Our big brains require a lot of energy to fuel. Which means they need a lot of food. And that would require an awful lot of chewing. Except our ancestors' jaws have been getting weaker over time.
This paradox has puzzled palaeoanthropologists. A few million years ago our family had massive jaws. But as our brains got bigger they whithered away. The opposite of what you'd expect.
Potential explanations for this paradox have included them using fire to make food easier to chew or switching to softer foods. Yet nobody has quantified whether these would be enough.
Until now! A group of researchers have pinpointed various tricks our ancestors could have employed to make chewing easier. This would have allowed them to invest all the energy they spent chewing (and growing powerful chewing muscles) on other important things. Like maybe growing a big brain.
A history of jaws
The jaws of chimps (and presumably our most recent common ancestor with them) are pretty impressive. But over the course of human evolution we developed an even better set of knosshers.
Around 4 million years ago the our ancestors had evolved into Australopithecus. This group of hominins were quite ape-like; spending a lot of time in the trees and having small brains. But they differed in a few key areas. Like walking upright on the ground.
Another key difference was in their mouth. Their chewing teeth grew to massive sizes and their muscles enlarged to match. As an interesting aside, the canines got a lot smaller. These are teeth chimps use for fighting each other. Their absence on Australopithecus suggests they may have had a much more peaceful home life.
This massive chewing capability grew to the extreme in Paranthropus. This offshoot of Australopithecus rearranged most of their face to accommodate even larger chewing muscles and teeth. This was so prominent that when they were first discovered they earned the nickname " nutcracker man ".
It turns out they might not have actually cracked nuts. Instead, it seems that these powerful teeth were actually built for endurance. Their powerful muscles could just keep going and going, all day long. As such they were able to eat high volumes of low quality food. Like maybe grasses and other stuff we can't survive on. However, this adavantage doesn't seem to have helped them in the long run, and Paranthropus ultimately went extinct.
Instead evolution led to the emergence of our genus - Homo. Starting with Homo erectus our ancestors' jaws got smaller and smaller. As did the teeth in them. Now we have one of the more pathetic set of jaws found in the ape family.
Fussy eaters
What makes the history of our jaw unusual is it follows the opposite trend you'd expect. During the evolution of Homo erectus our brain got bigger, increasing the demand for food and thus chewing.
Yet their jaws actually got smaller over this period. Now modern humans have some of the smallest teeth of any member of our family, yet some one of the most food-demanding brains. Many explanations for this apparent contradiction had been proposed, yet none really seemed sufficient. For example, it was thought that by using fire Homo erectus could have broken down the food before chewing; lessening the demands on their jaw. However, reliable evidence of fire comes well after big brains and weak jaws developed.
Alternatively they could have switched to softer foods, such as meat. However, the large hominin teeth seen earlier in our evolution weren't very good at slicing through meat. As such the benefits to chewing would have been relatively minimal. As such, if 1/3 of a hominins' diet was meat they would only be chewing 13% less.
Food for thought
Research has identified just how our ancestors could have met the energy demands from their brains without chewing much.
They stuck all sorts of equipment on people as they ate to measure just how much energy it took to chew various food with our pathetic little jaws. Much to nobodies surprise, this revealed that the old hominin diet of roots and tubers - which is what Australopithecus probably ate - was pretty tough. Hence why they evolution resulted in them having such hefty chewing capabilities.
After a few experiments, they found ways in which Homo erectus could have reduced this chewing cost whilst still keeping their growing brain fuelled. Fire would be one strategy. Cooking food softened it up, reducing chewing costs. However - as previously mentioned - the evidence early Homo erectus used fire is circumstantial. Meat, being softer, could also have reduced the amount of chewing needed to a degree. But again, not by that much.
They found that the real secret (which is plausible based on the technology we know Homo erectus had) was to eat a lot of meat and cut it up. Slicing meat reduced the amount of force needed to chew by 1/4. Additionally, after cut meat had been chewed it was much smaller than regular slabs of chewed meat. This would have increased the ease with which our ancestors could have digested it.
And we know that they were cutting up their meat. Many of the early stone tools associated with Homo erectus have microwear traces of being used to slice up flesh. This wouldn't just make it more convinent, but offer a three-fold evolutionary benefit:
- Reducing the energy needed to chew the food
- Reducing the energy needed to digest the food
- Reducing the energy needed to grow powerful (yet now useless) chewing muscles
It turns out cutlery might be one of the key secrets to our success.
tl;dr
Human ancestors cut up their food to reduce the amount of energy they had to spend chewing it and increasing the energy they got out of it. This could have helped fuel their big brains.
References
Boyd, R. and Silk, J.B., 2015. How Humans Evolved. WW Norton & Company, New York..
Zink, K.D. and Lieberman, D.E., 2016. Impact of meat and Lower Palaeolithic food processing techniques on chewing in humans. Nature.
