Ask A Scientist© Biology Archive

Author:      jing
Text:        Is there any hypothesis about senecense?

Response #:  1 of 1
Author:      Jim Murray
Text:        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.