People lived in the Americas much earlier than previously thought

The history of early humans must be rewritten following the discovery of about 1,900 stone artefacts in a cave in Mexico.

For the past century, archaeologists have generally agreed that humans arrived in the Americas 12,000 to 15,000 years ago, but now this turns out to be quite erroneous.

Instead, new archaeological excavations show that humans arrived in the Americas more than 30,000 years ago. According to one of the contributors to the research, this is nothing short of a “scientific hand grenade”.

“In 2006, one of our genetic studies pushed back the arrival of humans to the Americas from 12,000 to 13,000 years ago, and although there were many criticisms, it is now accepted that the first humans came to the Americas across the Bering Sea between Siberia and North America a little earlier than assumed before. This study again turns these conclusions upside down and pushes back the time of human occupation by a further 15,000 years. Now we will have to see how the scientific community responds to this,” explains Eske Willerslev, Professor and Director, Lundbeck Foundation GeoGenetics Centre, Globe Institute, University of Copenhagen.

The research results have been published in Nature.

Archaeologists discover 1,900 stone artefacts

Researchers and archaeologists from Denmark, Mexico, the United Kingdom, the United States and Brazil investigated some unique discoveries in the Chiquihuite Cave in Zacatecas, Mexico at 2,740 metres above sea level.

The cave floor consists of a 3-metre-thick layer of compacted earth, and the deeper the archaeologists dug, the further back in time they went.

Down through the layers of soil and debris, the industrious archaeologists discovered about 1,900 stone artefacts that ancient humans had left in the cave, including knives, arrowheads and scrapers.

By analysing layer after layer down through the floor using a variety of chemical, physical and genetic methods, the researchers dated the individual archaeological materials and concluded that humans lived in the cave 30,000 years ago. In a wider perspective, this represents a scientific earthquake.

“The discovery is extremely interesting because, at that time, a massive ice cap had not formed over North America, which is why ancient humans could travel from Siberia to North America and migrate throughout the Americas. Later, an ice cap formed, and this only melted sufficiently to enable the crossing again 13,000 years ago,” explains Eske Willerslev.

Other discoveries previously indicated that humans may have occupied both North and South America earlier than 15,000 years ago, but Eske Willerslev says that these discoveries are so debatable that they have not resonated much scientifically.

“However, it makes sense now to revisit the locations where the discoveries have been made, so we can examine the sites a little closer and maybe find more evidence that points in that direction,” he says.

Not ancestors of Native Americans

Another interesting perspective of the new discovery is that it indicates that the people who arrived in the Americas as early as 30,000 years ago were probably not the ancestors of today’s Native Americans.

Eske Willerslev and his colleagues at the University of Copenhagen have previously conducted a genomic study showing that present-day Native Americans emerged about 23,000 years ago. This occurred when Asians mixed their genes with a type of proto-European that no longer exists. The romance took place in Siberia, and only then did this newly formed group of people migrate across the Bering Sea and colonize the Americas from north to south.

This shows that the people who used the artefacts in the Chiquihuite Cave 30,000 years ago cannot be the ancestors of the Native Americans.

Eske Willerslev explains that several other genomic studies by the researchers at the University of Copenhagen indirectly support this conclusion.

“We previously examined some 10,000-year-old bones from Brazil, and they revealed that those people were Native Americans, but also that between 2% and 6% of their DNA originated elsewhere. When we look for living people with the same genes, we find them only in the Andaman Islands between Thailand and India. We have not yet been able to explain how that part of the genome has entered the DNA of the Native Americans. There is no evidence of this in North America, but it paints a picture that the genes from different peoples in the Americas have mixed and that this may already have happened in Mexico 30,000 years ago,” says Eske Willerslev.

Eske Willerslev speculates that when the ancestors of modern Native Americans came to the Americas 15,000 years ago and travelled from north to south, a population already existed in at least South America, and that these two types of humans met and mixed genes.

“Perhaps the Chiquihuite Cave represents this meeting of people,” says Eske Willerslev.

Further evidence required to convince the sceptics

The new study has already been attacked from several quarters, which Eske Willerslev had also expected. According to him, this is always the case when presenting controversial results.

Some researchers wonder whether the tools are human-made at all, and others would like to see more concrete evidence of human activity before feeling convinced that all textbooks about the human colonization of the Earth should be jettisoned.

Based on this, the researchers from the University of Copenhagen have not finished their work in the Chiquihuite Cave either.

The researchers have taken hundreds of soil samples from the cave floor and are investigating these samples for traces of human activity.

A person might have urinated or defecated in the corner of the cave, or the researchers might find scales from the scalp, skin or perhaps a bone or some blood.

If the researchers can find any tiny fragment of genetic material from a human, this could help advance our knowledge about what has happened in American prehistory and who are the ancestors of whom.

The researchers from the University of Copenhagen have recently examined DNA from the Chiquihuite Cave and discovered traces of American black bears, several kinds of bats, sparrows, falcons and various kinds of plants, which have undergone a major change in prevalence as the climate in North America has changed over the past 30,000 years.

“This no easy task, but it is certainly feasible, and we have a reasonable chance of finding something. This is like finding a needle in a haystack, but it is worth a try,” says Eske Willerslev.

“Evidence of human occupation in Mexico around the Last Glacial Maximum” has been published in Nature. The Danish National Research Foundation, Innovation Fund Denmark, Lundbeck Foundation, Novo Nordisk Foundation, Carlsberg Foundation and Villum Foundation funded the study.