Question:
Is there any hypothesis about senecense?
Replies:
YES, there are several. If you want the straight poop, read the
review article in Nature volume 262, March 25 1993, pp. 305-311 by L.
Partridge and N. H. Barton. I will tell you what little I know of this topic.
There are two major types of hypotheses: adaptive and maladaptive. The
maladaptive hypotheses basically state that ageing is the unavoidable
consequence of living in a harsh environments amongst insults like radiation
that can destroy your genes and cells. It is hard to believe that this is the
whole picture as different life forms lives different amounts of time
(thousands of years for some trees, and clonally reproducing fungi), but one
can still save the hypothesis by claiming that certain organisms are better at
protecting themselves from the environment. The other type of hypothesis is
an "adaptive" one in that it claims that it is senescence is a better way to
reproduce one's genes that by trying to live forever. It basically says that
if you have one gene that helps the organism to reproduce early and die early,
that gene will out reproduce one that reproduces late and dies late.
Therefore it is beneficial (reproductively) to have genes that help you
reproduce early and often, even if that means that they will have deleterious
effects on your life later. Kind of stealing from peter to pay paul. A
correlate of this is that organisms that reproduce only once tend to die soon
thereafter, and those that reproduce many times seem to last longer. The
answer to senescence could be a combination of these two hypotheses. Much of
this work is theoretical and a satisfactory answer has not yet been obtained.
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