frako writes:
quote:
What is the fine line that separates micro evolution from macro evolution.
That depends upon if you are asking a biologist or a creationist.
That is, the idea of "microevolution" and "macroevolution" is a creationist construct. It came about because observations of populations showed that the flat out denial of mutations arising and becoming fixed in populations could no longer be denied while retaining any sense of intellectual integrity.
As an example, there is a common experiment that is done in high schools that proves the point:
Take a single E. coli bacterium of K-type. This means the bacterium is susceptible to T4 phage. Let this bacterium reproduce until it forms a lawn. Then, infect the lawn with T4 phage.
What do we expect to happen? That's right, plaques should start to form and, eventually, the entire lawn will die. After all, every single bacterium in the lawn is descended from a single ancestor, so if the ancestor is susceptible, then all the offspring should be susceptible, too.
But what we actually see is that some colonies of bacteria in the lawn are not affected by the phage.
How can this be? Again, the entire lawn is descended from a single ancestor. They should all behave identically. If one is susceptible, then they're all susceptible. If one is immune, then they're all immune. This can't be an example of "adaptation" because if one could do it, they all could do it.
But since there is a discrepancy, we are left with only one conclusion: The bacteria evolved. There must be a genetic difference between the bacteria that are surviving and those that died.
Indeed, we call the new bacteria K-4 because they are immune to T4 phage.
But we're not done. Take a single K-4 bacterium and repeat the process: Let it reproduce to form a lawn and then infect the lawn with T4 phage.
What do we expect to happen? That's right: Absolutely nothing. All of the bacteria are descended from a single ancestor that is immune to T4 phage. Therefore, they all should survive and we shouldn't see any plaques form.
But we do. Plaques do, indeed start to form. How can this be? Again, all the bacteria in the lawn are descended from a single ancestor that was immune to T4 phage, so they should all behave identically. If one is immune, then all are immune. There must be something else going on.
Something evolved, but the question is what. What evolved? Could it be the bacteria experiencing a reversion mutation back to K-type? No, that can't be it. Suppose any given bacteria did revert back to wild. It is surrounded by K-4 type who are immune to T4 phage. As soon as the lawn is infected, those few bacteria will die and immediately be replaced by the offspring of the immune K-4 bacteria. We would never see any plaques forming because the immune bacteria keep filling in any holes that appear.
So if it isn't the bacteria that evolved, it must be the phage. And, indeed, we call the new phage T4h as it has evolved a new host specificity.
There is a similar experiment where you take bacteria that have had their lactose operons removed and they evolve to be able to digest lactose again.
This sort of thing cannot be denied since we can reproduce the effect at will.
So creationinsts came up with the argument of, "But it's still a bacterium!" ignoring that the whole point of the experiment was not to produce a new species in the course of a week but rather to show proof of concept: The genome does not reproduce perfectly from generation to generation, that some of these mutations are beneficial, and that these beneficial mutations can become fixed in a population through a process of selection.
Unable to argue the fundamental claim that the genome never changes because god made it perfect, that all mutations are bad, and thus evolution is impossible as a concept on a primary level, they shifted the argument to say that, "OK, so you showed that change to the genome can happen, but it's impossible to have large-scale change."
"Microevolution" and "macroevolution" are creationist terms. Now, biologists have been known to use such terms, but they usually make reference to evolutionary changes below the species level as "microevolution" and evolutionary changes above the species level as "macroevolution."
But notice, there is no distinction in the mechanisms involved when biologists refer to such things. That is, there is no "microevolutionary" process and some different "macroevolutionary" process that is distinct and different. Instead, there are simply "evolutionary processes." If the changes created by those processes don't result in speciation-level events, then a biologist might (and mind you, I said, "might") refer to it as "microevolution." But if those processes result in speciation-level events or even higher, then it might (again, mind you, I said, "might") be referred to as "macroevolution."
In essence, as far as biology is concerned, "macroevolution" is nothing more than a whole lot of "microevolution." If 1 + 1 = 2, why on earth is there anything to stop 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 10?
And, indeed, we have seen speciation happen right in front of our eyes both in the lab and in the field. The problem, of course, is the denial of the creationists to this evidence. It's essentially taking it to the next level. You see, speciation rarely results in gross morphological change. You simply don't get ostriches hatching from alligator eggs. Yet that seems to be the expectation of the creationists: They want huge morphological changes in incredibly short periods of time.
Now, evolution can happen quite rapidly. We have seen reproductive isolation happen in only 13 generations. But you aren't going to see Hyracotherium turn into Equus in our lifetimes.
But in the end, you have to remember, "microevolution" and "macroevolution" are creationist terms developed as a way to keep their claims in spite of evidence against them.
Rrhain
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