Interspecific competition theory of aging
The theory of aging based on interspecific competition seems to be the least probable at the present time (Nusbaum 1996). According to this theory, it is advantageous for a species if its members age and die and make room for new individuals of the particular species. In this way, the population can gradually evolve to adapt to changing living conditions. A basic drawback of this theory is that it does not take into account the simultaneous opposite action of individual selection. It could be advantageous for a species as a whole if faster and better adaptation of the gene pool of the population to external conditions is facilitated through programmed death of individuals. However, it is advantageous for the individual member of the population if he ages as slowly as possible and lives as long as possible and consequently leaves the greatest number of progeny. Any mutation that causes slowing of ageing in its carrier will increase his individual fitness and will thus have a tendency to increase its frequency in the population and finally become fixed, without regard as to whether its fixation reduces the chance of long-term survival of the entire species.