Why does evolution have no good reason to extend our lifespans any longer than they are now?
Answered by: Claire Jordan,worked at National Health Service
In a state of nature humans would usually have died by about 35.
The mechanism of evolution is that the more you pass on your genes to the next generation, the more common your genes will become, so that if you are especially good at passing on your genes the population will gradually become more like you.
Let’s say you are a rabbit. You are a prey species, and will almost certainly have been killed and eaten by something before you are three. If you are going to be dead before your third birthday, how does it improve your chances of passing on your genes to have the *potential* to live to 20? There’s no selection pressure to increase a species’ maximum lifespan much past its modal lifespan.
We can see this demonstrated by the naked mole rat. Naked mole rats spend almost their entire lives underground and so are strongly protected from most dangers. Because of this, a longer potential lifespan does actual translate to a longer actual lifespan in which they have more chances to breed, so selection pressure for them does favour a longer life, and they live ten times as long as most rats of their size.