Why do all living creatures have such wildly different life expectancies?
In: Biology
On the reproductive side I see that cats can have litters very frequently but live to 20+ but dogs generally live half that? And cats have a faster heart beat than dogs too. It’s very interesting to think they’re on an internal clock.
Basically every living creature only has to live as long as necessary to achieve maturity, find a mate, reproduce and optionally care for its offspring for a while. Reproduction has to be repeated as many times as is required to avoid population decline, taking into account the offspring mortality rate which is normally quite high. Any living time after that is just a free bonus and is not maintained by natural selection. It’s just there. So life expectancy of a species depends on how much time is required for this species (on average) to complete doing all the things above.
Each living being has a set heart beat for generalization sake say 100 heartbeat, so incase of humming bird the heart beats faster lb db lb db gets to that 100 quickly, humans also 100 heartbeat but slower than that of humming bird day lubb. tortoise 100 heartbeats lubbbbbbbbbb dubbbbbbbbbbbb even slower than humans so longest life span than humans probably in 120’s – 150’s.
Under ideal conditions, natural selection would favor animals that live forever and keep reproducing forever. Selection favors animals (or plants) that produce the most successful offspring.
So why don’t things live forever? What we have here is a trade-off. The world is a dangerous place, and keeping yourself alive costs resources. Resources that could be spent on making more offspring. If spending resources to keep yourself alive longer results in more offspring (because you live to breed another day) then great. But if you get eaten by a predator the next day all those saved up resources never get used. Ideally, an animal that is likely to die from environmental causes will want to spend all its resources early on reproduction, causing it to wear out faster and have a lower life expectancy.
In other words, innate life expectancy should be related to the amount of time an animal would expect to survive in the wild before being killed by something. You can see this with many living things. Turtles for example are hard to kill, they carry around strong protection. And turtles have a long innate genetic life expectancy. They reproduce more slowly and move more slowly but make up for it by living longer and having a longer lifetime reproductive output. In contrast, mice are easy to kill. Lots of things eat them, and the average mouse is likely to be snapped up by a bird or snake or cat before it reaches its first birthday. But even if you protect a mouse from all predators, it still has a short life expectancy. It’s entire body is tuned to live fast and breed fast. It just wears out fast, it’s dumping a lot of energy into reproducing and less into maintenance, because there’s no point in trying to take it slow like a turtle…it would just get eaten.
There are other things going on here too, the above explanation is _a bit_ simplified. For example, some animals have structures that are useful but just don’t last forever…mammals can’t really replace or repair adult teeth, for example, and as a result grazing mammal lifespans are limited by how long their teeth last. And some animals just don’t seem to age at all. But it’s a good framework for understanding the question.
Time itself is relative.
In the scope of the life of our universe, all known life forms live for an infinitesimal amount of time.
No discernible difference is present.
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