Originally posted by Moldy Crow
This , sir is incorrect . The fossil record combined with The Theory of Punctuated Equalibrium gives a very complete picture of the evolution of higher species .

Punctuate Equilibrium is precisely what I was referring to when I said there were explanations for the scant fossil record. It is a great acheivement of theoretical biology, but the scant record remains. Why is this not nearly as supportive as a wealth of actual transitional fossils? Because that would be empiricle evidence.

Originally posted by Coletti
If nothing drives it, then it must be random. And if it's random, then it does not evolve.

You are very confused . Natural selection does not evolve , a population of a species evolves . You asked what causes species to evolve , I told you the answer .

Natural Selection is a causitive set of circumstances which "drives" evolution . One of those factors is chance or as you call it , randomness . Other factors could be a mix or combination of many of the following : climate , predation , disease , meteors , availibility of food , mating selection preferences , etc .

This is the simplified mechanism , and I hope answers/addresses where you seem to be going :

An organism produces more offspring than can survive . Those offspring have a variety of traits , in that I mean they are not identical . Some have big feet , some small . Some have greater genetic resistance to parasites , some not quite so much so . Some big antlers , some small ...etc. Those offspring most suited to the environmental conditions(or natural sellection factors) will have a greater chance of surviving and passing these traits on to offspring . Those not suited to the environmental conditions will have a greater chance of dieing and therefore do not pass on their traits to offspring . Natural Selection discribes the combination of these factors and the process of winnowing away the members of the population less suited to the environment . "It" , does not act with consciousness or forethought . "It" does not have a plan or agenda . "It" does not evolve . "It" is a combination of constantly changing conditions that does include at times , a random roll of the bones .

And no Kelly , it's not an "after the fact occurance" . It's a constant . Sometimes quite obvious and dramatic like a dought , sometimes very subtile like birds choosing mates with only certain color patterns . And it drives evolution .

Originally posted by Coletti
What is the mechanism that pushes a succession of microevolutionbary changes adding up to macroevolution?

"Pushes"?

Evolution is a process by which organisms change in an inheritable manner. It takes place at a certain rate of genetic change over time. More time means more genetic change which allows more exaggerated phenotypic differences.

Natural selection is the process that weeds out most of the tremendous number of possibilities and leaves only those organisms that can most effectively survive and thrive.

The difference between microevolution and macroevolution is just a difference of degree.

I guess the mechanism in short is time as well as natural selection.

Originally posted by Coletti
If nothing drives it, then it must be random. And if it's random, then it does not evolve.

If nothing drives it, then it must be random.

I don't think I agree with this. I guess it depends on what you mean by "drives". What drives gravity? You'll probably say God. Well, what drives God?

Natural selection is non random in that organisms that survive better in their environment pass on their genes more effectively to future generations.

Originally posted by KellyJay
Natural selection is an after fact occurance, it does not drive anything.
Kelly

Macroevolution would happen without natural selection in that organisms would get more and more different from extreme to extreme than they were at earlier times in the evolutionary process. Natural selection is why we only see certain kinds of organisms rather than every conceivable type.