Why in so many cases does it seem like the larger an animal is, the older is average lifespan is? Some bugs can live for days or weeks, but humans and sea turtles can be over 100 years old?
In: Biology
Not an expert at all but I believe metabolism plays a big factor in it all.
Metabolism also in general plays a big factor in reaction time, think of how a fly can dodge you swatting at it repeatedly. From the fly’s perspective you’re actually very slow, it’s body is working at a much higher rate and leading to a shorter life.
I would like to Introduce you to the hydra, a small aquatic animal that seems to live basically forever
Not a specialist, but it depends. But, basically, if the animal is simple (not many types of cells), then it survives because… It’s simple. Examples: sponges and some jellyfish. If it is complex, then the smaller the animal, the easier it loses heat, and therefore, the higher its metabolism. Higher metabolism means more oxidation, which means more cell and DNA damage, which causes age (or cancer) and eventually leads to death. The opposite works for bigger animals, which basically have slower metabolism, but as they have huge number of cells, one would expect them to be infested with cancer: more cells, more replication, more cancer, then death. I think it’s not well understood how, but it’s generally agreed that they have mechanisms to prevent cancer and so they live longer, because they have slower metabolism and less cancer.
Another interesting aspect is that although, generally speaking, the larger the animal, the longer the life span, the smaller the breed of the animal, the longer the life span.
I saw a recent study that said every living thing gets a billion heart beats. Some burn through it faster than others. This makes the metabolism comment correct also.
The relationship between age and size is not as self-evident as you might think. There are some bugs that can in fact live to be decades old (Termite queens and some cicadas). Many birds, although not very large have some of the longest lifespans in the animal kingdom (Parrots can live to 80 years, although they generaly have a very high metabolism). Whales and Elephants are much larger mammals than humans but they do not have longer lifespans (although they might if they were given the same medical care). Ageing is a very complex topic that is still very poorly understood by scientists. It is a number of factors that result in the variety of lifespans in the animal kingdom and while metabolism, cancer rates, and the like play important roles, environmental factors, like the risk of being killed by predators are also important. Consider also that getting to a very old age is only selected for in evolution if it means an increase in reproductive sucess. Most animals die quickly after they stop being able to reproduce.
Slower metabolism. When cells burn oxygen and split, they degenerate. That’s aging. The bigger the animal, the slower this process goes. But it also means they can’t move that fast for too long. Unlike humans who are designed to run for hours in their primal form.
Check out the book Scale by Geoffrey West. There is actually correlation between an animals size and the metabolic rate that leads to animals like hummingbirds and blue whales having roughly the same number of heartbeats over the course of their lifetimes.
Here’s a summary:
https://link.medium.com/gbEjB14peib
Latest Answers