Although it may seem like we are definitely the winners in the race for survival, we can also claim to be the runners-up. Why? Because as I explained last week, humans are better adapted for efficient fast running than Neanderthals were. Now, I’m definitely not suggesting that this is the reason that we’re still here and Neanderthals died out 30 thousand years ago, but it does seem as if the ability to run quickly over very long distances may explain the shapes of our bodies now. Not to mention some people’s willingness to run marathons and Iron Man races and all sorts of other horrible things.
Mo Farah. He’s not a patch on some people, not to mention early humans. Credit: itv.com.
A true race for life
Endurance running may not just be for ‘fun’ as some people like to call it. I seem to remember watching a documentary once that spoke about Australian Aborigines running kangaroos into the ground over a distance of 50 miles, then killing them for meat. It is also possible that such persistence hunting was used by late Homo erectus and early Homo sapiens to add meat to their diet before projectile weapons were invented.
So how does persistence hunting work?
This week sees the FINAL UPDATE in the Long-Standing Debate series – congratulations on sticking around for a whole 6 million years of evolution!
Carrying on from last week, the only aspect of our bipedalism left to discuss is whether there are any fossil features which reliably indicate whether the owner of the bones was a distance runner in real life.
I’ve already discussed the angle of the glenoid of the scapula in terms of function and in the archaic and the transitional hominins. In Homo erectus and our own species H. sapiens the glenoid faces laterally (sideways) rather than being tilted superiorly (upward). This makes it much harder for us to hold our arms above our heads for long periods of time, or to generate powerful movements while doing so. A large contributing factor to this difference may be down to the fact that we lack a shoulder muscle when compared to chimpanzees (fig. 1).
Figure 1. Humans lack the atlantoclavicularis muscle which runs from the first vertebra (atlas) to the collarbone (clavicle). a, c – front and back views of a modern humans showing muscle groups important in running; b,d, front and back views of a chimpanzee showing the same muscles; e, front view of H. erectus, f front view of Au. afarensis. Credit: cited in Bramble & Lieberman, 2004.
Following on from last week’s installment about the pelvis, I’m going to take a look at the adaptations of the thigh bone (femur) to upright walking.
One of the most important requirements of being able to walk efficiently is keeping your body’s centre of mass (CoM) above your base of support (essentially the size of the area of ground your feet enclose when standing; fig. 1). This is especially important in upright walking since the base of support is so much smaller than for a quadrupedal animal.
Figure 1. Showing the relationship between centre of mass and base of support in a knuckle-walking chimp and an upright human.
You may have seen my tweet/facebook status quoting Henry Gee (Wikipedia), editor of the journal Nature:
“Crushing clams with cartilaginous jaws is like trying to fell a tree with a sock full of custard.”
That was a bit of an exaggeration on Mr. Gee’s part, but the point still stands – how do certain rays (shark relatives with skeletons made of cartilage instead of bone) manage to crack the shells of shellfish in order to eat them? This cartilage is the same soft material that your ear and the end of your nose are made from.