Natural Selection Shrinks Herd of Kansas Darwinists, page 5

Originally posted by junglejake
we have several complete Allosaurus skeletons and, last I can recall, 3 almost complete T-Rex skeletons (info outdated by about 10 to 15 years). So we have many examples of the plateau, where the species seemed to have settled, but nothing in between.

? But we do have stuff in between. We have a few species of the genus allosaurus, and many examples of tyrannosaurs (gorgosaurs, albertosaurs, etc, are also tyrannosaurs). We have a fossils record that shows the 'big' transitions, and we're already accepting that 'small' changes are acceptable, such as having bigger jaws, loosing fingers, increasing overall size, etc.

If evolution takes place on the micro level, it would stand to reason the majority of fossils discovered would be blends of various species.

I agree, and the thing is, all fossils are transitionals. They're all moving from something on to something else (for the most part, some by chance would probably be the last species of their line)

All life today would be a blend, as well. There wouldn't be set species, there would be percentages. This is 70% rat and 30% rabbit,

I see what you are saying, and that is what we'd expect, and its actually what we find, with one reservation, that we do have species. A species has a biological reality, its simple, but its an actual thing. A species can be defined in terms of actual organisms in operating in the world, they're basically inter-breeding populations. Sometimes two populations don't interbreed (or exachange genes at a distance even), simply because they are seperated by a physical barrier, like a large gorge, or an impassible river, or simply gaps in a range, and sometimes they don't interbreed because they aren't physically able to, and sometimes because their genetics prevent it (say different chromosome numbers, etc). So we can expect there to be distinct species in the living world.

But we would expect that in terms of lineages, that we'd have great difficulty. What really seperates, say, 'tyrannosaur population A" in this upper formation and "tyrannosuar population B' in this lower, and millions of years older, formation? Obviously they're not interbreeding, but only because they are seperated by time, and, really, they are transfering genes, because they're forming a lineage with one another. So even if we give the fossils two different species names, that name sort of looses a lot of its meaning, and its basically an arbitrary distinction (whereas the seperation in species of living rabbits isn't arbitary, they're not interbreeding and exchanging genes).

So in the modern living world we see distinct species, and distinct Kinds, these are what I think we can consider Plateas (rather than species, for the above reasons). We see Birds, and Mammals, and Reptiles, and nothing that is in between.

But in the fossil record, we don't see distinct birds mammals and reptiles. We see that incredible, expected variety and mix that we expect because of the implications of evolutionary theory. We see "dino-birds" and "Mammal-like Reptiles". Over the course of the histroy that happened to play out, many linegages died out, while others surived. And the result is what we have today, where we think we are seeing these distinct kinds of animals, like birds and mammals. Its not even that intermediates are unfit or something. Its just that we've looked at the world around us and put things in to arbitrary-yet-sensible categories (because we see the living world long before the fossil world). We still have 'transitionals', like egg-laying mammals, or flightless birds and primitive birds, but we've picked the characteristics that are most obvious to us and said that they define that kind of animal (like fur, feathers, scales, egg-laying, water breating, etc etc).

So why are there these special plateaus? Why does one specie slowly, ever so slowly, evolve from one form to another before it seems to settle in, while everything in between, which was capable of survival better than the original species that still exists, dies out, without a fossil? I know fossil creation is a very unlikely process, therefore making fossil discovery very rare compared to the population as a while.

It is because of that knowledge that I find it so remarkable that we run into these set species, and several fossils of each, typically, yet nothing that seems to be a transitional form.

A transtitional species isn't going to be any different than a regular 'set' species. Its allways just a species that is adapted to its environment, a population of organisms that are being subjected to changing selective pressures. So we look at the record, and see an allosaur and a tyrannosaur and say, these are endpoints, the one underwent a transition and became the other, and then sensibly ask where is that transition. But in reality, we have the transition between two other points, say very primitive dinosaurs and very advanced tyrannosaurs. Allosaurus and Tyrannosaurus are transitions along that 'path'.

Another way to look at it is with the idea of the missing link in human evolution. We can say that man evolved from chimps (roughly). So we want to see the transitions between man and chimp, things that are mixes of both. We called this the missing link. Now, the thing is, the original population of chimps wasn't necessariyl subjected to pressure to make them into men, rather they, like all species, were simply populations of animals that were being subjected to selection pressures for their own little environment. Man is not the 'end point", or the plateau, any more than the chimp is the plateau. Because before the chimp there are other more primitive things that eventually happened to become chimps.
Anyway, the missing link was eventually found.
It was a 'stable' species, lets say it was lucy, australpithecus. It was doing what all species do, maintaining its 'species barriers', being set and stable, not mixing with other species that co-existed with it. But, at the same time, its being subjected to evolutionary pressures, and its changing, over long periods of time, into man.
If we could look at a 'video' of the whole process from chimp to man, we'd see constantly changing organisms with no distinct lines between them, sometimes more chimp like, sometime smore man like (20% chimp, 80% man, etc etc). It'd be silly to say that from frames 5 to 10 its 'australpithecus' and from frames 11-15 its 'homo habilis'. But we don't have that video, all we have is specimins from rather haphazard points along that process. And we give those points names like australpithecus and homo habilis, while recognizing that there are any numer of other populations between those two that could all be named.

So in the modern world we have rabbits, distinct from rats and chipmunks. Whereas in the fossil record, we have samplings of species from all those points, and we can't talk about 'definite rabbits' at some points. In the case of birds, we have the 'dino-birds'. You simply can't call these specimins definite dinosaurs nor definite birds, they're just points in a blended spectrum of forms. We just happen to only have one set, the birds, alive today.

So any population that is interbreeding is a species. Thats why we are able to assign fossil specimens to a species. A transitional form would, when found in the record, have characteristics of both 'plateaus' (say dinosaur teeth, snouts, hands, tails, claws, alongwith birdy feathers, backbones, skull sutures, perching feet, etc) and still, at the same time, be a stable species.

Just like a platypus. It has fur but lays eggs. Its a transitional. Its also a species. And its nicely adapted to its environment.

This 'deep time' aspect of paleontology really results in a world that is very different from the one we are used to. It has odd implications, like the one you are bringing up, with 'distinct speices' having to also undergo 'transitions', which seems completely contradictory.

Wow, that was a ramble. I hope there was some sense in there!

[edit on 3-8-2005 by Nygdan]