Evolution holds that there is a “Survival of the fittest” those [organisms] that for lack of a better term have a few tricks up their sleeve will live to see another day, while others perish.
Starfish and sponges, and I’m willing to bet other animals/plants have the abillity to regenerate. This seems to me to be a nice trick up their sleeve. Why can’t we as humans do this?
True, we could have evolved away from this, we don’t need to regenerate anymore, because we don’t lose that many limbs that often. Yet it would seem that in older times, the loss of limbs would be more frequent, to animals and what not.
It’s likely that no species in our ancestry managed to stumble upon a mutation that allows for massive tissue regeneration. Perhaps there’s a biological factor that prevents the regeneration of complex limbs such as ours from even being feasible.
“Survival of the fittest” doesn’t mean that every good survival tactic will be present in every species.
Your assumptions about what “Survival of the Fittest” means is somewhat off. Organisms don’t evolve specific feature to make them better suited; natural selection operates on the mutations available and in the environment applicable.
It’s also highly likely that the trait of regenerating limbs wouldn’t be possible with more complex organisms for a variety of reasons. It also would cost a lot in terms of energy and trade-offs (such as making arms and legs more similar) that would make it an overall negative in the long run. After all, how many people are/were prevented from reproducing due to loss of limbs who didn’t die from massive blood loss?
You have quite the misconception of how evolution via natural selection is proposed to work, there. “Evoltuion” does not hold that those who survive have any tricks up their proverbial sleeves; rather, natural selection states that, as a result of variation through mutation, those individuals who possess a resulting “edge”, however slight, will be more likely to pass on those slight-edge genes to future generations. How much of an edge a given individual has is determined by the current environment.
As such, regeneration may not provide nearly the edge that, say, avoiding losing a limb in the first place would provide. regeneration is more common in organisms whuich aren’t very good at evading predators, and arare in vertebrates (the only instance I can think of off the top of my head is lizards’ tails – wherein having a re-usable break-away tail can be quite helpful in escaping predators). In the case of humans, there is no practical need for the regeneration of lost limbs that couldn’t be more easily satisfied by not losing the limb in the first place.
At any rate, there probably weren’t a lot of ways in which to lose a limb in the first place in our early years. If you were attacked by something that was capable of tearing off a limb, you were very probably going to bleed to death anyway, so what’s the point in having the ability to regenerate that limb?
As Joe Random mentioned, it is not simply enough that a trait be deemed “useful” for it to evolve. First, it must be possible for the requisite suite of mutations to even occur (not all mutations are possible in every genome), then it must occur, then it must provide the individuals in which it does occur that “edge” which yields a reproductive advantage over their fellows.