

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