By Stephen Munro, School of Anthropology and Archaeology
Earlier this month, Nature announced the oldest-known engraving from Java, a discovery that has the potential to change the way we think about human evolution. It was surprising because it was so old and from Java, not Africa or Europe, but the most significant element of this discovery may be that the engraver was Homo erectus, and the canvas was a shell.
The dominant paradigm in human evolution has long been that humans became human because they left the forests and became open habitat dwellers (the savanna theory). The story goes that on the savanna, humans learnt to hunt large mammals, and thus transitioned from a plant-based diet to one including more protein. The endurance-running model, where Homo erectus literally runs large mammals to exhaustion, is just one example of this savanna paradigm.
An alternative model, that humans first got a taste for protein from shellfish rather than large mammals, has received relatively little attention, despite appearing to have much stronger explanatory potential.
The scenario goes like this: Imagine a population of apes, living in a forest, plucking fruit from trees. Now imagine these same apes living in a forest where the bases of the trees are regularly inundated by water, so that mussels and oysters grow on the trunks and roots. Now imagine these apes plucking these mussels or oysters off the trees at low tide, and opening them in order to eat them.
Next, imagine these apes learning to dip their heads under the water to look for mussels below the water's surface while wading bipedally, and then imagine them learning to collect mussels by actively diving for them.
This scenario of course would play out over millions of years, but each step is a relatively small one, and since other primates pluck and open oysters (capuchins) and dive for food (macaques) it is well within the realms of biological possibility.
Imagine this population developing a more linear body to move efficiently through the water, better tool using abilities to open mussels, an external nose with downward pointing nostrils to stop water entering the airways, and less fur and more fat under the skin.
Now consider that shellfish can be eaten raw (think of an oyster), and that they don't run or swim away, so that pregnant and nursing women, and children are equally capable of gathering this food resource for themselves rather than relying on men.
Shellfish also contain good levels of omega-3 fatty acids, which are excellent for brain growth.
If our ancestors began diving for shellfish, even in relatively shallow waters, then the evolution of voluntary breath control might follow, which is a basic pre-requisite for human speech.
So there are very good reasons why part-time shellfish gathering may have been an important element in the evolution of humans and the transition from a plant to protein-based diet.
One little shell might help explain our external nose, bipedalism, linear build, tool use, nakedness, extra fat, large brain and even our ability to speak.