When did humans appear?
Lately, I've been wondering when humans appeared.
Well, it is impossible to say from what moment a species in the fossil record can be considered human, there is a transition of traits that appear during geological time.
Let's start with what we have now, humans are part of the “Great Apes”, along with orangutans, chimpanzees and bonobos, We are in the Hominidae family, the hominids, the truth is that we are not that different. But there is something that clearly distinguishes us from other hominids. No, I'm not talking about intelligence, our relatives are quite intelligent.
The difference is that we walk upright, erect, that is a trait exclusive to humans. There are other bipedal animals, but they have tails to swing and are not completely upright. We call Hominids that walk upright Hominins. Should we consider that being hominin is synonymous with human? Yes, but no. Yes, because we are currently the only Hominin; but no, because until very recently there was a good variety of hominins, not necessarily humans.
When did hominins appear? Good question. We must review the fossil record, the first thing is that fossils do not appear progressively, it is more likely that the most recent remains appear first and the older they are, the more difficult it is for them to appear. The first records of bipedal Hominids come from the 20's of the last century, from then on they appeared more in the eastern part of Africa, and several species appeared. In the 1960s, the remains of a bipedal animal appeared in Tanzania, and in some sites associated with its remains the first stone tools were found. A tool-making hominin! And it occurred to them that this was already a human trait and it was defined that the genus Homo was made up of hominins with the ability to make stone tools, and the members of these remains were called Homo habilis, the “skillful man”, who lived between 2.3 and 1.9 million years ago.
Remains continued to appear, I will mention them in the chronological order in which they lived, not in which they appeared. First Sahelanthropus tchadiensis, about 7 million years ago, very few remains, due to characteristics of the skull it is assumed that it could walk upright. Then, about 6 million years ago, Orrorin tugensis, although few remains, due to the characteristics of the femur found, could be bipedal. Then come the Ardipithecus, between about 5.8 and 5 million years old, two species, of which there are more remains and it can be concluded that they already walked upright, but because of the phalanges of their hands and, especially, that the thumb of their feet was still opposable to the other fingers, it is known that they still spent a lot of time in the trees. Let's say they were facultative bipeds. My opinion is that these three groups were not yet hominins, they lived in mainly arboreal environments, which put an end to the theory that bipedalism began in the savannahs.
The next group are the Australopithecus, a very successful group, at least five species were found in Eastern and Southern Africa, the remains that I mentioned that were discovered in the 20's are from one of these species. The best known remains is “Lucy”, one of the most complete fossil remains to date. These yes, without a doubt Hominins. They lived between 4 and 2 million years ago.
Contemporaries of the Australopithecus we find Kenyanthropus platyops, about 3.5 million years ago. There are very few remains and they are very deformed, some consider that it could be a type of Australopithecus. Paranthropus, similar to Australopithecus, but with cranial adaptations for a massive chewing apparatus, are called “The Nutcrackers.” They lived between 2.5 to 1 million years.
Then Homo habilis appears and, contemporary, H. rudolphensis, the hominins who made stone tools, the first humans, but… is that true?
It turns out that stone tools, being made of stone, are preserved very well. Remains of these are often found, but not of the hominin that produced them. It also happens that nearby remains of hominins are found, but how do we know if they made them?
Well, it turns out that the oldest evidence of stone tools is from 3.3 million years ago, very crude, but undoubtedly worked to be used as tools, at that time H. habilis still didn’t appeared, so someone else made them, in the area where they were found they could have been made by Kenyanthropus platyops or by Australopithecus afarensis.
Well, but these tools were very crude if we compare them with the tools of Homo habilis, there is more refinement, although they are still simple. Well yes, it may be, but the tools with these oldest characteristics are from 2.6 million years ago, Homo had not yet appeared.
So saying that Homo are tool-making hominins no longer applies. We could say that from the Australopithecus to the first Homo were archaic humans. But to consider them as Homo there must be something more...
What's more, if we see the anatomical proportions of these archaic humans, we will find that in all of them, the relationship between the extension of arms and legs is very different from ours. Their arms are proportionally much longer than ours. This affected their walking, they must not have been very fast and they must not have had much stamina.
What determined that in modern humans the size of the arms decreased and the legs lengthened?THE ENDURANCE RACE!
And that appeared with Homo erectus, about 1.9 million years ago, my opinion is that he was already totally human.
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