However, I will say that in at least one of the examples you cite, the isolation of populations is claimed to have occurred thousands of years ago. How do you know?
By analyzing and comparing their DNA. When appropriate fossils are available, those can be used as additional confirmation.
Isn't it possible that there were multiple species all along?
Again, common ancestry leaves clear signs in the DNA.
And why is it that we never hear of a beneficial mutation in humans that actually improves our performance?
Maybe you're not reading the right journals. Here are some examples:
Dean, M. et al., 1996. Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Science 273: 1856-1862And my favorite:A mutation in humans which increases resistance to AIDS. Excerpt from abstract: "The CKR5 structural gene was mapped to human chromosome 3p21, and a 32-base pair deletion allele (CKR5Delta32) was identified that is present at a frequency of approximately0.10 in the Caucasian population of the United States. An examination of 1955 patients included among six well-characterized acquired immunodeficiency syndrome (AIDS) cohort studies revealed that 17 deletion homozygotes occurred exclusively among 612 exposed HIV-1 antibody-negative individuals (2.8 percent) and not at all in 1343 HIV-1-infected individuals."Weisgraber KH, Rall Jr SC, Bersot TP, Mahley RW, Franceschini G, Sirtori CR, 1983. Apolipoprotein A-I Milano. Detection of normal A-I in affected subjects and evidence for a cysteine for arginine substitution in the variant A-I [PDF file]. J Biol Chem 258: 2508-2513.A mutation in humans which provides increased protection from arteriosclerosisheart attack, and stroke. Also see: Apolipoprotein AI Mutations and Information.
Boyden, Ann M., Junhao Mao, Joseph Belsky, Lyle Mitzner, Anita Farhi, Mary A. Mitnick, Dianqing Wu, Karl Insogna, and Richard P. Lifton, 2002. High Bone Density Due to a Mutation in LDL-Receptor–Related Protein 5 New England Journal of Medicine 346: 1513-1521, May 16, 2002.Here's part of an article about the mutation:A mutation in humans which results in extremely strong, dense bones. From the abstract: "Genetic analysis revealed linkage of the syndrome to chromosome 11q12–13 (odds of linkage, >1 million to 1), an interval that contains LRP5. Affected members of the kindred had a mutation in this gene, with valine substituted for glycine at codon 171 (LRP5V171)."
And here's a grab-bag of beneficial human mutations: Examples of Beneficial Mutations in Humans .By identifying a genetic mutation that causes extremely high bone density in people, Yale researchers have found a potential target for the prevention or treatment of osteoporosis, it was reported Thursday in the New England Journal of Medicine.
The finding was made when the senior investigators, Richard Lifton, M.D., chair of the Department of Genetics at Yale School of Medicine, and Karl Insogna, M.D., professor of internal medicine and director of the Yale Bone Center, identified a Connecticut family with bones so strong they rival a character in the recent movie, "Unbreakable." Osteoporosis is a loss of bony tissue that leads to fragile bones.
"If there are living counterparts to the character in ‘Unbreakable,’ who is in a terrible train wreck and walks away without a single broken bone, it’s members of this family," Lifton said. "They have extraordinarily dense bones and there is no history of fractures. You find this maybe once in a million people."
Lifton said those family members with the genetic mutation have no symptoms. They do have a strikingly deep and wide jaw and bony growth on the palate. They also report trouble staying afloat when swimming.
From everything I observe around me, if someone is born with a genetic aberration so severe that it precludes them from breeding with regular humans, first they would have to survive. Second, it would have to be beneficial to be considered evolutionary progress. Third, they would have to find a mate with exactly the same genetic mutation to generate a new population.
Uhh.. You've got a few misconceptions here.
First, evolution is not a matter of mutations that are "so severe that it precludes them from breeding with regular humans". Mutations which don't prevent interbreeding are evolution as well.
Second, evolution is not just "beneficial" mutations. It includes neutral mutations as well, and also the detrimental mutations which manage to get a foothold in a population. And "beneficial/neutral/detrimental" is not an absolute measure -- a given mutation can be any of the three depending on the particular context. For example, the sickle-cell allele is a net benefit in populations which are frequently exposed to malaria (heterozygous individuals are more resistant to malaria), but a net detriment in populations which are not (because homozygous individuals often die without modern medical attention).
But the biggest misconception is in this sentence: "they would have to find a mate with exactly the same genetic mutation to generate a new population."
No, they wouldn't. Speciation does not reach the point of precluding interbreeding between the "parent" and "daughter" populations via one "really big" mutation in a single individual which suddenly prevents it from mating with any of its cousins in the population as a whole.
Instead, it occurs via the accumulation (across generations) within a subpopulation of *many* mutations, none of which is by itself "big enough" to preclude interbreeding with the original population.
Let me show one example scenario (out of many) to show how it can work. Consider a population of species "X". At some point in time the population gets divided into two separated populations, perhaps by a forest fire in the middle of its range, or a few herds migrating to a distant food source, or whatever.
Because these populations are not actively interbreeding (even though they *could*), mutations which occur in one subpopulation (call it "X1") stay within population X1, and never make it into the gene pool of the other subpopulation, "X2". And likewise for mutations which occur in individuals in X2.
None of the mutations are large enough to prevent the first individual in which the mutation occurred from mating with any other member of its subpopulation. Most mutations *don't* result in such "instant infertility" issues. And the few that do would clearly cause the individual who gets it to be "sterile" (by definition), and it would die with that individual instead of being passed on. It be flushed immediately out of the gene pool.
And no, there's no problem with various mutations being passed around a population willy-nilly -- that's what alleles are all about. That's what alleles *are*.
And due to selection, genetic drift, and other processes, many of the new mutations will "fix" in the population (i.e., become the *only* allele in the population at that gene locus, after having displaced its "competitor" alleles).
So over time, population X1 accumulates its own unique set of changed alleles, while X2 accumulates a *different* unique set of changed alleles. Each new allele was not enough to prevent interbreeding *within* the subpopulation it was in. And at the time that allele "fixed", it became a defining part of that subpopulation, and no longer a factor which might cause even small interbreeding difficulties in that population, because now *all* the individuals in that subpopulation have it.
However, eventually you'll find that individuals in X1 and X2 can no longer interbreed WITH INDIVIDUALS FROM THE *OTHER* subpopulation, because each subpopulation has accumulated *enough* small mutations that the total "genetic difference" between the two subpopulations *has* become too great to allow interbreeding with each *other*, even though they can still interbreed *among themselves*.
Remember, *populations* evolve, *individuals* don't. Evolution is change *across* generations.
So now I hope it's clear how one species can split into two, without ever having a point where a single individual was unable to successfully mate with others of its own kind. The key is that subpopulations drift apart from each *other* -- individuals don't drift away from their *own* subpopulation (at least not in big leaps; and when they do change they subsequently "bring along" their own subpopulations by passing their genes to subsequent generations).
If this is true -- and it is -- one would expect to find separate breeding populations in the world at large at different stages in this "drifting apart". And we do.
Dachshunds and Great Danes (as groups) have accumulated noticeable amounts of genetic differences between them (thus the big difference in their appearances and behaviors), and yet they are still genetically "close" enough to interbreed and produce fertile offspring which combine some of the genes of both ("mutts"). At least I *think* they can interbreed... Part of the "genetic difference" which can interfere with interbreeding is "mechanical" mismatches like the huge size difference between these two breeds, which might make mating or childbirth awkward at best, or even unsuccessful.
There are also groups which have accumulated a larger amount of genetic difference between them, which makes interbreeding possible but often unsuccessful (lower fertility rates, etc.) Examples include many cat hybrids, like lions bred with tigers. They *can* interbreed and produce fertile offspring, but quite often the result is instead lack of conception or infant mortality or infertile offspring.
Then there are groups which have accumulated even more genetic difference, and can mate and often produce offspring, but the offspring are invariably sterile. The donkey/horse hybrid, which produces sterile mules, is a classic example.
And finally there are groups which have accumulated so much genetic difference that mating between them has no chance of producing offspring, such as dogs versus cats, for example -- or humans versus lobsters, if you *really* want to get extreme...
And no, two groups don't have to be 100% unable to produce offspring at all even through forced matings, in order to be considered separate species. Reproductive *separation*, by whatever means, is enough. This can include but is not limited to reduced fertility, lack of mate recognition, separated prefered habitats, etc.
Once two subpopulations have ceased interbreeding (or even just curtailed it), for whatever reasons, they're on the road towards drifting apart genetically over time. They're no longer genetically "tied" to each other.
Just some logic that makes it a little far-fetched for me in practice.
I hope I have made a bit clearer how evolution -- as it *actually* works -- does not suffer from the logical difficulties that you originally thought it does.
You evolutionist guys have a real problem. Your teaching methods, as I have been exposed to them in the past, suck! What you say certainly makes sense, and while I do understand that mutations occur all the time, I was unclear on the possibilities that you outlined. On the surface, it seems plausible, but I will withhold judgment personally, because there are others more capable than myself to challenge it.
The 'good' news, ovrtaxt says sarcastically, is that true Christianity is being taught about as effectively in America, if "christian" television is any indication. haha
Thanks for the info, really. I still believe exactly what the Bible says, because Jesus has never lied to me yet, and I speak with Him all the time.
But assuming that your info is also true, and they can coexist with no contradiction, it doesn't challenge my faith in the least. God never said that species don't mutate. If that's how He set it up, cool.
Science is a wonderful thing, truly understood, and scientists owe a debt of gratitude to Christianity for injecting intellectual honesty into a largely superstitious and fearful religious worldview 2000 years ago-- the religious control freaks in the dark ages notwithstanding.
By the same token, Christianity owes a debt of gratitude to science, because without guys like Copernicus and Galileo, where would we get guys like Tyndale and Luther? Or Columbus? Same spirit of challenging the artificial order of man in the name of God.
Thanks for your response. I understand what you are trying to convey. However, it seems that what you are describing would result in a loose definition of species (matter of fact, you used the word 'subpopulations'). X1 and X2 wouldn't be that much different from another, would they? It seems to me that it would take the success of a 'cataclysmic' mutation, if you will, to make the two so distinct as to be noticeably different. Going from a pool of chemicals and information to "us" would require it (many 'cataclysmic' mutations). You would also need a *lot* of time for each 'jump'. Based upon the DNA evidence, some of the "transitions" occurred in a very short amount of time. Not over vast amounts of time as Darwin believed.