Why did they disappear? (pub. December 20, 2024)

Bullfight on Wednesday, December 18

Friday, December 20, bullfight

I hesitated to get up today, Friday, to run, yesterday I had a very good time with dear friends and I ate too much, so I didn't sleep well. Fortunately, I did run.

This month, there were two news stories about human ancestors that caught my attention. The first was the discovery of fossil footprints of Hominins, which is what they call the great apes (Hominids) that walk upright. They were discovered in Kenya in 2021, but the conclusions have only been published until now. Of the footprints, there are some that are perfectly human, the others have some details that make them different, their age is about 1.5 million, we did not exist at that time, but if the Homo erectus, who from the neck down were the same as us, so the human footprints are theirs. Of the others, the study concludes that they are Australopithecus (Paranthropus) boisei. Another interesting thing, the authors of the study conclude that the footprints were made with a very small difference in time between them. This is interesting, it has long been known that these two species corresponded in time and space, but there was a discussion whether they would have actually encountered each other. These footprints show that they did.

We know that more recent hominin species had also coincided, which brings me to the second news. The identification of a new hominin species, with an age of approximately 200 thousand years, lived in East Asia, in a place that is now China. In East Asia there is a great variety of human species between 300 thousand and 50 thousand years old. Curious things, this new species was very big-headed, to give a reference the Neanderthals (H. neanderthalensis) had a cranial capacity of about 1,400 cm3, we, the H. sapiens, have a slightly smaller capacity, around 1,350 cm3. The new species has a capacity of more than 1,600 cm3, it was given the name of H. juluensis, Ju Lu in Chinese means “big head”. Like the Neanderthal, the big-headed man had an egg-shaped cranial vault, with a very elongated occipital lobe. Our cranial vault is rounder. At that time there were other humans in Asia, at least H. erectus, which had spread from Africa to Asia, and the dragon man, H. longi, another species that was only recently recognized in 2021. Did these humans meet each other? It is very likely, but there is no evidence that this was the case.

I needed to comment on something, in the study describing the bighead it is speculated that the Denisovans are probably its descendants.

Was there another time and place in which different types of humans have coincided? Yes, and very recently.

Let's start with Africa. Some 250,000 years ago, we, H. sapiens, were already lurking around, but not alone. There was another human, very similar to archaic humans, but who had remained until then, H. naledi, described only in 2015. It coincided with us in South Africa in time, but there is no evidence that we met.

Then humans left Africa and began to meet other relatives, but some of these relatives found each other. For example in Siberia, in the Altai mountains, we know that the Neanderthals lived with other relatives, we have little information about the latter, the most of what we know about them is from the genetic material found in bone remains in a cave, Denisova, in those mountains, hence their common name, Denisovans. In Denisova there are remains of these two relatives. This was between 80 thousand and 50 thousand years ago.

We know which Neanderthals and Denisovans mixed, conclusive evidence. Some remains in which it has been determined that the mother was Denisovan and her father was Neanderthal. One girl, Denny, is the only known first-generation human-species hybrid.

Although there are very few remains of Denisovans, we know that they spread throughout Asia. There are remains in Tibet and Laos, but they are so few that they are not yet officially recognized as a species.

But back to us, we left Africa and arrived in the Middle East and Africa, where we met the Neanderthals, between about 100 thousand and 40 thousand years ago, there is a lot of evidence that we were in the same places at the same time.

But we also reached Asia, where we meet the Denisovans, estimated between 50 thousand and 30 thousand years ago, probably less. There isn't much physical evidence of the coincidence, but there is other evidence, which I'll talk about in a bit.

But if you have read this blog before, you will remember that at that time there were other relatives in Asia, the erect ones were still present, but there were also the hobbits (H. florensensis) and the Luzones (H. luzonensis). Will we meet them? Nobody knows, there is no evidence.

But there is no doubt that we coexisted with the Neanderthals and the Denisovans, there was even sexual exchange, how do we know?, because of our genome.

Studies comparing the genomes of Neanderthals and Denisovans with our own show that between 1 to 4% of our genome is Neanderthal, the largest percentage being found in humans who have European ancestry.

Do we mix with the Denisovans?, without a doubt.

In current humans of Asian ancestry, there is more than 2% of the Denisovan genome. But in the islands of Melanesia it reaches up to 6%. 

But it gets even more interesting. When comparing the genomes of people from Indonesia with those of Neanderthals, Denisovans and other humans, something surprising was found: the Denisovan DNA of the people of New Guinea is different from that of the rest of the Denisovan genomes in humans. What's more, it could be that these Denisovans had mixed with some other human, older than the Denisovans and Neanderthals, erect, big-headed or dragons?

Why did such a variety of humans who lived so recently disappear?

Well, speculating, humans have a characteristic: we are ecologically very aggressive: where we arrive, we monopolize everything and leave nothing available for other humans.