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Jordi Agustí

Longevity, ageing, evolution URL:

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. There is no register of another fossil hominid showing such a pronounced loss of dentition and reshaping of the jaw. The younger Pleistocene individuals found in Bau de l’Aubésier and La Chapelle-aux-Saints always show a much more complete dentition at the time of death. Although it is worth noting that the later are neanderthals, much more evolved, with larger brains, and a more advanced culture. In addition, samples of of non-human primates with such a degradation of the masticatory system are extremely rare. Considering that currently there are no apes in temperate regions like Dmanisi, we can only guess the behavioral consequences in the framework of the bio-cultural data preserved in the site. D3444 and D3900 were recovered from the B1 layer of block 2, which also contained stone artifacts and eight animal bone remains marked with percussion signs made by stone tools, indicating the processing of animal corpses for consumption of meat, which is a common finding in other hominid sites of the Pliocene and Pleistocene. Meat can indeed be the key to the success of these hominids inhabiting high latitudes, especially during winter, and the consumption of soft tissues like marrow or brains, could allow for the survival of individuals with limited masticatory systems. 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 preferently 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.

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