The meeting with a relative of a strange and powerful man – the Denisovans – has left a mark on the security of modern Papuans, especially those who live on the island of New Guinea.
This is a new discovery that we describe in a study published in PLoS Genetics today. It also shows that our current diversity didn’t just evolve – parts of it we got from other groups, which died out.
DNA from our evolutionary cousins
Humans are the only living species Homo color. But up until 50,000 years ago, our ancestors coexisted – and sometimes interacted – with several others. Homo groups around the world. Most of them we know only from fossilized remains, which provide a fascinating glimpse of our evolutionary cousins.
But for two groups there is something else: DNA. Thanks to advances in technology, scientists have taken DNA from fossils and sequenced them. As a result, we now have a complete sequence of the known genomes of the archaic hominins, the Neanderthals, and the more complex group, the Denisovans.
Although Neanderthal fossils have been unearthed all over Europe since they were first discovered in the 1860s, the number of known Denisovan remains fits in the palm of your hand – literally!
The shape of the genome we have comes from the smallest bone in the pinky finger. It belonged to a 60,000-year-old teenage girl from a cave in Siberia, the oldest Denisovan fossil until recently.
Parental signs
These genome results have changed the way we think about our extinct relatives. First, he quickly showed that when people grew up outside of Africa, we had sex – and children – with other people.
Their genomes remain in people alive today, transmitted from generation to generation.
In the case of Neanderthals, the following are present in all modern non-Africans. In the case of the Denisovans, we find a small amount of their genome in people from all over Asia – especially in Papua New Guinea, and in the islands of Southeast Asia, where people may owe 4-5 percent of their genes. parents.
But knowing the DNA fragments in our bodies is just the beginning.
DNA makes a difference
The real challenge is to find the biological results of this DNA in the people who carry it – which, remember, is the majority of people. Our specific research question was to describe the molecular mechanisms that may be affected by its presence.
Studies of Neanderthal DNA have shown that genetic variations from them can alter the levels at which certain human genes are expressed, e.g. We also know that Neanderthals have contributed to our immune systems (including differences in how humans react to the virus after contracting the COVID-19 virus), and to changes in skin and hair.
But it has not been known whether Denisovan DNA has left any similarities with modern humans.
In 2019, a study revealed a genomic link where Denisovan DNA can be found in the bodies of Papuan people – meaning the people of New Guinea Island – who are alive today.
This led us to look into these areas, to understand the cellular and biological processes that may be affected by Denisovan DNA. We took a hybrid approach to this question, making numerical predictions first, followed by laboratory-based experiments to confirm our findings.
Additionally, we took advantage of the Neanderthal DNA identified within these populations to highlight any Denisovan contributions. This provided us with an integrated understanding of how these kin encounters left ecological and evolutionary consequences in modern humans.
A unique Denisovan offering
We found that the Papuans, Denisovans and Neanderthal species sometimes occur in genetic regions that cause changes in nearby genes.
However, only Denisovan species are predicted to occur and affect factors that control the expression of immune-related genes.
Thus, different sources of DNA may contribute to genetic and phenotypic diversity within Papuans in different ways.
To confirm our predictions, we conducted an experiment comparing five Denisovan genes against their modern counterparts, and tested their ability to influence the expression of a specific type of immune system known as lymphocytes.
In two of the five cases, the Denisovan species had a different effect on gene expression than their modern counterparts. And they affect genes that are known to be very effective in fighting pathogens, including viruses.
The fact that the Denisovans, but not the Neanderthals, seem to have contributed to the immune systems of modern Papuans tells us something more about these ancient people.
Although little is known about how the Asian Denisovans lived, it shows that their immune system evolved to adapt to the infectious diseases that lived in their environment.
When humans migrated 60,000 years ago, the tiny bits of DNA they carried with them made it possible to colonize this part of the world.
Although our study is the first to describe the contribution of Denisovan DNA within modern human species, there are still interesting questions to be answered. In particular, it is not known whether the overall contributions of Denisovan and Neanderthal genetic variants differed over time.
It is also important to note that we tested different genetic variants in immune cells in the respiratory tract. This means that the same genetics or other species can have different effects on the environment – this will be an important question for future studies.
Irene Gallego Romero, Senior Lecturer in Human Genetics, The University of Melbourne and Davide Vespasiani, Post-doctoral Researcher, The University of Melbourne.
This article is reprinted from The Conversation under a Creative Commons license. Read the first article.
