"Varying life spans of different life forms"

Gordon D. Pusch gdpusch at NO.xnet.SPAM.com
Fri May 31 20:07:42 EST 2002

vkchn at hotmail.com (Vijay) writes:

> I am looking for information on "why life spans are so varying amongst
> various life forms"
> while there are some animals whose life spans days, there are others who
> have average life spans of years.
> And, the oldest living tree is I believe 4000+ years old.
> How is this possible. what is that determines this. What is the research
> and information available on this aspect as of today.

For sexually reproducing diploid organisms in which ``crossover'' occurs,
there is no particular evolutionary advantage for an organism to survive
longer than about one generation. Greater genetic diversity results if an
organism dies not too much after it should have managed to reproduce at
least once, since if it hangs around longer, it is merely contributing
the same set of genes to the gene pool, whereas if it is replaced by an
offspring, the gene pool will be ``shuffled'' more rapidly.

I don't know much about the reproducive ccyle of trees, but IIRC, most 
of the long-lived species are conifers rather than deciduous trees,
which may perhaps make a difference. Also, unlike animals, plants cannot
move, so they will be exposed to the same genes from their neighbors time
and time again; perhaps this removes some of the evolutionary pressure to
``die and get out of the way.''

Finally, while there is no known biological basis for this factoid, it is
interesting to note that while the average lifespan of the various mammalian
species varies widely, the number of times their hearts beat during that
average lifetime is about the same order of magnitude: roughly 1/3 to 3 billion
(0.3--3 x 10^9). So perhaps in part it is simply a function of wear and tear ---
or as Indiana Jones put it, ``It's not the years --- it's the milage...'' :-I

-- Gordon D. Pusch   

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