Looking at our past sometimes pushes us to compare ourselves to our ancestors, to measure the distance that separates us from them, whether on a behavioral level or on a physical level. Multiple research studies have shown that before the generalization of agriculture, humans were very mobile, that is to say they made frequent and/or long journeys in order to exploit their territory for food. and find raw materials to make tools. But could they have run faster or longer than our athletes? How active were they? Can we quantify their efforts?
[Un article de The Conversation écrit par Tony Chevalier – Ingénieur d’étude en paléoanthropologie, Université de Perpignan Via Domitia]
If answering some questions directly is difficult, we can deflect them and ask to what extent the physical activity of prehistoric men and women over hundreds of thousands of years impacted the structure of their bones, particularly those of the legs. The bone, through its adaptation during life, reveals in a certain way the efforts made by an individual: the stronger it becomes, the more important the activity was.
More precisely, we are seeking to know how a “simple” walk, even in very mobile people, could have induced such remarkable bone strengthening in some of our ancestors.
The use of scanners makes it possible to precisely study the internal structure of the bones of current and past humans. It is in the field of geometric analysis of bones that this encounter will take place over time. Properly used, the geometry of bone sections, which integrate internal and external diameters, makes it possible to evaluate the robustness (i.e. reinforcement) and shape of the bones and make the link with the mobility of an individual. . Let's see this in detail.
Physical activity changes bones
Mechanical engineering teaches that the geometric properties of a structure account for the mechanical properties. In fact, the external and internal diameters of the diaphyseal section of a bone make it possible to evaluate its rigidity and resistance. The greater the external diameters and cortical thickness of a bone's diaphysis, the stronger it will be.
When we imagine our skeleton, we are tempted to perceive it as a rigid and stable structure. However, bone is a living material throughout life, which renews itself and adapts to the constraints usually experienced. For example, when we walk, we put pressure on our bones, we bend them and twist them a little. As a result, unlike steel, bone reacts to stress by strengthening or becoming lighter. This adaptation is all the more effective if you are young. The bone will not adapt if a type of stress occurs rarely or if the changes in intensity in our physical activities are too small.
Research carried out on athletes has been invaluable in determining whether variations in the demands on our limbs induce variations in bone structure throughout life.
Since the 1970s, work carried out on the arms of tennis players has shown a high asymmetry in favor of the humerus of the dominant arm, the one which holds the racket. Increasing the diameter of the shaft results in greater robustness for the humerus of the dominant arm, that is to say greater resistance. The bone benefit due to constraints generated by sport can in certain cases even continue for another 30 years after stopping practicing sport.
We now know that regular physical activity will generate recurring stresses on a bone, and that it will adapt by changing its geometry (size and shape). Thus, by going the opposite way, studying the geometry of the leg bones would be a way of telling us about their owner's way of moving. Of course, one must be very careful when making this type of interpretation. For example, beyond the multiple factors that can influence bone structure, the structure observed in a prehistoric adult would partly result from its activity at a young age, at a time when its bone was more responsive to mechanical stimuli.
From the structure of bones to the behavior of Homo heidelbergensis and Homo sapiens old
When we look at the leg bones of ancient human species belonging to the genus Homoit is in particular to understand their mobility: we want to know if they walked a lot (high level of mobility), without however defining a frequency of movement and a daily distance. We also evaluate the type of terrain covered, knowing that flat terrain or terrain with relief will impact the bones differently. The more frequent and intense the walking, the more irregular the terrain, and the more the bones will undergo strong stress and will strengthen.
In 2023, we published our research on the mobility of a 24,000-year-old woman from the Caviglione cave (Liguria, Italy). According to the topography of the place of discovery, this woman Homo sapiens had the possibility of moving on both steep and flat terrain, the sea level being much lower than today. The results showed the very high level of mobility practiced by this woman thanks to her femurs and tibias and the adaptation of her bones to frequent movement in mountainous terrain thanks to her fibulas.
More precisely, we highlighted an extremely high robustness of this woman's fibulas compared to her contemporaries, but also compared to field hockey players, whose practice is characterized by great mobility of the ankle. These results would suggest the presence of very intense prehistoric activity on irregular terrain. This type of terrain involves varied movements of the ankle, and in particular frequent lateral movements of greater amplitude than on flat ground, causing the fibula to support more weight and therefore to strengthen.
At 450,000 years ago, we also observed a very high robustness of human fibulae, associated with a strong stretching of the diaphysis of the tibia (Caune de l'Arago, Tautavel). This argues for a high level of mobility and recurrent travel of Homo heidelbergensis both in the plain and on the reliefs around the Tautavel cave.
Robustness that questions
The strong reinforcements observed in some Homo heidelbergensis And Homo sapiens ancient, both women and men, compared to contemporary confirmed athletes, are very surprising knowing that prehistoric men are above all walkers and that the greatest stresses are exerted on the bones during running.
The naturally higher robustness of a prehistoric individual, that is, genetically acquired, could explain some of the results. By studying the relative robustness of the fibula (which takes into account for each individual the resistance ratio between their fibula and their tibia), we eliminate the influence of this type of genetic factors on our results, starting from the postulate that robustness naturally raised would affect these two bones equally. However, this relationship (fibula versus tibia), crucial for understanding ankle movements, gives one of the most remarkable results for the Caviglione skeleton (24,000 years old). It highlights the very high relative robustness of its fibulas.
All the results argue for a multifactorial influence on bone structure and in particular the significant impact of significant and continuous activity throughout life. A high level of mobility from a very young age, when the bone is particularly reactive to mechanical stimuli, associated with travel in the mountains, or on other irregular terrains, or even with the practice of running, could explain a such robustness in adulthood in individuals who lived between 500,000 and 20,000 years.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
