Natural selection is just three factors - over-production, variation, and inheritance combined to produce adaptation to changing local environments. It's not a principle or progress; it's just a principle of local adaptation. You don't make better creatures in any cosmic sense; you make creatures that are better suited to the changing climates of their local habitats.
Stephen Jay GouldTransitional forms are generally lacking at the species level, but they are abundant between larger groups.
Stephen Jay GouldSomething deep within us drives accurate messiness into the neat channels of canonical stories.
Stephen Jay GouldBiological determinism is, in its essence, a theory of limits. It takes the current status of groups as a measure of where they should and must be ... We inhabit a world of human differences and predilections, but the extrapolation of these facts to theories of rigid limits is ideology.
Stephen Jay Gould