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Author Topic: What determines the lifespan of an organism?  (Read 2272 times)

Offline chris

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What determines the lifespan of an organism?
« on: 05/09/2014 09:24:11 »
I was asked why a mouse is outlived by an elephant. I ventured that it's to do with metabolic rate and surface-to-volume ratio. The questionner then astutely followed up with "what about birds then?"

So, why do birds appear to live for longer than their body size should dictate? Or do they?

I pointed out that comparing a bird with a mammal is dubious since birds are living dinosaurs separated from mammalian evolution by some 300 million years and, physiologically, the two are quite different.

But what does everyone here think?


 

Offline RD

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Re: What determines the lifespan of an organism?
« Reply #1 on: 05/09/2014 18:46:43 »
Being subject to predation selects for a shorter life-cycle and lifespan  ...

Quote from: sciencefocus.com
... Species with lots of predators canít expect to escape being eaten for more than a few years. So they evolve to reproduce as quickly as possible, and in large numbers. This takes a lot of metabolic resources out of the adults, and they are more likely to die shortly after breeding. Even more importantly, genetic mutations that might cause disability or disease later in life donít have any effect on natural selection because those individuals have already reproduced. This means mutations of this sort tend to accumulate in the species, and so its maximum natural lifespan will tend to shorten.
http://sciencefocus.com
 

Offline CliffordK

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Re: What determines the lifespan of an organism?
« Reply #2 on: 06/09/2014 18:25:47 »
Excellent summary.

So, it all depends on getting to reproductive age, the number of offspring that also reach reproductive age, and the number of reproductive cycles.  Quick to reproductive age with lots of young, and there is little stimulus for the adults to have a long life.  And, there would be environmental pressures for a high mortality rate to prevent overcrowding.

Having a long time to get to reproductive age may indicate a species that has significant learning that is important to their survival, but also longer lifetimes.

Some species of birds or other animals only have one, or perhaps two viable young a year.  That would mean for "replacement", they would need to have babies for at least 2 or 3 years, perhaps more with high infant mortality rates.

Several species have a type of menopause, or "grandmothers" who are no longer reproductively active.  Perhaps the grandmother role is both babysitting, as well as carrying knowledge and helping train the family.  Bait for predators?
 

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Re: What determines the lifespan of an organism?
« Reply #2 on: 06/09/2014 18:25:47 »

 

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