[Dimensio]

Those same alterations would kill any who did not evolve, then. But we still have fish, and monkeys still live in trees.

The entire planet is not a single "environment". A change in the environment in one location does not translate to a change in every similar environment on the planet. Those populations in the unchanged environment would continue on as they had done before while populations in the changed environment may shift as the organisms better suited for the new environment continue on their genetic line.

[ShadowAce]

A change in the environment in one location does not translate to a change in every similar environment on the planet.

So it would be easier for a fish to walk on land than swim to a different locale?