Why does the human body look the way it is? While I suppose it could have magically appeared in its present form ex nihilo, it is more likely to have evolved from existing structures to adapt to the surrounding environment. Why am I thinking about this? Because I’m reading the fascinating Story of the Human Body by Daniel Lieberman, a professor of human evolutionary biology.
The forerunners of the Homo genus show up in the fossil record some 6-7 million years ago. Then between 2-4 million years ago we have a bunch of Austropithecus fossils, of which Lucy is the most famous. Then comes Homo habilis somewhere around the 2 million year-old mark followed by its cousins. The last of these, Homo sapiens, shows up 0.2 million years ago thereabouts. The boardgame Origins How We Became Human begins somewhere in this time-frame leading up to modern day technological and polluting humankind, and you one can spend many hours simulating all of this in a fun yet challenging game.
Homo shows up as an ice age is beginning. Food is getting sparse. The climate is getting colder. While our close cousins, the chimpanzees, are still well-adapted to life in the trees and eating fruit, even they have to chew on bark and other plants in lean times. Homo starts to find a different niche. We are one of the few animals that spend much of our waking hours in the upright position, on two legs. And before comfy sofas, we walked a lot more. The savannas and grasslands require more walking and less swinging through the trees. Freeing our hands allows us to create better tools, whether it be digging for tubers or getting energy-and-nutrient-rich meat. It’s all about food. Eat or die. And most animals spend most of their lives looking for food and eating it.
We’re not as fast or as fierce as lions. We don’t have the speed to bring down a running antelope and rip its flesh with powerful jaws and teeth. But a group of us can run down an antelope eventually. We are one of the best long-distance runners in the animal kingdom, with thin hairs and sweat glands that allow us to keep going without overheating. And we have our hands free while doing it. Lieberman covers the wide range of anatomical adaptations from head to toe that allows us to do this. From the way our head sits and bobs around on our neck to the arch in our foot and the size of our big toe, we are long-distance running machines.
I didn’t realize how much you can learn from fossil teeth. Lieberman goes through this in detail while keeping the reader engaged, which is no mean feat. And he does calorie counts to estimate how much our forebears might have to forage or hunt to stay alive. Processing our food to make it more efficiently digestible – by pounding, chopping, cooking – also led to adaptations in why our jaws and teeth are different from our chimp relatives. You can see the process of change through the fossil record from the various Austropithecus through the Homo hominids. And to have efficient energy stores, we need fat. We are fatter than most, even in the distant past, not to mention today – where our bodies still crave the fat and we get so much less exercise driving our cars to the supermarket and foraging in the aisles of abundance.
To get the meat, it is more efficient to hunt in groups. And men do this best since they don’t have to physically nurse children. But to communicate and coordinate and thrive as a social community, we need to expand our skill set beyond our dexterous hands. That requires growing our brain – an efficient prediction machine that helps us size up our immediate situation and act accordingly. I learned that our guts are about equal in relative weight to our brain, unlike our chimp relatives with much smaller relative brains. Our brain is energy-hungry and we have to keep it well fed. To do so, we store fat that we metabolize into glucose to keep the energy supply constant and reliable.
All this makes me think about my origin-of-life research and protometabolic systems. What do living systems need? Food to stay alive. And with a little more excess, organisms can grow and reproduce. Humans are particularly adept at accumulating more energy than we need for our daily sustenance, especially once better tools and hunting weapons, not to mention cooking, became part of our daily routine. Better to save up for those cold, icy days. Except for photosynthetic organisms that can transform carbon dioxide from the atmosphere, the rest of us have to get our carbon building blocks from other sources: plants, animals, fungi, and other organisms dead or alive. To survive and thrive, a metabolism needs to be efficient and the food gathering needs to improve. I need to think about this at a chemical level. It’s hard for me to imagine, but I can make analogies to what larger organisms do in their quest for food and nutrition. Ultimately it all comes down to grabbing energy to stay alive.
P.S. I also did not appreciate how good humans are at throwing objects with precision. Our arms, shoulders, hand-eye coordination, all kept in balance, are amazing!
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