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Jordi Agustí

Longevity URL: http://www.march.es/conferencias/anteriores/voz.aspx?p1=22525&l=2

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.

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