Kachi wrote:
And to some extent, that's how we test macro-evolution-- we don't have recorded data, but we do have evidence in the form of fossils and genetic data.
Of course. We're on the same page here. The problem is that very very few fossil records have been found that support the theory itself. Certainly, far far fewer than what would be predicted. We should be finding tons of fossils showing intermediate stages between various otherwise similar species, but we don't. That's a tremendous problem. How you "test" macro-evolution is you predict that a species with properties X,Y, and Z should have existed between Species A and Species B. Then you look for what you predicted.
We haven't found nearly enough. Not even remotely enough if this has been going on constantly over the time periods in question for every single species that exists now and has ever existed. What we do find occasionally are completely new species, but not with the predicted properties, which makes the puzzle worse since there's now more extinct species we keep finding for which we *also* can't trace sufficient paths back to common ancestors.
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Two things. First of all, we know that micro evolution happens, and that macro evolution is at least possible.
No one's doubting micro-evolution (at least not me). And no one's saying that macro-evolution isn't possible. We just don't have sufficient evidence showing it happened. It's like waking up in a field in your car. You can assume you drove your car to get there, but you don't know for sure. Then you walk back and you find that the road is washed out and has been for months. And there are no tire tracks. And the engine doesn't work. And the tires are missing. And a row of undamaged bushes completely covers the only routes you could have driven. And the more you look, no matter how much you assume that you must have driven your car to get here, you keep seeing a complete lack of any indication that you *could* have driven here. You assume you must have because you're in a car, but that's all you have.
That's kinda where macro-evolution is right now. And at some point, you perhaps start to think that maybe you were abducted by aliens and then beamed down to the field or something, because as much as there's no evidence at all for that, it at least explains what you are seeing.
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It does stand to reason that millenia of micro evolutions will cover a substantial portion of macro evolutions, but we rely on fossil records for most of this data, and the problem with fossil records is that we only get very brief snapshots of the flora and fauna of that time. To use a loose analogy, it'd be like trying to guess how you got to be a middle-aged man based only on a recent picture and a baby picture. We know it happened, but without pictures of every developmental step, we have to wonder, "How can this be the same person? How can we know that it is?"
Yup. Still a problem though. Our "snapshots" aren't just start/finish for each species. They are time based. If you took a snapshot only once every 50 years and looked at just the photos of one person, you'd have a huge gap. But not every person is born at the exact same time, in the same way that every member of an evolving species will presumably not be at the same stage at the same exact time. If you looked at all the pictures of all the people taken during each of those picture taking events 50 years apart, you'd have all the evidence of "people" at all stages of age between birth and old age.
We don't see the equivalent in the fossil record. And that's a problem.
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The other thing is that we have to remember that evolution happens as a result of random mutations, and that those random mutations survive through fitness (but sometimes they don't-- it's just a probability). There is potential for a new species to be created rapidly through crossbreeding and/or mutation. We can never hope to show this in a fossil record because it's not a gradual change.
That's valid. So if we restrict ourselves only to random mutations, it explains the lack of fossil record. Um... But there are other issues with the random mutation angle as well (as you presumably know).
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We can only observe it when it happens. Crossbreeding in particular becomes less plausible with time-- most modern species are too differentiated to crossbreed now, but may not have been in an era of less biodiversity.
Yeah. Here's the problem though. We can't really find eras with "less biodiversity". Obviously conditions affect which sorts of species are dominant over time, but within those time frames there's still a hell of a lot of diversity. So we're left with the problem that in order to "miss" the formation of that much diversity, it must happen really really fast. But if it happened that fast, we'd see far more evidence of it happening all around us all the time. But all we can see is relatively minor changes to existing species (adaptations mostly). Nothing that would make something no longer be identifiably a member of the same species.
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There's the other possibility that (basically) a mother gives birth to a genetically mutated litter who breed and propagate a significantly different offspring. Of course, mutations like these happen all the time-- usually they're bad mutations that don't improve survivability. But occasionally they promote survivability, or at least don't hurt it. Generally this is microevolution, but theoretically it could cause macroevolution-- it would just be such a rare event that there's no way we could hope to see it within our lifetime, a lifetime in which evolutionary science has only just begun.
Sure. Absolutely possible. But still basically just a guess, right?
Edited, Nov 30th 2010 2:30pm by gbaji