There is no known barrier to the tree of life evolving from a single common ancestral species. Evolution occurs in all living populations at all times. There is no known way to stop it short of an extinction event. At no time does it reach a point where no more evolving can occur.
1) Direct experimental evidence. Ex.: even under lab-controlled conditions, basically providing an environment conducive to evolution, untold numbers of experiments performed on Drosophila melanogaster, didn’t alter it, one iota! Not beneficially, anyways! (Poor flies.)
2) Apoptosis. Any mutation in a cell's structure not immediately resulting in a function, like in the irreducibly-complex eye, would have caused cellular self-destruction.
3) Sexual selection. Females are picky! (No further explanation needed!)
None of these offers a mechanism for preventing what creationists call microevolution. You might as well add genetic mozaicism and egg laying, or any other phrase from biology that you can name. They also do not demonstrate what would stop this process, which is why that claim that such a barrier exists is disregarded by the scientific community.
Some processes do have natural barriers. They are called self-limited. Hemorrhaging would be one. There is a barrier that prevents you from extending a hemorrhage of 20cc of blood in 2 seconds to one of 10,000cc in 1,000 seconds. If nothing else, you would run out of blood before that happened.
Or the formation of an icicle on your roof's eave, which is limited by a variety of factors, including there being only a fixed distance for the icicle to grow before reaching the ground, or it falling to the ground under its own weight, or the spring thaw.
But evolution has no such known barrier, just like the orbit of Pluto, which we have been observing for fewer years than it takes for Pluto to orbit the sun. We expect that Pluto will complete this orbit and as many more as is possible for as long as the sun and Pluto both exist in the same solar system.
I'll bet that if there were scripture that said that Pluto will turn around after half an orbit, then do it again a half orbit later, and thus never complete an orbit, we would now be hearing that micro-orbiting - less than a complete trip around the sun - is possible, but macro-orbiting has never been observed, and therefore cannot happen.
Somebody might ask what barrier is there to completing an orbit, and the answer might be a few astronomical terms that offer no mechanism for stopping a planet and reversing its direction. You know, like (1) precession of the equinoxes, (2) variable axial tilt, and (3) anomalous retrograde motion.
But thanks for offering an answer. You counterpart didn't try.
Maybe you'd like to try your hand at the two other questions she evaded:
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Why we would trade in a theory that unifies mountains of data from a multitude of sources, accurately makes predictions about what can and cannot be found in nature, provides a rational mechanism for evolution consistent with the known actions of nature, accounts for both the commonality of all life as well as biodiversity, and has had practical applications that have improved the human condition in areas like medicine and agriculture for an idea like creationism that can do none of that?"
and
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What are we to do with those mountains of evidence consistent with naturalistic biological evolution if the theory ever were falsified, say by finding the legendary pre-Cambrian rabbit or a partially digested human being in the digestive track of a dinosaur?"
Really? How did this turn out w/ Drosophila melanogaster? Mutations even under controlled conditions were....what? Beneficial? I think you know the answer. Yet, in natural, harsher conditions, you expect better results? To account for the huge numbers of vastly disparate (yet functional) lifeforms.... it’s irrational.
Over geological time, we expect different outcomes than in a laboratory over a few years.
Also, those harsh environments you mention are what drive relatively rapid evolution.
Yes, there is another way....by turning a population into homosexuals.
If that resulted in the complete absence of reproduction, that would constitute an extinction event. It should be considered a lethal mutation, and not an argument against Darwin's theory.
As long as parents are producing offspring, evolution continues.
Which raises a question (in all honesty, with no offense intended to anyone): if evolution is indeed based on the "selfish gene".... why would natural selection 'select' for that trait? It would be killing itself, in the long run. No benefit, there.
That question has been considered at length. You can review any of
these articles that you care to.
Evolution occurs because of the natural processes of genetic variation and natural selection. The genes are not selfish. They have no consciousness, and no intent - no more than rain drops falling to the ground.
