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Ötzi the Iceman may have come to an unfortunate end while crossing the Alps more than 5,000 years ago, but thanks to his well-preserved remains, he's still helping us understand our past. A new digital reconstruction of the mummy's ribcage is providing fresh insights into modern human evolution.

Researchers wanted to know if the slender ribcage we see in modern humans is a derived feature unique to our lineage or if it's an older, ancestral trait. To find out if this is the case, José M. López-Rey from the National Museum of Natural Sciences in Madrid, Spain, and colleagues reconstructed the ribcages of four prehistoric Homo sapiens.

In addition to Ötzi, they studied Nazlet Khater 2 (a 30,000-year-old fossil of the oldest human found in Egypt), Ohalo II H2 (a 19,000-year-old human skeleton discovered in Israel) and Dolní Věstonice 13 (30,000-year-old skeleton found in the Czech Republic).

The resulting 3D models were then compared with the ribcages of 59 modern human individuals, along with two Neanderthals and one Homo erectus fossil.

So what did the team find? The fossilized ribcages from early H. sapiens, including those from Nazlet Khater 2, Ohalo II H2 and Dolní Věstonice 13, have characteristic rounded, or globular proportions, typical of modern humans. This consistent shape suggests a shared fundamental thoracic structure within our species. The study is in the journal Communications Biology.

How the climate shaped us

Additionally, the size and specific shape of these ribcages appear to be tied to climate. Individuals living in warmer or more temperate climates, such as those represented by the Nazlet Khater 2 and Ohalo II H2 fossils, tended to have smaller, more cylindrical ribcages. But early humans in colder environments, like Dolní Věstonice 13, possessed larger, broader ones, which could have been an adaptation to their cold surroundings.

Ötzi's ribcage falls somewhere between these two types, which could reflect a need to adapt to seasonal temperature changes as he moved through the alpine region.

One of the most noteworthy aspects of this research is that the Dolní Věstonice 13 ribcage is almost as large as those found in Neanderthals and wider, similar to H. erectus. This challenges the long-standing belief that H. sapiens ribcages were always less robust than those of Neanderthals and H. erectus.

The findings suggest that human body variations are more complex than previously thought. "This research joins others and suggests a great morphological variability in H. sapiens sensu lato (both fossil and recent) that cannot be reduced to a generalized slender Bauplan, as it depends not only on genetics but also on the climatic plasticity of our species," say the authors.

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