Remains of the DNA
For the first time, scientists have retrieved the DNA of extinct humans from sediments in caves.
This article appears in the Witness section of the Summer 2017 issue of the New Humanist. Subscribe today.
Tens of thousands of years ago, in a cave in Belgium known as Trou Al’Wesse, a Neanderthal died. Some 45,000 years later, in 2015, a group of scientists found its DNA in the sediment of the cave rocks. This DNA had stuck to minerals in the sediment after the Neanderthal died and its cells split apart, and persisted long after the body itself had disappeared.
Until the scientists made this discovery, there was no definitive evidence that this Neanderthal had lived and died there, as its bones were never discovered. There were stone artefacts and animal bones with cut marks, which strongly suggested that ancient humans had been present – but without the bones themselves, it was impossible to say for sure. Until now.
Scientists who study living animals have long used environmental DNA to identify creatures. It is a useful technique when studying rare or difficult-to-identify species in hostile environments. Examining the genetic material that ends up in the air and soil allows scientists to examine the natural world without the animals themselves. For about 15 years, the same techniques – drawing on the vast genetic aura that animals give off into the world around them – have been used by palaeontologists to study prehistorical creatures such as mammoths.
But this is the first time that scientists have established that the DNA of extinct humans can be retrieved from sediments in caves; previously, research has focused on skeletal remains by necessity. The research, published in the journal Science, looked at genetic material in sediment samples collected from seven different archaeological sites, in Belgium, Croatia, France, Russia and Spain.
The samples covered a huge timespan – from 14,000 to 550,000 years ago. In the lab, scientists fished out tiny fragments of mitochondrial DNA: genetic material passed through the mother that is particularly effective for telling apart closely related species. Even sediment that had been stored at room temperature for many years yielded DNA. They found samples from Neanderthals and Denisova, a recently discovered sub-species of ancient human. “This work represents an enormous scientific breakthrough,” said Antonio Rosas, a scientist at Spain’s Natural Science Museum.
Fossilised bones from ancient humans are scarce, even when circumstantial evidence – like the discovery of stone tools – suggests that they were present. The discovery that human DNA can be found in caves opens up the possibility of establishing the identity of inhabitants of sites where only artefacts have been found. Researchers will be able to tell which species occupied a cave, even where no bones are found. Eventually, they might also be able to study when they arrived and how long they stayed. It opens up a world of possibilities in a previously limited field of research.