I'm having an existential crisis.. if we humans come from apes, why didn't they evolve like us? How did humans started to eat meat and dominate the fire? Why are there more intelligent animals than us and why aren't they the ones in control of everything? It is true that we have a close relationship with reptiles?
I’ll answer this part by part!
1) “if we humans come from apes, why didn’t they evolve like us?”
First of all, evolution doesn’t plan ahead and isn’t driven towards some sort of goal or end point like humans, and there’s nothing inherent about apes that means they will evolve into humans. Instead, evolution is a process of natural selection, which works like this:
- Living things vary - humans for example show differences in height, weight, body type, skin/eye/hair colour, resistance to certain diseases, blood groups, intelligence, athletic ability, sight/hearing, etc. Some of this variation can be passed on genetically, from parents to children.
- New variations occasionally turn up through mutation - a random change in the genetic code. Some of these new traits are very minor and are of no consequence, some new traits are harmful to the individual, and some new traits are helpful and improve an individual’s chance of surviving long enough to reproduce.
- Not everyone gets to reproduce. In nature, there is fierce competition for resources like food, water, territory, mates, light (for plants), etc. Most individual organisms will die young and never make it to adulthood; those that do make it to adulthood may never find a mate. Only a tiny fraction of organisms ever get to reproduce and pass on their traits to the next generation.
- Who gets to reproduce is not random. Living things with traits that aid survival and reproduction are more likely to… well, survive and reproduce… and pass those beneficial traits on to the next generation. Living things with harmful traits are less likely to survive and reproduce, and more likely to die before they can reproduce and pass those traits on.
- This means that over many generations, a population of organisms will gradually become better adapted for survival and reproduction in their environment, as new traits emerge through mutation, those that aid survival and reproduction get passed on through the generations and those that are harmful die out.
Natural selection is sometimes described as “survival of the fittest,” but when you hear that phrase you should realise “fittest” doesn’t necessarily mean biggest and strongest (although it can). “Fittest” just means “best able to survive and reproduce in this particular environment.” Sometimes the “fittest” organisms are the fastest, in other situations they’re the slowest. Sometimes they’re the biggest, sometimes they’re the smallest. Whatever leads to greatest chances of survival and reproduction! It all depends on the environment these organisms are trying to survive and reproduce in.
And this means that if one species is spread throughout many different environments, natural selection will act in different ways, as different traits will be needed for survival in those different environments. After enough time, that one species may split into two or more species as the differences build up over the generations and these different populations adapt to different environments.
Something like this may have happened with humans and other apes. Fossil evidence shows our early ancestors lived in Africa, and more closely resembled modern apes than they resemble modern humans. Africa in those days was warmer and wetter than it is now, and covered in forest/jungle - and apes are well adapted to this kind of environment. But as the climate changed, parts of Africa became drier and sparser and became the savannah - scattered trees and grass instead of the heavy forests the apes were used to. Those who remained in the forested parts of Africa (e.g. west central Africa) became today’s chimpanzees and bonobos; those who found themselves struggling to survive on the savannah were subject to higher natural selection pressures and ended up developing new advantageous traits (e.g. upright walking to get around without trees to swing through, tool use, larger brains and more complex social co-operation to survive in an environment where resources are scarcer than in a rich jungle) to deal with this new environment, and went on to become our ancestors. (I should note that not all palaeoanthropologists are convinced that our uniquely human traits are adaptations to the savannah, but my main point still stands - humans and chimpanzees/bonobos are adapted to different environments, and natural selection has pushed them in different evolutionary directions to best survive and reproduce in those environments. They’ve also had different random mutations as well after their ancestral lines have been separate for six million years!)
(The jungles of west/central Africa vs. the savannah of eastern and southern Africa. About ten million years ago, most of Africa looked like the first picture; by five million years ago, the ancestors of chimpanzees and bonobos were living in an environment like the first picture while human ancestors were forced to adapt to life in the second. Sources: 1, 2)
So part of the answer to your question is that evolution has no forward planning and no ultimate goal, and there’s no reason to expect apes to evolve into humans. Natural selection only cares about what allows you to survive and reproduce in the here and now, and depends on chance factors such as random mutations in your genetic code and changes in the environment around you. All of today’s apes, and humans, and all other organisms are constantly evolving in their own, unpredictable ways - adapting to whatever the environment and genetic mutations throw at them through natural selection, and not “aiming” at any kind of goal like “become more human.”
A second thing I should mention is that humans did not evolve from chimpanzees, bonobos, gorillas, or any other living species of ape. Instead, humans and chimpanzees/bonobos are both descended from the same extinct species of ape who lived around six million years ago in Africa - we share a common ancestor. We are related to chimpanzees and bonobos (like cousins or siblings or aunts/uncles), but we are NOT descended from them (like parents or grandparents). Go back a few million years more and humans/chimpanzees/bonobos share a common ancestor with gorillas. Go back even further and we share a common ancestor with orangutans.
Incidentally, you can see from the diagram that a chimpanzee or bonobo is more closely related to a human than to a gorilla, and that chimpanzees, bonobos and gorillas are all more closely related to humans than they are to orangutans. This is why biologists today classify humans as a species of ape. We fit neatly in with that family. Not only are we related to or descended from apes, we are apes right now!
2) How did humans started to eat meat and dominate the fire?
That’s something nobody really knows. Most of the apes eat little meat - chimpanzees, bonobos and orangutans are all mostly vegetarian with a tiny bit of meat thrown in and some insects for good measure, while gorillas are entirely vegetarian. So while we can’t say for certain it’s probably a good bet that the common ancestors we shared with these species were mostly vegetarian too, with a little meat and insects in their diet for good measure.
We think human ancestors started eating meat in a big way about 2.5 million years ago (around the time of a species called Homo habilis), because that’s around the time we first find stone tools useful for slicing into meat and animal bones with marks on them showing the meat has been hacked off by someone with a stone tool. We don’t know why those early humans started eating meat in a big way, but this article speculates it was to help deal with competition from other similar species (chimpanzees and gorillas can coexist in the same region because they have different diets and don’t need to compete for the same food; perhaps our ancestors evolved a taste for meat for the same reason, to give them a unique food source that they wouldn’t be competing with other species for).
(Homo habilis eating meat. Source)
Meat had a big impact on the human body. Because meat has a higher fat and cholesterol content than vegetable food, humans can handle a much higher level of fat and cholesterol than other great apes can (although our modern, Western processed diets are too much even for our own bodies!) Adapting to eating large quantities of meat also changed our teeth and our digestive systems. But most importantly, since meat is high in calories, eating meat gave us a great deal of extra energy - energy our brains could use to grow and develop. When you consider that the human brain uses about 20% of our total energy reserves, you can see how a meat-eating species could more easily grow larger and more complex brains than its close relatives. (Note that I’m talking about all this in the context of prehistoric Africa! In a modern city with a great deal of choice in the supermarkets it’s entirely possible to get the calories and protein our bodies and brains need (and, for most of us, to eat way more calories than we need) on a vegetarian or vegan diet alone. Meat-eating may have been necessary to support our energy-hungry bodies and brains back then, but it isn’t now).
Fire is a much more recent innovation, but it’s difficult to tell whether fossilised ash found near human remains is the remains of a deliberately started fire or just a natural fire that happened near where the humans happened to live and/or die. Looking at evidence like how the soil is magnetised has led experts to estimate that humans began starting fires anywhere between about 200,000 and 1.7 million years ago, with the majority expert opinion being that humans started to use fire around 400,000 years ago. Homo habilis was long gone by this time and the first human species to use fire was probably Homo erectus, although it could have been the closely related Homo ergaster. (In fact, not all palaeoanthropologists agree erectus and ergaster are different enough to be considered different species - they could just be different variations within the same species. There’s an awful lot of open debate and discussion in this field since there’s not a lot of hard evidence to go on!)
(Homo erectus using fire. Source)
How we started using fire is a bit of a mystery. Perhaps our ancestors first saw naturally-started fires, caused by lightning or lava, and tried to capture some fire for themselves and keep it burning for as long as they could. Maybe this was pure curiosity at first, but eventually they figured out how useful fire could be, and through trial and error and experiment learned how to start fires themselves. Fire gave our ancestors many advantages, such as light, heat, defence against predators, a weapon against enemy tribes, and fire could be used to cook food to kill off disease-causing bacteria (not that our ancestors back then would have realised that’s what they’re doing!), making that precious high-calorie meat softer and easier to chew/digest, and making tough plant foods easier to digest too.
Over time we see the teeth of fossils of Homo erectus get smaller, perhaps as cooking spread around the world and people everywhere got used to eating a softer and less chewy diet. Around this time humans start to be born without wisdom teeth, our jaws shrink, and some humans get the annoying problem of impacted or partially erupted wisdom teeth that plague so many of us today - thank cooking for that! Cooking did have a positive effect though despite the wisdom tooth problem - it meant a wider variety of foods were now edible and safer to eat. Humans could eat more calorie-rich meat and a wider variety of vegetables, getting more nutrition and being able to find food in environments their fire-less ancestors couldn’t have found food in.
So why only humans and not any other species? Part of the answer lies in our hand structure, as humans have the manual dexterity needed to start and control fires. But it is true that while most animals simply fear fire and run at the sight of it, humans have a strange fascination with it. Perhaps this is because most animals only instinctively see the danger in fire, while humans can imagine the possibilities - we can look at a fire and imagine its warmth and light being put to good use. So perhaps the most important reason we are the only animal on Earth with control over fire is because only we have the imagination required to see how fire can be a friend! Which brings me to…
3) Why are there more intelligent animals than us and why aren’t they the ones in control of everything?
Intelligence is a pretty hard trait to measure objectively but by almost every measure of “intelligence” humans come out on top. There are no other animals alive today (although our closest cousins, the Neanderthals, may have had similar mental powers to us) who can rival our species in brain complexity, the complexity of our language (other animals use sounds and gestures to communicate, of course, like barking dogs or singing birds, but their “vocabulary” is much smaller than ours and the grammar is either really simple or non-existent), or our ability to understand abstract reasoning. Absolute brain size isn’t a good measure of intelligence, since a big animal like a cow will need a much bigger brain to co-ordinate its huge body than a little animal like a rat. (However, just about everyone agrees rats are more intelligent than cows!) Brain size in relation to body size is a better measure (although even then, that’s not guaranteed, since different brains may be organised differently internally and may be adapted to different functions besides complex thought). But humans come very close to having the largest brain in proportion to our body size for a mammal. (We do have a competitor, however…)
Many other species can be quite intelligent. Other great apes, like chimpanzees, bonobos, gorillas and orangutans, can understand pretty complex concepts, can master a fairly large vocabulary if trained to use sign language, and have been known to make and use simple tools in the wild - not surprising, considering our brains and their brains recently evolved from the same common ancestor (although our brains are still far larger in proportion to our body size and much more complex, and our tool use, language and capacity for abstract thought and problem solving are hugely superior to that of other apes.) The problem solving skills and memory of of crows can rival that of young human children. Dogs, especially intelligent breeds like the border collie, can learn hundreds of words and can be trained to understand simple arithmetic problems. African Grey Parrots can understand - and speak - a lot of human language as well. Elephants are highly intelligent too. And dolphins may be second only to humans in intelligence - their brains are larger than ours, despite being similar in size, and their cerebral cortex is more convoluted (although remember what I said earlier, those brains could be adapted for other functions besides complex thought!) Dolphins do display an amazing degree of self-awareness, problem-solving abilities, use simple tools, and have a complex social structure and system of communication (while their system of clicks and whistles isn’t nearly as complex as our own languages, they can understand some limited human sign language). However, some researchers think that the evidence for dolphin intelligence has been overrated. Look up John C. Lilly for the main proponent of dolphin intelligence, and Justin Gregg as the main proponent of dolphins being an unimpressive, slightly above-average mammal.
Despite all this, there’s no evidence that any of these animals are anywhere near as intelligent as humans are. It’s difficult to imagine even the chimpanzees or gorillas pondering the meaning of existence or wondering where the Universe came from, or creating great works of art or music. And if the dolphins have the mental capacity for all of this (which they probably don’t), their aquatic environment has led them to evolve flippers and a streamlined body for swimming, so they don’t have the manual dexterity of the human hand required for anything like writing or complex technology (and you can’t master fire under water!) So humans almost certainly are the most intelligent animals on Earth.
“On the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much - the wheel, New York, wars and so on - whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man - for precisely the same reasons.“ - Douglas Adams, the Hitchhiker’s Guide to the Galaxy
But I should also point out that intelligence doesn’t necessarily mean dominance of the planet (like I said, even if dolphins were more intelligent than humans, their flippers mean they still couldn’t control their environment the way we can with our hands). Humans arguably dominate the planet today (although the insects far outnumber us, earthworms have a much greater impact on the environment through their turning and fertilising of the soil - and a much more positive impact on it than humans have had so far, if we’re honest! - and bacteria far outnumber everything else on this planet, with humans completely dependent on them for survival, so even then our dominance over the planet is questionable), but a hundred million years ago, our mammal ancestors were unquestionably subordinate to the ruling dinosaurs - even though they were unquestionably more intelligent than them. Intelligence isn’t everything!
Speaking of dinosaurs and mammals…
4) “ It is true that we have a close relationship with reptiles?”
Every living species on Earth is related to every other living species, so humans are indeed related to reptiles! Our last common ancestor was a small lizard-like species who lived around 300 million years ago. One line gave rise to today’s reptiles, including turtles, snakes, lizards, crocodiles and birds (as we now know birds are a specialised group of dinosaurs, the only ones that survived the mass extinction 66 million years ago). The other line gave rise to the now-extinct “mammal-like reptiles” or synapsids, who in turn gave rise to all the mammals. The whole group (reptiles, birds and mammals) descended from this common ancestor is called the amniotes and the family tree of all living amniotes (showing how we’re related to reptiles and birds) is shown below:
We share a lot of features with reptiles - our basic anatomy is very similar, with more or less the same organs and skeleton (with a few minor differences) in more or less the same place. Even some of our basic brain functions can be traced back to reptiles - some birds are pretty intelligent after all! We’re closer to reptiles than we are to amphibians, fish, or any invertebrates - that is, any animals other than mammals. And of course, we’re closer to other animals than we are to fungi, plants, protists, archaea or bacteria, so reptiles are pretty close relatives of ours in the grand scheme of things!
But we share a lot more in common with other mammals (walking with our legs underneath us instead of sprawled out like reptiles do, hair/fur, warm blood, a more complex brain, differentiated teeth, sweat, milk glands, bones in our middle ear, no nuclei in our red blood cells and a four-chambered heart, amongst other things) than we do with reptiles, and we share much more recent common ancestors with the various mammal groups than we do with reptiles. Amongst the mammals, we’re more closely related to the primates (lemurs, tarsiers, monkeys and apes) - we share more physical features and more recent common ancestors - than any other group of mammals, we’re more closely related to apes than any other group of primates, and as I mentioned earlier our closest living relatives are chimpanzees and bonobos, who we share a very recent common ancestor with.
It’s all connected!
Hope that answers some of your questions about humans, anon!