Expert: Dr. Jeffery Raymond - 10/3/2011

Question
QUESTION: Dear Dr Jeffery

I want to know the fundamental base reason for why Maximum
Life span of Animals, Fishes,  Birds vary or differ ?

i.e.

Cat living up to maximum 18 years
Dog living up to maximum 22 years.
Human Being up to maximum 130 years

i.e why the maximum life span varies from Horse, Tortoise, Cat,
Crocodile, Parrot, Whale ?

is it because of cell, hormone, gene, blood etc ?

i would like to know the fundamental reason for this in terms of Biology ?.

Thanks & Regards,
Prashant S Akerkar

ANSWER: There are "age markers" at the end of chromosomes that are clipped every time a cell divides.  This means that the more a cell divides, the sooner it runs out of "age markers" (telomeres).  While not all species have the same number, a good rule is to assume that they do and then look at the metabolism of the species.  The higher the metabolism, the more cell splitting occurs and the sooner the markers run out.  Once the markers run out in a given cell, it will no longer divide.. when this first starts to happen we call it maturity, when a lot of cells wont divide we call it old age.

As for the biological imperative for this, basically mother nature needs three things out of a species:  It needs to make babies (often a couple times), it needs to stick around long enough to make sure the babies live, and then it needs to die so that the next generation is not competing with it for resources...  Only by making room for the next generation will the processes of evolution and natural selection be able to take their full cycle. Effectively it is important that the old models make room for the new so the new can see if they do any better.  

I hope this helps.

---------- FOLLOW-UP ----------

QUESTION: Dear Dr Jeffery

Thank you.

But why the maximum life span varies from Horse, Tortoise, Cat,
Crocodile, Parrot, Whale, Human Being ?

i.e.

Animals living on Land i.e Human Being, Cat, Dog, Horse, Elephant
Animals living in Water i.e. Fish
Animals living in Land and Water i.e Amphibians
Birds on Air and Land

Thanks & Regards,
Prashant S Akerkar

Answer
You will need to look up the gestation period, time to maturity and metabolism info (heart rate is a good measure).  All of these are a strong indication of which species are designed to "last" longer as all of them represent how fast cells develop and split.

Examples:
Fast gestation period means rapid growth during early phase of life... points at shorter life time.
Fast transition to maturity means rapid growth during development to an adult that breeds... points at a shorter life time.
Fast heart rate means fast metabolism means rapid cell replacement... points at a shorter life time.

In a general sense, the importance of these factors fall in to the following trend:
Metabolism > Gestation >> Maturation

I hope this helps.