Between 150,000 and 30,000 years ago there were at least eight different species of humans sharing the planet. There might even be more. And it is well known that these groups shared spaces and even exchanged their genetic material by interacting with each other.
Currently, however, that miscegenation no longer exists. "Today is a very unusual time in terms of human evolution," explains molecular archaeologist Tom Higham. "For several thousand years, we shared the planet with different groups of hominins and now it's just us and our great cousins the apes," he adds.
Higham has spent 15 years working closely with his colleague at the University of Vienna, Katerina Douka, examining ancient bone and tooth fragments using state-of-the-art scientific methods to try to find the answer to this puzzle.
Their conclusion is that our ancient cousins are more present in modern human DNA than we thought. Our genetic code, for example, has a small proportion of genes from archaic groups like the Neanderthals. Every person with a European or Asian background has an average of 2% Neanderthal DNA in their blood. For people of African origin, the percentage is lower.
This explains not only some genetic dispositions in modern humans, but is also evidence that different human species had contact more than 40,000 years ago, the researchers explain in an article published in the journal Science Advances.
Higham and Douka analyzed a small bone found in 2015 in a Denisovan cave in Siberia, perhaps one of their most important discoveries. “Mitochondrial DNA initially assigned it to a Neanderthal. However, after fully sequencing it, we discovered that it belonged to a girl about 13 years old whose mother was Neanderthal, but whose father was Denisovan. This was the first time that anyone had found a so-called 'F1 hybrid', a first-generation offspring of two different types of humans."
The last 20 years have seen an explosion in this field. There were fierce debates among specialists about whether the different species could have been found, something that changed profoundly 12 years ago with the publication of the Neanderthal genome, which showed that people living today carry part of the Neanderthal DNA.
"Before 2010, such analyzes weren't possible because the methods didn't exist then. Now we can take a few milligrams of powder from small archaeological bone fragments, identify them by species, and thus find possible hidden human bones. It's quite amazing how the methods to examine remains have improved so dramatically," says Tom Higham.
There are tons of ancient bones stored in archives around the world that can now be correctly identified. "In this way we will be able to find previously hidden potentially human fragments, such as that small Denisova bone," says the researcher.
But not only the methods for examining human remains have improved. Modern archeology uses techniques from a wide variety of disciplines, including laser and satellite technology, artificial intelligence, electron microscopy, computed tomography, particle acceleration, and many more.
"Modern archaeological methods, such as the study of ancient DNA, show that there were numerous times when different human groups intermingled, and that the entire world population today is closely linked genetically," adds Higham.
In the 1970s, an approximately 11,000-year-old human skeleton was found in Cheddar Gorge in Somerset, England. The technology made it possible to reconstruct what the person must have looked like when he was alive: the so-called "Cheddar Man" had dark skin and light blue eyes, a phenotype that does not exist today.
"However, we know that this phenotype was common in other parts of Western Europe. So what happened? The first Homo sapiens to arrive in Eurasia had darker skin because they originally lived in warmer areas. The lighter skin only arose in Europe in the last thousands of years, with the arrival of peasants from the Middle East", continues the archaeologist. The latter are believed to have gained importance because the light pigmentation facilitates the synthesis of vitamin D.
"We found evidence -concludes Tom Higham- of human behavior in Africa that is more than 100,000 years old. Early forms of symbolic art, drawings and surface designs applied to ocher pieces, the first ornaments and jewelry made from shells and eggshells, animal teeth with holes drilled for wearing around the neck…”.
