Why Homo sapiens took 100,000 years in the teeth

Homo sapiens neanderthalensis (reconstruction at the Neanderthal Museum) -

• The discovery of new Homo sapiens bones calls into question the age of the first "modern" humans, according to a study published by our partner The Conversation.

• High resolution scans have allowed a more refined dating of these fossils.

• Analysis of this finding was conducted by Matthew Skinner, Senior Lecturer in Evolutionary Anthropology at the University of Kent.

If the textbooks are to be believed, all modern humans come from a population that lived in East Africa around 200,000 years ago.

This theory is based on elements that could not be more serious: genetic analyzes carried out on humans all over the world and the discovery of human bones between 195,000 and 165,000 years old in Ethiopia.

But just recently, a large scientific team - including myself - discovered new fossil bones and stone tools that challenge this theory.

The study which has just been published in the journal

indeed pushes back the origins of our species of 100,000 years and suggests that the first humans had already occupied most of the African continent.

The Jebel Irhoud site in Morocco, where the fossils were discovered © Shannon McPherron, MPI EVA Leipzig

Men have always sought to understand their origins - whether biological or cultural.

Archaeological excavations and the objects that they allow to discover thus shed light on complex behaviors, such as the manufacture of tools, symbolic practices which consist in burying the dead or even artistic practices.

As for the understanding of our biological origins, it relies on two main sources: fossil bones and teeth.

More recently, the analysis of ancient genetic material - such as DNA - has also enabled important advances.

This major discovery was made at the Moroccan site of Jebel Irhoud, a site known since the 1960s for its wealth of human fossils and particularly sophisticated stone tools.

However, the interpretation of Irhud fossils has long been blurred by uncertainties around their geological age.

In 2004, anthropologists of evolution Jean-Jacques Hublin and Abdelouahed Ben-Ncer initiated a new excavation project there.

They then discovered stone tools and new

fossils

from at least five individuals - mostly pieces of skull, jaw, teeth and bones.

Reconstruction of the oldest

fossil

The dating of fossils

Some stone tools discovered on the Jebel Irhoud site (Morocco) © Mohammed Kamal, MPI EVA Leipzig

In order to date these findings, the team's geochronologists used a thermoluminescence dating method on stone tools found at the site.

By taking into account the level of natural irradiation of the medium in which the tool to be dated has stayed and the nature of the crystals involved, the precise date of the last heating of the sample can be calculated.

So we can measure the accumulated radiation to determine how long the tools have been buried.

This analysis indicated that the tools were about 315,000 years old, to within 34,000 years.

Our “Paleontology” file

The researchers also applied electronic spin resonance, which is a similar technique, but to analyze teeth.

One of the teeth found on the site was thus dated 286,000 years old, with a margin of error of 32,000 years.

All of these analyzes indicate that

- in other words, modern humans - lived in the northwestern quarter of the African continent much earlier than previously believed.

But how can we be sure that these fossils belonged to a member of our species and not to an older ancestor?

To answer this question, the team's anatomists used high-resolution computed tomography (CT scans) to produce detailed digital copies of these precious and fragile fossils.

They then virtually reconstructed the face, skullcap, and lower jaw of all of the specimens found, and using sophisticated measuring techniques, they were able to determine that these fossils had a modern morphology.

We can therefore distinguish them from all the other human species which we know - thanks to their fossils - that they lived in Africa at the same time.

Virtual paleoanthropology makes it possible to correct the deformations and fragmentation of fossils.

High resolution scans have also been used to analyze structures hidden in dental crowns, as well as the size and shape of dental roots hidden in the jaws.

These analyzes, which were the focus of my contribution, revealed a number of dental features similar to those of other modern human fossils.

Although their characteristics are more primitive than those of the teeth of humans today, they are markedly different, for example, from those of

and

.

This discovery and these scientific analyzes confirm the importance of Jebel Irhoud as the oldest site documenting an early stage of the origin of our species.

Our “Prehistory” file

Archeology versus genetics

As a paleoanthropologist who focuses on the study of fossil bones and teeth, I'm often asked why we don't just address these issues using genetic analyzes.

There are two main reasons for this.

While incredible progress has been made in recovering and analyzing genetic material from fossils that are hundreds of thousands of years old, it seems that this type of analysis is only possible under special conditions (and unfortunately rare) burial and fossilization, i.e. low and stable temperature.

This means that there are fossils for which we will never be able to obtain genetic data and therefore we must rely on the analysis of their morphology, as we already do for other very interesting questions related to the early periods of the history of human evolution.

The fossils as they were discovered © Steffen Schatz, MPI EVA Leipzig

Furthermore, understanding the genetic basis of our anatomy only teaches us part of what it means to be human.

Understanding, for example, how behavior over the course of our lives can alter the external and internal structure of hand bones can help reveal how we have used our hands to make tools.

Likewise, measuring the chemical composition and cellular structure of our teeth can reveal what we eat and help understand our development during childhood.

It is these factors that help us truly understand how you and I are both alike and different from the early members of our species.

The pan-African origin of Homo sapiens (Paris press conference on the discovery of Jebel Irhoud, June 7, 2017) © Aline Richard

And of course, we must not forget that it is thanks to archeology that we know when we started to adopt artistic practices, to adorn our bodies with jewels, to make sophisticated tools and to access a varied range. plant and animal resources.

Moreover, some scientists argue that human species prior to

had already adopted some of these incredible behaviors.

Future advances in research will reveal the uniqueness of our history and the evolution of our lineage.

So let's encourage a new generation of young scientists to seek out new fossils and make archaeological discoveries that will help us put together the complete puzzle of human evolution!

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This review was written by Matthew Skinner, Senior Lecturer in Evolutionary Anthropology at the University of Kent.

The original article was translated from English by Sonia Zannad and published on The Conversation website.

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