Commentary on AR Human fossils from the Sima de los Huesos. Forty years of discoveries and research SI: Of ancient and present lifestyles

The present Special Issue “Atapuerca” of The Anatomical Record contains both invaluable new evidence about our ancestors and is, as Ignacio Martínez, one of our fantastic co-guest editors for this Special Issue states, a unique sample of the site with the most fossil remains of the human genre ever in the world, and the one that has contributed the most to understanding the evolution of hominins in the Pleistocene. However, I would like to focus in this Commentary on another transcendental aspect of this volume. Apart from the impressive cultural and academic value of this knowledge, what other uses does this scientific knowledge have? Let's reflect on lifestyles. Our lifestyles. Through ancient lifestyles.

The vast majority of us know who we are. Among other things, because we know who were our parents, grandparents, great-grandparents, and so on, were, we know where we come from and where we are (it remains to be determined where we are going). However, except for very generic data derived from genetic analysis, it is extremely difficult for us to know much further back than a few 100 years. Very few people know their historical life line beyond 200 years; in a few cases, perhaps a few centuries more. Beyond this, nothingness. As a human species, the approach is very similar in theory. However, in practice, it is even more complex. There is a growing body of evidence that the lifestyle of our close ancestors has an epigenetic impact on us. Difficult not to conclude that the lifestyle of our one-million-year old ancestors, being active for hundreds of thousand years, is not going to have a similar, or even greater, impact. And to know where we, as a species, come from, we must analyze the remains that our ancestors have left on the planet. Which is obviously enormously difficult, both because there are very few remains and those that exist are partial or almost completely destroyed, and because the evidence will, in any case, be indirect in terms of the knowledge we want to extract about where we come from. This is the gap that the scientists who have worked in Atapuerca in recent decades come to fill.

Thanks to the scientific evidence obtained in the Burgos sites and the theories developed based on them, we have an idea as surprising as it is continually growing and, therefore, more promising than we could never have suspected just a few decades ago. In this commentary, I am going to raise a simple example of the enormous usefulness that the scientific knowledge of our ancestors has for human culture.

The current lifestyle of humans has been defined numerous times as very harmful for us, exemplified in the health problems derived from our terrible diet, our sedentary lifestyle, and the stress suffered by a huge percentage of the world population. This is understood in the context of a progressive worsening of our diet, our sedentary lifestyle, and our current level of stress compared to that of 300, 400, 500, or even 1000 years ago. Finally, the comparison of such a modern lifestyle with the one that our ancestors could have had is also evaluated. Considering that lifestyle could have determined our evolution (remaining relatively constant for hundreds of thousands of years or, in some cases, millions of years), it could make an enormous difference, capable of generating many of the typical health problems of today's life. But what do we know about the diet, level of physical activity, or stress of Homo erectus, to name just one case?

The scientific evidence that we can evaluate about our ancestors is obtained from four main sources of information: (1) human bones, (2) remains of various kinds found next to the bones or independently (remains of food, bones of other animals, products derived from their behavior, as evidence of fire), (3) products of its manufacture or its direct action (such as the lithic industry, cave painting or footprints), and (4) genetic data obtained from the DNA extracted from some of its fossil bones (to this we will add that lately, stable isotopes of Carbon and Nitrogen are also studied to obtain data on diet).

Specifically, let's look at physical activity. We cannot find direct clues in this entire body of evidence about what our ancestors did or did not move. But, on the contrary, after studying the bone remains, we can determine the capacity or adaptation level of our ancestors to long-distance walking or running. In this sense, we have learned about evolutionary changes useful for the energetic cost of running, such as in the Achilles tendon, the longitudinal arch of the foot, or stride length, the surface area of large joints in relation to body mass, or the robustness of femoral shafts, and the expansion of the sacrum and iliac end of the spine, among many others. Our ancestors were ready for this endurance walking or even running, starting with Homo erectus (although this all does not scientifically certify how much they really moved). Yes, we can conclude without much error, that the genus Homo and especially Homo sapiens, is comparatively very adapted for long-distance walking and running.

As for the direct evidence, and in case anyone wants good news, here it is: in the not-too-distant future, we will be able to find epigenetic molecular evidence in bone remains that will allow us to determine with complete certainty not only what they ate, but how much they ate, how much they moved and ran, as well as their stress levels. As of today, it is very complicated due to the instability of microRNAs, for example. But there will come a time when it will be possible.

What there is no doubt about is that all the knowledge that you will find in the pages of this Special Issue of The Anatomical Record “Atapuerca” is a compendium of scientific evidence and its corresponding hypotheses that perfectly portray what is nowadays known about our ancestors from the fossil record found in recent decades in the Atapuerca sites. From this compilation of scientific findings our heroes of this SI have been able to draw invaluable conclusions about what our ancestors were like and how they behaved.

José Luis Trejo: Conceptualization; writing – original draft; writing – review and editing.