The Evolution of Man
(Published in the newspaper Amigoe on the 15th of January 2025)
The last article talked about how dinosaurs went extinct and how mammals came to be. Guess what? Humans and apes are both mammals! We share a common ancestor.
Meet the modern man!
About six to eight million years ago, our ancestors split from the chimpanzee line in Africa. Chimpanzees have a brain size of around 500 cm3, while modern humans have a brain size of about 1,400 cm3. That’s a whopping three times bigger!
Fossils have given us a pretty good idea of how modern humans evolved. It all started with Australopithecus, then Homo habilis, Homo erectus, and finally Homo heidelbergensis.
The Australopithecus, or the southern monkey, had more human traits than the great ape. He walked upright and had teeth that looked more like humans than great apes. The Homo habilis, or the handy man, was around 4 feet tall and had a brain size between 550 and 700 cubic centimeters. He also used tools. The Homo erectus, or the upright man, had a brain size between 625 and 1100 cubic centimeters. He was about 6 feet tall and an excellent runner. His arms were shorter than those of Homo habilis and his legs were longer. The Homo heidelbergensis, named after a city in Germany, was quite similar to modern humans. He had a brain capacity of about 1,200 cubic centimeters. He already controlled the use of fire.
The above is a very summary overview of human development. However, there is a lot of discussion about this. The number of fossils is very small. It is also not a straight-line development. So it is not the case that one stage neatly followed the other stage. Many intermediate forms have existed simultaneously and some lines of development went extinct.
People often use brain content as a way to measure how smart someone is. But it’s actually more important how the brain is structured and how it works. Most of the brain’s activity happens in the cerebral cortex, which is the outer layer of the brain near the connections between brain cells called synapses. Synapses are like little bridges that allow brain cells to talk to each other. They need a lot of energy to work, and that energy comes from the blood. The blood gets to the brain through the cerebral artery, which enters the brain through a tiny hole in the skull. By measuring how wide this hole is, we can figure out how much blood is flowing to the brain and, by extension, how active the brain is. So, measuring brain volume isn’t the best way to measure intelligence.
The development of man
Above, the development of man is broadly outlined. Man has proven to be very successful. We’ll dive deeper into the reasons behind this success in the next part.
Man learned to walk upright
Man has started walking upright in order to have his arms free for the use of tools. The use of tools was a huge evolutionary advantage. Being able to walk upright did require drastic physical adjustments: in the foot and especially the big toe to be able to make that last push when walking; in the knee joint to be able to stretch the leg; in the hip joint to bring the thigh into a vertical position; in the back that became straight so that the head is perpendicular above the legs and finally the face that became flattened so that we could see what is in front of us.
Running hard became possible
Hunting required speed, so humans evolved slimmer bodies and longer legs. Human legs are half the length of our bodies. But it wasn’t just the longer legs that made us fast runners. When we run, we can put our feet more in front of each other than apart. This is crucial because if our feet are spread too far apart, we create a swaying gait that makes running fast impossible. By putting our feet more in front of each other, we can run fast.
However, women still had a limitation. A large birth canal hindered fast running. This required adjustments. Women therefore got wider hips than men. Another adjustment is a relatively smaller head of the baby. In humans, the baby head at birth is only 29% of the adult head. In chimpanzees, this is 47-48%. After birth, the head must therefore grow much more. These adjustments did help but turned out not to be entirely sufficient. Births of human babies are therefore more problematic than births in the animal kingdom, requiring more assistance.
Overheating was brought under control
So, when humans started running fast, they got overheated. You see, modern humans evolved in Africa, where it’s super hot. If you start running fast, you’ll quickly overheat. To combat this, humans developed more sweat glands and lost their hair. This way, they could sweat more and cool down faster. But here’s the catch: Africa gets a lot of sun, so they needed to develop a black pigment to protect their skin from the sun’s harmful rays. Interestingly, the part of modern humans that migrated to Europe around 50,000 years ago lost that black pigment because the sun shines less often and less brightly in Europe.
Man became more intelligent
Big brains are the key to intelligence. So, how did we get those big brains? Well, it all started with learning to control fire. Fire was a game-changer! It allowed us to cook our food, and guess what? Our bodies can absorb cooked food better than raw food. So, we could get away with smaller jaws and shorter intestines. And here’s the cool part: we saved energy by doing this. That energy went straight into our brains, making them even bigger and smarter!
Prehistoric man cooks with fire
But those bigger brains also came with some challenges. In animals, the brain is set in stone from birth. Animals are usually pretty self-sufficient right away because of their instincts and reflexes.
The human brain isn’t set in stone at birth. Babies are therefore super helpless! However their brains are super active, and they constantly learn and connect things. This is called associative learning, and it’s super important for intelligence. But it also has a downside: it takes a lot of time. So, the time when babies are totally dependent on us is pretty long. That’s the price we pay for our brains!
Modern man originated in Africa. However, modern man has not stayed there and has populated the whole world from Africa. Among other things, he came into contact with the Neanderthals. This is the subject of the following article.
3. The Evolution of Man