Neanderthals were our closest living relatives. At least, until they went extinct. However, despite being so closely related to humans there were still some differences between us.
New research reveals some of these differences might have evolved to help them cope with their unique, meat-heavy diet. In fact, these adaptations could have shaped their whole body.
In particular, their torso has a rather notable triangular shape produced by broad hips. This extra space would have allowed their gut to get bigger and better deal with their meat-heavy diet.
Neanderthal differences
For 150,000 years at least two species of hominin lived on earth. Humans and the Neanderthals. We were very similar (in fact we were so closely related we could interbreed) yet one species went extinct.
No prizes for guessing which.
To try and explain why we managed to survive but the Neanderthals didn't scientists have examined every little bit of our bodies. And they've found many differences between us. Although most don't seem to help explain why the Neanderthals went extinct. Like the fact their teeth often had a different number of roots than ours.
Others do seem fairly substantial. Our brains were taller than theirs, whilst theirs' were longer. The resulting differences in the relative sizes of the various bits and bobs of the brain gave us a cognitive edge. It might have also made the Neanderthals better at smelling than us.
One of the more dramatic differences between us was in the shape of our bodies. We have a barrel-shaped torso that's pretty much the same width the whole way down. This style of body first evolved in Homo erectus around 1.5 million years ago (although there's hints of it earlier in Australopithecus sediba) and was inherited by all successive species. Except the Neanderthals.
They evolved what's sometimes called a "bell shaped" torso. It's relatively normal at the top, but gets larger towards the bottom. This is caused by changes to the shape of the ribcage and wider hips.
Why did the Neanderthals evolve this unique body plan? And is it as significant a difference as it looks?
Gut feeling
Neanderthals had a tough time. They lived through several glacial periods (or ice ages) which would have resulted in harsh winters.
One of the big issues with this sort of environment isn't the cold but the lack of food. Plants become a lot rarer and many animals migrate away. Neanderthals had a varied diet that included birds, fish, plants, and animals. But in these circumstances their choices would have been limited.
To make matters worse, even if they did manage to catch a mammoth in the depths of winter they would be suffering from the same problems. Their food sources were also restricted, so they probably had a lot less fat on their bones. Which sucks because fat is a great food source, being very calorie dense.
Now, the mammoth would still have plenty of calories in it. Except they would be in the form of muscles and other bits. But that wouldn't solve the problem for Neanderthals. These were protein rich food sources and we're limited in the amount of protein we can digest. Our liver and kidneys needs to process it and remove some of the toxic by-products.
So Neanderthals really needed a better gut. One that could deal with more of these toxic products of protein digestion. A larger liver and kidney would do the trick. But that would require a larger torso to store them.
Hence their bell-shaped thorax.
Going on a diet
All of this does make sense, and the estimates for protein consumption limits make this seem reasonable. However, at the end of they day they are still estimates. Estimates that might be based on somewhat shaky foundations
In particular, they infer that Neanderthals would have had to rely on the high-protein meat because of a lack of other food sources. In fact, their estimates are actually predicated on the fact the Neanderthals couldn't have gotten carbohydrates from plants during the winter. This is wrong. Roots and tubers would have provided a handy source of nutrition even during the darkest winter of the glacial periods. The authors try and dismiss this fact by pointing out humans can't digest such plants that well. Unless you cook them first. And Neanderthals cooked their plants too.
Of course, this doesn't mean the hypothesis itself is wrong. It would be interesting to see if Neanderthals still needed a bigger liver even after you took into account the extra calories they could have gotten from plants.
In the mean time this isn't quite enough to show that our different torsos was evolutionary significant. But maybe it does mean our ancestors laughed at the Neanderthals for having a pot belly.
tl;dr
Neanderthals have an oddly shaped torso. This could be explained as an adaptation to a meat heavy diet. I'm not convinced (yet).
References
Ben‐Dor, M., Gopher, A. and Barkai, R., 2016. Neandertals' large lower thorax may represent adaptation to high protein diet. American journal of physical anthropology.
Hardy, B.L., 2010. Climatic variability and plant food distribution in Pleistocene Europe: Implications for Neanderthal diet and subsistence. Quaternary Science Reviews, 29(5), pp.662-679.
