Programmed Aging

The maximal lifespan of a creature is under some form of genetic control, as is evident from the characteristic lifespans associated with each species.  Laboratory mice live on average approximately 2 years in captivity.  Indoor cats live about 14 years, horses live about 30 years, and humans (in the United States) live about 80 years.  This length of time is a signature specific to each species, and like all other signature traits it must be a consequence of genetic makeup.  Lifespan is at least partially genetic – check.  The question then becomes: which genetic elements are the most responsible determining lifespan, and why?  One immediate theory that often arises from the genetic aspect of lifespan is that all aging organisms harbor “suicide genes.”  In other words, genes that have been selected by evolution specifically because they kill the organism after a certain length of time.  Theories of suicide genes often include the idea that aging has evolved as a means to benefit offspring by selectively removing older individuals from a population, thus freeing resources such as food from increased competition.  (The argument for removing older, as opposed to younger individuals can be made assuming that older individuals potentially harbor more time-dependent DNA mutations and macromolecular damage that would limit their potential to produce fit offspring.)  I would like to make a short argument against this theory based on a few predictions.  (1) Genes that specifically removed an individual for the good of its offspring would have difficulty becoming the dominant allele in a population since they would confer the same benefit to all members of the population, while at the same time removing members of the population that specifically harbored that allele.  (2)  Environments with geographically-limited resources, such as islands, should have a higher number of species with comparatively short lifespans than environments with less competition for resources, which as far as I can determine from the literature is not the case.


Leave a Reply

Your email address will not be published. Required fields are marked *