you can't reach the microcosmus of nature my friend.when i say that their time expires i mean that they have not a kinda clock but their body chemistry makes them die.none of the organisms in this planet is living in luck.there are some laws that are behind of saying fit animal.when i say strong i mean animals that have strong gene carry.don't be fooled of fitness,camouflage etc.all these factors are the result of gene expression in the organism.if there is a gene that is not well exressed in the anomal this animal is immediatly vulnerable in any kind of danger including health issues.so you can now imagine that mutations that are caused in an organism may have good or bad results.for example the morph of the leopard snake in the wild is either blotched or stripped.for this wild morph to be presented in nature until today is a real proof that this mutation worked well in nature as the blotched pattern meaning that this morph hadn't bad effect to this species.please i don't have any bad intentions in order to reduce guys but i have the sence that you have open a kind of war to me.i study genetics,physiology etc and have knowledgement that it is based not on my mind.if you would like to snob me because you suspect that i am here to make academic speech you should't because i have not such an intentions.finally the clock has to do with the non balanced body chemistry like in everyother living organism resulting sudden deaths.