Sciences Why Homo sapiens took 100.000 years in the teeth
PALEONTOLOGY Discover, every day, an analysis of our partner The Conversation. Today, anthropologist explains the importance of recent human fossil finds
Published on 10/11/20 at 08:45
- Updated 10/11/20 at 08:45
If the manuals are to be believed, all modern humans come from a population that lived in East Africa about 200.000 years. This theory is based on elements that could not be more serious : genetic analyzes performed on humans around the world and the discovery of ancient human bones from 195.000 at 165.000 years, in Ethiopia.
But very recently, a large scientific team - of which I am a part - discovered new fossil bones and stone tools that challenge this theory. The study which has just been published in the journal Nature 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 found © Shannon McPherron, MPI EVA Leipzig
Men have always sought to understand their origins - whether biological or cultural. Archaeological excavations and the objects they allow to discover thus shed light on complex behaviors, like tool making, symbolic practices which consist in burying the dead or artistic practices. As for understanding our biological origins, it is based on two main sources : fossil bones and teeth. More recently, the analysis of ancient genetic material - such as DNA - has also allowed important advances.
This major discovery was made on the Moroccan site of Jebel Irhoud, a site known for years 1960 for its richness in human fossils and particularly sophisticated stone tools. However, the interpretation of Irhud fossils has long been clouded 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 Homo sapiens fossils from at least five individuals - mostly skull pieces., jaws, teeth and bones.
Reconstruction of the oldest Homo sapiens fossil ever discovered from analysis (microtomography imaging) of the many fossils discovered at Jebel Irhoud.
Some stone tools discovered on the Jebel Irhoud site (Morocco) © Mohammed Kamal, MPI EVA Leipzig
In order to date these discoveries, the team's geochronologists used a thermoluminescence dating method on stone tools found at the site.
Taking into account the level of natural irradiation of the environment where the tool to be dated has stayed and the nature of the crystals involved, we can calculate the exact date of the last heating of the sample.
So we can measure the accumulated radiation to determine how long the tools have been buried. This analysis indicated that the tools had approximately 315.000 years, at 34.000 years close.
The researchers also applied electronic spin resonance, which is a similar technique, but to analyze the teeth. One of the teeth found on the site was thus dated 286.000 years, with a margin of error of 32.000 years. All these analyzes indicate that Homo sapiens - in other words, modern humans - lived in the northwest 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 scan) in order to produce detailed digital copies of these precious and fragile fossils.
They then virtually reconstructed the face, the skull cap and lower jaw of all the specimens found, and thanks to sophisticated measuring techniques, they were able to determine that these fossils had a modern morphology. They can therefore be distinguished from all other human species that we know - thanks to their fossils - that they lived in Africa at the same time..
High resolution scans have also been used to analyze structures hidden in dental crowns, as well as the size and shape of the tooth roots hidden in the jaws. These analyzes, which were at the center 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 clearly different, for example, those of Homo heidelbergensis and Homo neanderthalensis. This discovery and scientific analyzes confirm the importance of Jebel Irhoud as the oldest site documenting an early stage of the origin of our species.
As a paleoanthropologist who focuses on the study of fossil bones and teeth, I am often asked why we do not simply address these issues using genetic analyzes. There are two main reasons for this. Although incredible advances have been made in the recovery and analysis of genetic material from fossils hundreds of thousands of years old, it seems that this type of analysis is only possible under specific conditions (and unfortunately rare) burial and fossilization, namely a 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 with other very interesting questions related to the early periods in the history of human evolution.
In addition, understanding the genetic basis of our anatomy only teaches us part of what it means to be human. Understand, 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 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, the 7 June 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 jewelry, to make sophisticated tools and access a diverse range of plant and animal resources. Moreover, some scientists suggest that human species predating Homo sapiens 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, encourage a new generation of young scientists to search for new fossils and make archaeological discoveries that will help us to compose the complete puzzle of human evolution !
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.
19/12/19 | PALEONTOLOGY
17/09/20 | HOMO SAPIENS
02/10/20 | GENETIC
13/05/20 | DISCOVERY
22/07/20 | ARCHEOLOGY
29/10/19 | ETUDE
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