Hi, Europa.
I would like to input a little into this discussion: I hope you don't mind the intrusion.
Europa writes:
Do you guys honestly believe that the environment can remain similar for an organism for 200 million years?
Yes, they do. And, so, by the way, do I.
Perhaps we shouldn’t say, the environment can remain similar; it would be more accurate to say, the
selection pressures caused by the environment can remain similar, even while the environment changes.
This is because change is inevitable: we all think that all lineages and all environments will inevitably change over time. But, sometimes change means switching like for like.
For instance, an oak forest provides places for squirrels to live in and nuts for squirrels to eat. And, a pine forest also provides places for squirrels to live in and nuts for squirrels to eat. So, squirrels can probably make the evolutionary transition from oak habitats to pine habitats without altering their overall morphology all that much. So, there is no real pressure for squirrels to inherit major modifications to their body plan.
Dinosaurs came to watering holes in the Cretaceous in much the same way mammals come to watering holes today, and the adaptations of crocodilians for killing a drinking dinosaur work just as well on a drinking mammal. So, crocodilians can probably make the evolutionary transition from dinosaur-inhabited ecosystems to mammal-inhabited ecosystems without altering their overall morphology all that much. So, there is no real pressure for crocodilians to inherit major modifications to their body plan.
But, sometimes change means switching like for unlike.
Grass is an entirely different kind of plant from cycads and ferns. The mouthparts that were suitable for plucking and chewing cycads were not suitable for plucking and chewing grass. So, when grasses first began appearing, modifications to the mouthparts were required as part of the evolutionary transition to this new environment. These animals experience pressures that favor change.
Animals are less buoyant in air than in water. So, land-living animals have to support much more of their own weight than do water-living animals. So, modifications to the limbs and skeletons were required as part of the evolutionary transition between water and air environments. These animals experience pressures that favor change.
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Not all evolutionary situations are equivalent to one another, so it shouldn’t be a surprise that not all evolutionary situations result in the equivalent outcomes. It also shouldn’t be a surprise that not all evolutionary situations result in the same rate or the same extent of change.
Edited by Bluejay, : "...live in..."
-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.
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