In agreement with the theory of evolution that has been accepted for 100 years, namely darwinism, the persistence of individuals that cannot contribute reproductively to the next generation is an astonishing example of evolutionary inefficiency. Darwinism postulates that the species surviving a long evolutionary process are those that contribute to the following generation with more descendants (which is how genetic heritage disseminates). From this perspective, the persistence of long-lived individuals who cannot further contribute to perpetuating the species has alway been an evolutionary paradox: What are these individuals -male or female- good for once they have surpassed the age of procreation and transmission of their own genetic pool? Particularly, the recent discovery of a very old individual lacking all of its teeth dating from 1.8 million years ago in the Dmanisi site in Georgia, has starkly obliged us to reconsider this issue. In this individual, the spaces housing the roots of the teeth had already been completely absorbed by the bone, implying that he had not been able to chew meat or hard vegetables for a number of years already. Due to the lack of fruit trees in the surroundings of Dmanisi, it is obvious that this elderly individual had to be taken care of by the group to which it belonged,who probably processed the food it consumed.In the framework of the harsh life conditions experienced by hominids at the beginning of the Pleistocene, what is the biological meaning of keeping individuals who could not take care of themselves and had already fulfilled their reproductive role? Whatever it may be, what is clear is that this type of cooperative behavior was already established in hominids two million years ago.
The key to this and other similar cases could maybe lie in incomprehensible processes within the limits of strict individual selection. Indeed, there are a certain number of characters that are not specific to individuals, but are at the general level of the species, and that nevertheless seem to be clearly favored by evolution. Even though they trespass the limits of individuality, these characters favor the survival of individuals from a supra-individual level, from the perspective of the species. This is what has been named "species selection" or "selection at the level of species" (a heterodox variation of darwinism), and usually affects the "life history" of the individual, the characters that fundamentally affect the age of birth, growth, reproduction and death within a population (those called demographic factors, not specific to individuals but to the entire species). The species that tend to show in their life history the existence of long-lived specimens will be better prepared for short-time climatic crisis. This way, the elders are some kind of memory of the system that may occasionally allow for the survival of the entire group in adverse conditions. These strategies have developed preferentially in migrating organisms like birds, elephants, some turtles and dinosaurs, and of course in ourselves, probably during the early scavenger phase of the Homo habilis, when we migrated from Africa towards the rest of the Old World.
The genomic delay is the lag that exists between our genome, which conditions a physiology and psychology selected to survive in the environment in which the human species evolved, and the artificial world created by culture, with an accelerated evolution that prevents from having the corresponding adaptations selected. This causes in many human beings physical and emotional disorders.
Our genome was selected for more than two million years to become adapted to the Pleistocene, the period in which we became humans. The exclusive characters of our species were selected during this period -corresponding to 99% of the history of the genus Homo, and 95% of the history of our species Homo sapiens- along which our ancestors lived as hunters-gatherers. Although there have been some genetic changes since the beginning of agriculture around ten thousand years ago, these have been quite insignificant. From the anatomical, physiological, and emotional point of view, the Homo sapiens is still a hunter-gatherer. The cultural changes have occurred too fast for us to genetically adapt to them. Our genes have been selected to become adapted to an environment that no longer exists, thus, genes that were useful within the ancient environment in which we evolved can now increase the susceptibility to diseases in the developed world. The different life styles of our hunter-gatherer ancestors and the inhabitants of developed societies cannot be more radical. The environment in which we thrived implied intense physical exercise, food poor in saturated fatty acids, sodium, and sugar, slow cultural changes, and life within small groups in which members received emotional support. On the contrary, the members of developed societies usually have a sedentary life, a diet with excessive saturated fats, sodium, and sugar, chronic emotional stress to which we cannot reply with the fight-flee reactions our evolution has taught us, and social and emotional isolation.
This life style has contributed to a high frequency of cardiovascular diseases, obesity, diabetes, and emotional disorders like anxiety and depression, all of which have become an epidemic in developed societies. The changes of life style can cause epigenetic changes: diminishing physical exercise, the excess of fat, or chronic stress can act as inhibitors of the some gene expressions that can ultimately produce the appearance of chronic emotional disorders, like anxiety and depression, or neuroplastic disorders affecting the learning capacity and memory, and an increase of the oxidative neuronal stress. A better understanding of the environment in which we evolved could help us to have a much healthier life without resigning of the benefits of civilization.
The human being began its evolutionary story 65 million years ago with the apparition of the first primates. Millions of years later, the family of great apes appeared (orangutans, gorillas, chimpanzees, and bonobos): our closest living evolutionary relatives. One of the most relevant characteristics of the human species and of the rest of great apes is the high level of sociability. In order to learn more about this trait of our evolutionary history, it is extremely interesting to observe this same aspect in our evolutionary cousins. We share with them a complex social structure and organization, although there are notable differences between one species and the other. From the lonely life of orangutans, we can go to the "harem" groups of gorillas, and to the complex fission-fusion communities of chimpanzees and bonobos.
But, in what do we differ from the great apes? Which are the main similarities that we share with them in regards to our social life? In all of us, males and females have different roles within the group. Like them, we are self-conscious, and have the capacity to assign intentions to others. Both of these aspects are very important for life in society. We live within complex groups where it is necessary to negotiate, exchange, and cooperate with members of the community. We develop within a social dynamic where sometimes it is necessary to cooperate and coordinate with other individuals, and where strategy, leadership, and the exchange of goods and services is present in our everyday life.
But although we share a social nature, the human being has evolved until becoming an ultra-social primate. What does "ultra-social" mean? Where has this trait reflected along the evolution of the human being? Our social abilities not only has fostered our survival in a complex society, but also our intelligence has evolved to allow us living and exchanging knowledge in cultural and technological groups. Thus, evolution has forged our brain and cognition until making us primates characterized above all by the development of a complex social and cultural intelligence.
The Pleistocene sites of the Sierra de Atapuerca (Burgos) have provided extensive samples of fossil remaings belonging to two past species of hominids: Homo antecessor and Homo heidelbergensis.
The remainings of the Homo antecessor have been recovered from the sites in the Sima del Elefante and Gran Dolina, in the Trinchera del Ferrocarril de Atapuerca, and their antiquity is calculated in range of age between 1,3 and 0,8 million years. The species Homo heidelbergensis has been located in the Sima de los Huesos of the karst complex located in the Cueva Mayor, and it maximum antiquity is estimated in 0,6 million years.
While most of the human evolution studies focused in learning the phylogenetic position of the different hominid species in the human evolution tree, the ample collection of hominid fossils from Atapuerca have allowed for a deeper knowledge on the biology of these two extinct "human" species. Particularly the collections of fossils obtained in the Sima de los Huesos add up to 6.500 remains from around thirty individuals, which means around 90 per cent of all the fossils of this European species worldwide.
The brain and mind complexity of the Homo heidelbergensis are reflected in their behavior and technology (Acheulean or Mode 2). Regarding their body size, we can confirm that the encephalization quotient of this species is slightly inferior to ours; nevertheless, Homo heidelbergensis already took care of their deceased and showed mental capabilities like planning and standardization. The pioneer study on the audition of the hominids from Sima de los Huesos has allowed us to demonstrate that the maximum hearing capacity was at the same frequency as in Homo sapiens. This is an indirect proof about the language capacity of this species, a human character that is extremely difficult to prove in extinct species. In the same way, the relationship between the craneal capacity of the newborn and the size of the birth canal, show that the hominids from the Sima de los Huesos probably had less difficulties at birth than the neonates of our species. The discovery of a complete pelvis in the Sima de los Huesos has been a key finding to work in this particular aspect of the biology of the Homo heidelbergensis, as well as to estimate the size and body weights of the species. The evidences of pathologies and the estimation of the ages of death and longevity of the individuals from this species will be further completed with data we will present to the audience.
Regarding the Homo antecessor it is important to analyze the evidences of canibalism obtained from the study of the fossil remains, and the meaning of this particular behavior in the human evolution.
Symbolic consciousness in the Sima de los Huesos of Atapuerca: hearing and origin of language
One of the big problems when studying the evolutionary history of the human beings is the origin of language. From the point of view of Paleontology, and considering that words cannot be fossilized, the aim is knowing when, in what specie, and under which circumstances did the anatomical structures supporting our most usual way of communication -speech- appeared. For this, along the las half century, there have been two different ways to address the problem: one of them focused on the reconstruction of the throat anatomy of the different fossil hominids, while the other focused in the study of intracranial molds. Neither of these ways has obtained convincing results.
A novel line of research has been established by studying the audition patterns (audiograms) of the current and fossil species. The audiograms of most species of platyrrhines (New World monkeys) and catarrhines (Old World monkeys and apes) are characterized by "peaks" of maximum sensibility around 1 and 8 kHz respectively, separated by a range of less sensibility in the "intermediate frequencies" around 2 and 4 kHz. In opposition to the rest of "anthropoids", us humans have our maximum sensibility precisely in the "intermediate frequencies", in which the human voice resonates.
Using computed axial tomographies of the temporal bone region (more than 100 tomographies per individual), it has been possible to digitally reconstruct the cavities of the external and middle ear from five individuals of the Mesopleistocene deposit in the site Sima de los Huesos (Atapuerca Sierra) assigned to the species Homo heidelbergensis. A number of anatomical variables have been measured over these reconstructions, based on which a circuit model reproducing the function of the external and middle ear has been built to test the acoustic filtration of sounds along the external and middle ear. That acoustic filter is the determining factor of the auditive pattern in each species: the position and bandwidth of maximum sensibility. The results obtained are unequivocal and show that the individuals of Sima de los Huesos had an auditory pattern similar to that of the modern human populations (in both, the position of the area of maximum sensibility, and in the magnitude of the bandwidth) and very different from the one of chimpanzees.
Around thirteen thousand years ago a transformation began in some human populations of Western Asia that lead them towards a very complex social, economic, and cultural period. With this in mind, the Neolithic should be studied has a period of development of human societies from the point of view of three realms mentioned: culture, society, and economy. What can we say then from the perspectives addressed here? How does the Theory of Evolution, and the specific human evolution models, explain this phenomenon? Even though any referential work will address a purely historical vision, we are going to propose an alternative: the fight for survival and the quest for solutions to increasingly complex situations.
Along the last phase of the Paleolithic, the human populations perfected their capacity to obtain food and their introduction in the territory due to a higher efficiency in the use of resources. Most probably, these improvements were linked to a demographic growth. With this perspective, the climate change that started thirteen thousand years ago implied a new distribution of resources, causing shortage in some regions and increase in others, obliging for the evolution of new ways to acquire food and producing a certain demographic crisis.
Based on the archaeological remains, it is around this time that in the Near East the cultivation of plants began, like wheat, at the same time that the first intensive predatory hunts over entire herds of gazelles occurred. And although they were still hunters, the agriculture transformed the populations into sedentary. About eleven thousand years ago, the cultivation of rice started the Far East. Initially in dry environments, and later, around eight thousand years ago, they were transformed into the wet cultivation areas that we know today. In the Higher Valleys of the Tigris and Euphrates, located to the east of Anatolia and to the north of Irak, some populations began developing for the first time cattle rising with goats. In Siberia and Japan, several populations spatially separated invented domestic ceramic tools, a revolutionary invention made by communities that were still hunter-gatherers and nomad. While all these transformations were taking place in Asia, in Europe the climate change produced a completely different scenario: huge land and sea spaces were opened to the north of the continent allowing human groups to substitute the hunting of large herbivores with fishing and the collection of seafood.
Considering the global scenario of change, among all, the ones happening all around the Asian territories are the most revolutionary. We call Neolithic to this entire group of transformations, although it took very long until several of them met in a single point. It still took several thousand years to have some of them meet in the Near East, where the first centralized territories evolved, some larger some smaller, sometimes around a single city, and sometimes around a larger area.
From all this, we can conclude that the human groups adapted to the new scenario with revolutionary individual transformations. An ecological crisis triggered them to look for solutions, which latter allowed them to have a demographic growth once complex societies were established. This demographic growth fostered new expansions and the occupation of new regions, producing new economic activities, like in the case of Europe.