Homo erectus in our DNA?
A Denisovan could pass on to a modern person the genes of his most distant ancestor
Our distant ancestors, belonging to the species "Homo erectus", inhabited the island of Java, now the most populous island in Indonesia, about one and a half million years ago, when Java was not yet an island. Until now, it was believed that they died out half a million years ago and therefore did not leave a trace in the genome of modern humans. However, the latest findings of archaeologists suggest that about 100 thousand years ago, erectus still lived in Java and could transfer their genes to modern man through a Denisovan!
Not so long ago, the genealogy of mankind seemed to be a straight line, but today we know that many human species that lived not only in Africa, but also in Eurasia participated in the formation of a modern anatomical type of man. Traces of these ancient people can be found in the genome of our contemporaries.
For example, all people of non-African origin carry the genes of Neanderthals. As for the Denisovans, their genetic trace is well traced in the peoples of Papua New Guinea and Australia, China and Japan… For example, the genome of modern Papuans, inhabitants of New Guinea, contains about 4% of the genes of Denisovans. However, it also contains about 1% of archaic DNA that does not belong to the studied genomes of ancient people. This fact may be evidence of hybridization between Denisovans and Homo erectus.
The whole catch is that the Denisovans, who settled New Guinea, separated from their Altai relatives about 300 thousand years ago. And their supposed "partners" erectus in Africa and mainland Asia died out about half a million years ago. At least, it was thought so until recently.
This is what a human family tree looks like, built using paleogenetic data. The red arrows and numbers show gene flows between different groups of primitive people and their contribution to the gene pools. From the presentation of Paleogeneitic S. Paabo (Max Planck Society Institute of Evolutionary Anthropology) at the seminar "The origins of the Upper Paleolithic in Eurasia and the evolution of the genus Homo". Gorny Altai, July 2018
H.erectus formed about 2 million years ago in Africa, causing the first wave of hominin settlement on the planet. About 1.6 million years ago, erectus inhabited Java, which at that time was still connected to the land by a land bridge. But when people of the modern anatomical type came to Java 40 thousand years ago, they had not been there for a long time.
In the 1930s, Dutch researchers excavated near the Solo River and found many fossil animal bones, as well as partially preserved skulls and leg bones belonging to H.erectus. They could not date the finds accurately at that time. Later, data on their location were lost, and in order to obtain dating by modern methods, it is necessary to have, in addition to fossils, samples of sediment layers where the finds were made.
It was possible to find the excavation site already in this century from photographs and notes by Dutch archaeologists. In 2008 and 2010, new fossils were found there. Using several methods of radioisotope dating, the researchers found that erectus still lived in Java 108-117 thousand years ago! About 130 thousand years ago, the sea level rose, and Java turned into an island. In a warmer and wetter island climate, a tropical forest has grown in place of the savannas, and the erectus probably could not adapt to the new conditions.
For modern science, the erectus of Java is the "youngest" of all known, although it is impossible to say with certainty that they were the "last". In any case, this finding suggests that in the Middle Paleolithic era, erectus theoretically could have formed a "company" of Denisovans and passed their genes through them to modern man.
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