What determines an organisms lifespan?



I’ve tried looking this up on my own – and the only real answer I seem to get is “how large the animal is”

The internet says *the smaller the animal, the shorter the lifespan*

However, this leaves me with more question….

Why do humans average 70-90 years, but giraffes average 26 years, blue whales average 80-90 years, **and the giant tortoise which is smaller than all of them averages 150 years** ???

In: Biology

It has to do with metabolism, evolution, and predation. _In general_:

•the slower an organism’s metabolism, the longer it lives. This is mostly because organisms release cancer causing chemicals (like oxygen free radicals) as part of their metabolism, and because their cells wear out faster

•evolutionarily, organisms that care for their young live longer. If they didn’t, fewer young would survive and they would be selected against. This seems to be part of the reason people live so long once they make it through childhood.

•predation means that some animals are evolutionarily selected to live fast and die young. Because evolution has selected them to procreate early, they don’t have genetic defenses against aging.

Size correlates with metabolism in mammals, so that’s what you’re probably thinking of. Predation is why bats live about 10x longer than mice, even in captivity. And R vs S selection is why apes live longer in general than other mammals.

Edit: of course, there’s some imbalance now due to medicine.