With Wimbledon in full swing and Rafael Nadal looking as fearsome as ever I’ve decided that the middle-class British sporting world and the world of physical anthropology should collide.
I’ve always thought Mr. Nadal looks a bit Neanderthal-y, and it seem as though the internet agrees with me. But would Nadal be as good at tennis if he really were a Neanderthal?
Neanderthals (Homo neanderthalensis) are known for being very strongly built and capable of producing very powerful movements of the arm. So far so good for my Nadal Neanderthal hypothesis. The problem comes when you examine the anatomy of the shoulder joint itself. Movement at the shoulder takes place between the head of the humerus (the bone of your upper arm) and the glenoid fossa which is part of the shoulder blade, or scapula (fig. 1).
The shoulder is a ball and socket joint which means that it has a really high range of motion allowing us to rotate our shoulder in all sorts of directions. In a joint, the surface area of the two bones in contact related to the range of motion at that joint, and the strength of the forces that are transmitted through this joint.
Comparing a Neanderthal and a modern human shoulder shows that the Neanderthal glenoid is taller relative to its width than is expected for a modern human. The Neanderthal glenoid is also narrower relative to the width of the humeral head than is expected for a modern human (Churchill & Trinkaus, 1990).
These differences are the same as those between Neanderthals and our ancestors, the anatomically modern Homo sapiens who were around at the same time, so it’s definitely not a case of modern humans being skinny, weak versions of Neanderthals.
But why? Again, there are two possible reasons: the Neanderthal glenoid is taller than you might expect, or the modern human glenoid is wider than you would expect.
I mentioned above that the surface area of a joint relates to the strength of the forces that are transmitted through it, and it so happens that putting more force through the shoulder joint causes the glenoid to increase its surface area by increasing height. Since the arm bones of Neanderthals are very robustly built, and have incredibly pronounced muscle attachments, it would seem that Neanderthal glenoids are, in fact, just as tall as we would expect.
That leaves us with the option that humans glenoids are wider than they should be. Greater joint surface area can also represent increased range of motion at the joint, and a wider glenoid means a greater front-to-back range of motion at the shoulder joint. Greater range of motion in bringing the shoulder back is particularly useful when bringing the arm back for a throwing motion, and rapid acceleration to bring the arm forward would cause stresses and strains in a front-to-back direction, stimulating bone growth in the same direction, increasing the width of the glenoid fossa.
So it is not just differences in the strength of forces that determines the shape of the glenoid, but also the direction in which these forces are experienced by the joint.
Back to the tennis. Is Nadal a Neanderthal? Well, tennis involves a lot of bringing the arm backward and forward at very high speeds, generating very high forces in a back-to-front direction at the shoulder, which should mean that Nadal’s glenoid fossa is even wider than the average modern humans, and nothing like that of a Neanderthal at all.
But, well spotted – early Homo sapiens probably weren’t playing tennis. So what caused the difference between Neanderthal shoulders and anatomically modern humans shoulders?
It seems that Neanderthals were quite keen on close-quarters combat with the large animals they hunted for meat, with fossils showing that they sustained injuries with a very similar pattern to modern rodeo riders. this could also help explain why Neanderthals had such strong arm and shoulder muscles, and were adapted to sustain high forces at the shoulder.Meanwhile our ancestors, the anatomically modern humans and those who came before them probably preferred to hunt from a distance, with the earliest spears being dated at 400, 000 years old (Thieme, 1997).
More recently, Adam Benton over at EvoAnth has written a great piece about when the ability to throw is likely to have evolved in the human lineage although, as he makes clear, really proving it is far from easy!
Churchill, S., & Trinkaus, E. (1990). Neandertal scapular glenoid morphology. American Journal of Physical Anthropology, 160, 147–160.
Thieme, H. (1997). Lower Palaeolithic hunting spears from Germany, 385, 807–810.