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Age varies vastly even in just the vertebrate world, from the 2 years a rabbit has to the over 170 year old Seychelles giant tortoise, who is still going. Obviously, Lifespan will determine population, cultural views on age and most importantly, the amount of knowledge a person can learn and teach.

Is there a method to figuring out the Lifespan of a species? Perhaps related to their metabolism or their activity levels?

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  • $\begingroup$ You can make your species live as long or as short as you want them to be. It's as you've said, the age variety in our world very accurately shows that regardless of size, age can range from short to long. $\endgroup$ – Aify Sep 18 '16 at 19:52
  • $\begingroup$ How does lifespan correlate to population...? $\endgroup$ – NuWin Sep 18 '16 at 20:13
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    $\begingroup$ @UncleTres actually life span and number of offspring are not related in the manner you seem to think. How many kids does the average Salmon have, compared to the average human? And which one of those species lives longer? There's also the important distinction between lifespan and the portion of lifespan during which a species is able to produce offspring. My grandmother won't be able to have any more children, even she lives to be 800. $\endgroup$ – HopelessN00b Sep 18 '16 at 22:29
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    $\begingroup$ OK, enjoy your trolling, I guess. $\endgroup$ – HopelessN00b Sep 18 '16 at 22:50
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    $\begingroup$ It seems that small animals rarely live the full duration of their lifespan, dieing early due to accidents, disease and predation. Grazing animals would accumulate wear and tear in their teeth, which can result in starvation as time passes. Animals that live longer tend to be larger or have effective defenses against predation. $\endgroup$ – Skye Sep 19 '16 at 12:27
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Life span directly relates to body mass and metabolism. Each creature (I'll attach conditions in a moment) gets about a billion heart beats in its life. For smaller creatures with high metabolism, like sparrows and rabbits, this means a very short lifespan, sometimes only a few years. For larger animals with slower metabolisms, like tortoises and elephants, this means a longer lifespan, sometimes over 100 years. Interestingly, chickens and humans are big exceptions, each of them having double the average number of heartbeats per lifetime.Heartbeat chart

So the question is: How big and how fast? If your species is small and moves rapidly, then their lifespans will probably be in the two-to-five year range. If your species is big and slow, look in the 70-to-120 year range.

With that in mind, remember that age does not the species make. With a shorter life, the individual has a higher rate of living, by which I mean that everything happens faster. A rabbit matures much more quickly than does an elephant, but both have comparable percentages of infancy- the percent of the individual's life that it spends in infancy is comparable betwixt the two. You might have a species that lives only a year, but you can still write a coming-of-age story. Likewise, you might have a species that lives for a century and a half, but you can still cover all its life in one book. The trouble arises when you try to apply human time scales to non-human creatures. Take an extreme example, a species with a lifespan of ten minutes. Within ten minutes, an individual is born, lives, breeds, and dies. You could write a novel about the individual, just as you might about a human. There could be legends of a time, many many generations ago, so long ago that it is almost forgotten, when the world was dark, and there was no light anywhere (night-time) or when all the world was blazing with light (day-time). It all depends on the time scale, which I assume will be on the scale of the species whose lifespan you are trying to calculate. As long as your time scale matches your species lifespan, it really doesn't matter, other than stuff like seasons passing or the landscape changing. It's all about percentages and perceptions.

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1.5 billion heartbeats.

Smaller animals - like a mouse - have faster heartbeats, and have shorter lives. Larger animals - like elephants - have slower heartbeats, and have longer lives.

As a young nerd, I once saw a nature documentary that used that as a rule of thumb for the typical natural life of an animal. Unfortunately I don't recall what documentary this was, so I can't cite a reference for it. There may also a caveat, like it applying to land-mammals only.

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  • $\begingroup$ As little evidence as you cite, this sounds like it's true and makes sense +1 $\endgroup$ – TrEs-2b Sep 18 '16 at 21:39
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    $\begingroup$ Turtles, even smaller ones, live much longer. It is I believe more related to the metabolism of the animal, faster the animal, faster heart beat, shorter lifespan. $\endgroup$ – Cem Kalyoncu Sep 18 '16 at 21:54
  • $\begingroup$ @CemKalyoncu, good point! $\endgroup$ – user6511 Sep 18 '16 at 21:56
  • $\begingroup$ @CemKalyoncu this is easily disproved by bats and naked mole rats. Small animals that can live quite long. As a rule of thumb, the metabolism or heartbeats are OK, but they are not really scientific answer. $\endgroup$ – Colombo Sep 18 '16 at 22:39
  • $\begingroup$ Most stuff about life has exceptions. $\endgroup$ – Cem Kalyoncu Sep 19 '16 at 4:53
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I will look at this from a single aspect. There are other aspects which I cannot comment on. My aspect is adaptability. If the environment is hostile and ever changing, your species should have shorter lifespans to allow rapid evolution. In a more stable environment they can live much longer. Thus if elves are to survive, they should have perfect environment and they should be resistant of virus and bacteria. Otherwise, a virus can wipe out significant portion of the population and re-population would take time and another disaster might completely wipe them out.

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If you want to find out the potential age of a species, you might look to finding out the Hayflick Limit for the species.

This theory determines how many times a cell can replicate before it effectively dies. This ultimate cell age correlates roughly with the lifespan of the species involved.

Obviously, this gives you the lifespan of a species in test-tube conditions and environmental factors have to be taken into consideration - especially in predator/prey scenarios or non-temperate climates.

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