Random Mutation Vs. Natural Selection

[Lestat]

I'd like to bring myself at least up to a basic understanding of evolution. I wonder if I can do that through this forum. So please forgive the sophomoric questions.

Suppose you had a single species that got geographically separated by a cataclysmic earthquake. Maybe it produced high mountain ranges or something.

In scenario one, assume the climate, resources, and predators remain the same for each group. After many many generations how would we expect these two groups to differ, if at all? Would random mutation alone necessitate two distinct species over time? If there were no random mutation, can we expect natural selection to follow the same course (i.e. if the *same* new predators and prey came on the scene at the same time, would they evolve pretty much the same?).

In scenario 2, suppose there is a significant climatic change between the two groups. Now how much of a difference can we expect after many many generations? I would imagine quite a bit. In fact, if random mutation were involved could the new species appear entirely unrelated?

Also, wouldn't such a scenario create a gap in the fossil record? I mean that you wouldn't expect to see a slow gradual evolutionary process if the separation were sudden.

Feel free educate me in any other area of evolution as well. Just talk babyy talk. Thanks.

[bunny]

Some thoughts from an equally uneducated source (ie me):
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I'd like to bring myself at least up to a basic understanding of evolution. I wonder if I can do that through this forum. So please forgive the sophomoric questions.

Suppose you had a single species that got geographically separated by a cataclysmic earthquake. Maybe it produced high mountain ranges or something.

In scenario one, assume the climate, resources, and predators remain the same for each group. After many many generations how would we expect these two groups to differ, if at all? Would random mutation alone necessitate two distinct species over time? If there were no random mutation, can we expect natural selection to follow the same course (i.e. if the *same* new predators and prey came on the scene at the same time, would they evolve pretty much the same?).

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The two groups would evolve, given enough time, into two separate groups who could inhabit the same environment.

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In scenario 2, suppose there is a significant climatic change between the two groups. Now how much of a difference can we expect after many many generations? I would imagine quite a bit. In fact, if random mutation were involved could the new species appear entirely unrelated?

Also, wouldn't such a scenario create a gap in the fossil record? I mean that you wouldn't expect to see a slow gradual evolutionary process if the separation were sudden.

Feel free educate me in any other area of evolution as well. Just talk babyy talk. Thanks.

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I'm pretty sure the speed of evolution isnt determined by the speed of the environmental change. I think if it is very sudden and the species in question has a slow evolutionary rate (which is a hard thing to determine, but is known to vary) then it is just more likely to go extinct than a species which evolves more rapidly.

In other words, sudden change implies mass extinctions, not lots of new species (although I guess mass extinctions may make it easier for new species to survive). A much simpler explanation for a gap in the fossil record is just how unlikely it is for fossils to form.

[madnak]

Scenario one is hard to answer. You're assuming that everything is the same between the two species, but ecosystems are dynamic. Assuming two parallel universes in which everything is the same...

It's possible that both populations would just stay the way they are. It's possible they'd evolve in the same way. It's possible they'd diverge. For this scenario there are no pat answers. Not yet, at any rate.

For scenario two... Well, the specific mechanics of macroevolution are still in dispute to some degree. I think most scientists would agree that speciation would occur relatively rapidly, and definitely the change in environment and the isolation of the populations would result in divergence.

I don't know about the fossil record, or much care frankly. The idea of a "complete" fossil record is something of a myth. A "complete" fossil record would basically entail a full genealogical history back to the earliest organism. A relatively small proportion of organisms will be preserved in the fossil record, therefore "gaps" in the record will be the rule.

The value of the fossil record doesn't lie in documenting every adaptation that has ever occured, much less every trait that any organism has ever exhibited. The fossil record provides evidence for evolution primarily in that it corroborates all the other evidence.

The fossil record is consistent with the predictions of Darwin, Mayr, and other evolutionary theorists. Fossil systematics are consistent with molecular systematics - in other words, the "branches" of evolution that fossils indicate are the same as the "branches" that genetic information indicates. The fossil record is geologically very interesting - the things we can determine based on geology about climate conditions and geography (for example) "fit" very closely with the theory of evolution. The way speciation "fits" with the model of continental drift is a good example of this - ancient fossils from regions that were once geographically continuous but are now isolated are very similar, whereas modern species in the regions may be very different. And of course, finds of australopithecus and [censored] habilus and dinosaurs are, at minimum, very interesting. Does the fact that giant reptiles and "human-like" beings existed on Earth necessarily imply evolution? No. But it does raise some interesting questions that only evolution has been able to answer.

The important thing is that the idea of a "missing link" is just bunk. One of the reasons religious people complain about "gaps" in the fossil record is because it's very convenient for them. If we fill a gap between A and E with C, that just creates two new gaps - between A and C and between C and E. Now instead of one "missing link" at C we have two "missing links" at B and D!

[Borodog]

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I'd like to bring myself at least up to a basic understanding of evolution. I wonder if I can do that through this forum. So please forgive the sophomoric questions.

Suppose you had a single species that got geographically separated by a cataclysmic earthquake. Maybe it produced high mountain ranges or something.

In scenario one, assume the climate, resources, and predators remain the same for each group. After many many generations how would we expect these two groups to differ, if at all?

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Even selectively neutral variation can change frequency within a population over time, simply by random chance. Think about this: Assume that you have a population of 1000 people with 1000 different last names. Asumme that each generation, all the males and females pair up (randomly), get married, and have two children (one boy and one girl, to make our example simpler), who are given their father's last name. After a sufficient amount of time has passed, there will be only one last name shared by everyone. This is true even though that name is in no way better than any of the other 999 last names (or more specifically in this case the other 499 original male last names, since all the original female last names are immediately lost after the first generation).

The same thing works with different "flavors" of genes in the population (alleles); the frequencies of differing genes can drift randomly if they are selectively neutral.

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Would random mutation alone necessitate two distinct species over time?

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Yes. There exist modern species, like the coelocanth, that appear to be indistinguishable from fossils that are severl hundred million years old. But because of the accumulation in changes in their DNA, there is no possible way they could interbreed if you could bring the ancestral species forward in time to the present day. All kinds of changes can take place in the genome that is selectively neutral but would prevent interbreeding. The number of chromosomes can changes, genes can be copied multiple times, they can switch places in the genome, even to entirely different chromosomes, etc., none of which necessarily produce selective difference.

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If there were no random mutation, can we expect natural selection to follow the same course (i.e. if the *same* new predators and prey came on the scene at the same time, would they evolve pretty much the same?).

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Again, as the last name example shows, the two populations could drift apart even in the complete absence of differing selective pressures and new variation. Imagine a bell curve distribution of variation in some trait, like neck length, in the original population. Assume that the shortest possible neck length allowable by the available variation is no "better" (in the Darwinian sense) than the longest possible neck length. It is then entirely conceivable that in the two separated populations, the one could become fixed at the short neck length, and the latter fixed at the long neck length, and all the variation in between randomly lost.

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In scenario 2, suppose there is a significant climatic change between the two groups. Now how much of a difference can we expect after many many generations?

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An incredible amount. As I mentioned earlier, within 5 million years after the dinosaurs become extinct, small shrewlike mammals had radiated into an amazing variety of sizes and shapes, including things the size of rhinos.

Dawkins recounts an amazing story of how Russian researchers set out to domesticate the wild silver fox. In only twenty years they had bred an animal that wes for all intents and purposes a dog (not that it could interbreed with a dog, which it almost certainly would not and could not; well maybe it could produce sterile hybrids; I'm not sure if foxes can hybridize with dogs), not just any dog, but a dog that looked and behaved exactly like a border collie, with a black and white fluffy coat, "cute" floppy ears, and that craved human companionship. That's in 20 years. In other words, the variation was already there, hidden in the gene pool, no mutations required.

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I would imagine quite a bit. In fact, if random mutation were involved could the new species appear entirely unrelated?

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All species are clearly related when you look at them at a molecular level. You can easily tell, for example, that all animals are more closely related to all fungi, and vice versa, than they are to any plant. The genetic code itself, with a handful of small exceptions, is identical in every living organism on Earth. In other words, the evolution that crafted the code itself occured entirely before the last common ancestor of all modern life existed.

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Also, wouldn't such a scenario create a gap in the fossil record? I mean that you wouldn't expect to see a slow gradual evolutionary process if the separation were sudden.

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The fossil record is expected to be filled with gaps. In fact, you can easily predict it to be almost entirely gap. It would be far less of a problem to explain if there were no fossils at all than if there were far more fossils than there are. An extremely generous estimate is that one in a million individuals that has ever lived has fossilized, and that's probably generous by orders of magnitude. Also, speciation events tend to occur in small populations (for purely mathematical reasons; larger populations have more "inertia" to their genome), and at the edges of a species' geographical range, i.e. in a much smaller geographical area than the bulk of the species exists in.

So what do you expect to see? A) Almost no fossils. B) Most fossils you find will probably come from large populations, until c) a new species evolves in an isolated space and then rapidly (in terms of the geological record) "invade" and replace the previous species. So you get a record that is filled with gaps and tends to show (somewhat) long periods of "equilibrium" puncuated by periods of change where old species are replaced by new ones.

Having said that, there are indeed plenty of example of 10 million year long lineages that show gradual evolution (mollusks, horses, etc).

In other words the theory predicts exactly what we see in the fossil record.

[Rduke55]

Jeez, I leave the internet for a couple of days and there's a bunch of interesting evolution threads.

While selection and drift are not isolated, for each of the scenarios the size of the populations matter a great deal. In smaller populations genetic drift (the random part) plays a bigger role - while in larger populations gene flow (exchange of different genes) stabilizes the pool and genetic drift plays a much smaller role.

[Borodog]

^ What he said. ^

[Jasper109]

Borodog - excellent post

[soon2bepro]

Random mutation and natural selection can't exist without each other