Dave Slayer said:
coelacanth said:
[quote="Dave Slayer":2ssmwc79]Can natural selection turn a squirel into a donkey?
:crazy
If this is serious, I will answer you, but I get the sense that you are not being serious.
I would seriously like to hear your answer. :yes[/quote:2ssmwc79]
You may want to grab a cup of coffee ;)
First, to clarify, it would have to be a population of many squirrels that you begin with rather than a single squirrel. Second, it should be pointed out that the word “squirrel†refers to almost 280 species of rodents in the family Sciuridae.
To say “squirrel†and “donkey†is to recognize them as species. Let’s then take one species of squirrel, the Eastern Gray Squirrel. The most commonly used definition for this type of context would be the biological species definition, which defines a species as a group of organisms that are so closely related to each other that they can breed and produce fertile offspring. Using this definition, you would be asking if natural processes (unguided by man; not artificial selection) would ever turn a squirrel population into creatures that were able to interbreed with donkeys. This is so absurdly and highly improbable that it is laughable, requiring an enormous amount of just the right mutations and selective pressure as to eliminate both pre-zygotic and post-zygotic barriers to breeding (in other words you would have to make it so that nothing stopped fertilization beforehand and also that fertilization resulted in the development of a viable, fertile adult). In order for this to happen, their genomes, both I presume in the neighborhood of 3 billion base pairs, would have to be remarkably similar, while right now there are radical differences despite the many similarities. Even if mutations occurred that made the Eastern Gray Squirrel evolve to appear similar to a donkey, the odds of all the necessary changes occurring at the genetic level in a way that would make them compatible is so mind-bogglingly infinitesimal that we can rightly approximate it to be zero. Therefore, if pressed to answer to your initial question in one word, I would say “no†rather than “improbable†because “improbable†doesn’t even begin to convey how unlikely that scenario would be if we give proper attention to the definitions. Evolution tends towards diversity, and once species have diverged to the extent that squirrels and donkeys have, they really do not merge again into one.
To watch and see if they become something that sort of
resembles a donkey would be a different story, but also be extremely unlikely and take eons. However, many of the basic components are there. Determining if the resemblance was close enough would really be subjective. It would be a lot more likely if squirrels survived a mass extinction that killed all the large mammals on earth except for an isolated place where donkeys remained unchanged for the eons necessary for the changes to occur within the squirrel population. That way, there would be lots of niches available for adaptive radiation. For it to happen, it would certainly have to occur in an environment where no donkeys already existed due to competitive exclusion. There is no ultimate “end product†of evolution known as a “donkeyâ€Â, but rather that is a term that we use to describe what we see currently; in a sense everything is in a state of transition. No matter where the future evolution of squirrels takes them, genetic drift is bound to play a strong role alongside natural selection in any future changes. In short, to the idea of them evolving into something that resembles a donkey: highly improbable, but possible I suppose.
The scale of the type of change you are talking about - squirrel to donkey – is a correct understanding of macroevolution, as pointed out by John’s reference to the idea of artiodactyl (Pakicetus) ancestry of whales (not actually cows), common ancestry between humans and other living apes, etc. Large changes like this are inevitable over millions of years, but any particular large-scale change with predefined start and end points is highly unlikely.
I hope it was not a waste of time for me to type this out…