What is the evolutionary origin

of senescence ?

Senescence is the onset of mortality, which is found in nearly all species. A (very basic) form of mortality is found in even the simplest Archaea .

There are a few plant species that never actually die.

I'd say that senescence is what caused the first organisms to evolve in order to reproduce. Without mortality there would be no need of reprodution, thus no evolution

>>3
like what?

>>3
Underground fungi and some kelp. They form a colony that is really the same genetic individual and it never dies as a whole.

It's kind of like you, really, in that your individual cells die but you remain whole and living ... until small, systemic failures accumulate until a critical collapse of system functions occurs.

The basic idea behind most symptoms of "aging" is that past a certain point, there is not much (or perhaps any) evolutionary advantage for you to keep getting older. You might think it would be nice to live to 200, but if you can't have kids past 40-60 (slightly older for some men), much less raise them, there is no evolutionary advantage.

So suppose one particular mutation gives some small benefit earlier in life, but kills you when you turn 99. Well, that mutation is selected for, much to the chagrin of wannabe centenarians.

There is admittedly more to it than that, but this is a very big part of it, evolutionarily speaking.

>>6

cells die on average after 3 days right? So does that mean your whole eye is replaced after 3 days

>>8
Your entire body is essentially new atoms (new to you, at least) on a cycle of every 7 years.