Cave Mud Neandertal DNA displays two migratory waves through Eurasia

Neandertal DNA discovered in cave mud shows that two groups of ancient humans migrated through Eurasia.
Researchers note in Science on April 15 that genetic material from three caves in two countries shows that an early generation of Neandertals about 135,000 years ago could have been replaced by genetically and possibly anatomically distinct descendants 30,000 years later. The pacing of the second wave shows that it could be related to temperature and environmental changes.
“The people who have remained in a cave will take human DNA without tracking our bodies, and curious items on certain people from that DNA can be found,” the researcher says.

According to Benjamin Vermont, a population geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, “we can get human DNA from people who lived in a cave without having to search their bones, and we can discover fascinating things about those people from that DNA.”

Scientists demonstrated a few years ago that ancient human DNA can be extracted from soil, which includes genetic material left behind by our forefathers in the form of skin flakes, saliva, dried excrement, or bodily fluids such as sweat or blood. As a result, genetic studies of ancient sediments may provide useful information about human evolution.

Until now, ancient human DNA found in sediments originated from mitochondria, the organelles that serve as energy factories in our bodies, rather than chromosomes, which hold the genetic instructions for constructing and controlling the body. Even though chromosomes contain much more detail, retrieving samples of nuclear DNA from caves proved difficult due to its scarcity. For any group of chromosomes in a human organism, there are thousands of copies of the mitochondrial genome, and the vast majority of DNA contained in ancient soil belongs to other organisms and microbes.

Vernon and colleagues identified regions in chromosomes rich in mutations unique to hominids to aid the team to to flush out nonhuman DNA while extracting ancient human chromosomal DNA from caves. This allowed the researchers to successfully analyse Neanderthal chromosomal DNA from more than 150 samples of sediment from a cave in Spain and two caves in Siberia dating from 50,000 to 200,000 years ago.

The results indicated that all of these Neanderthals were broken into two genetically distinct waves that spread across Eurasia after the team matched their data with DNA previously obtained from Neanderthal fossils of around the same age. About 135,000 years ago, one appeared.

The researchers discovered genetic traces of both groups in the Spanish cave, with the latter wave seemingly replacing the earlier one. “There were hints of this turnover dependent on mitochondrial DNA, but seeing it specifically with nuclear DNA is very exciting,” says paleo geneticist Qiaomei Fu of Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology, who was not involved in the research.

According to the researchers, the later wave may be attributed to the appearance of the last “classic” stage of Neandertal anatomy, which includes skeletal characteristics including a bulge at the back of the skull that may signify heavy neck muscles or swollen brain regions related to vision.

This thesis stresses the importance of not throwing away soil while operating at possible Neandertal sites, according to paleogeneticist Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona, who was not involved in the study. Special procedures, he says, could be needed to prevent contaminating these areas with modern DNA.