Does Environmental Change Drive Evolution?

I recently posted an article on the lack of evolution in species that have lived through several ice ages {More Evidence of Short-term Stasis]. This prompted a discussion about whether any serious evolutionary biologists really believe the opening statement in the abstract of the paper, "Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures" (Prothero et al. 2012).

I believe that lots of biologists think like this. Let's discuss a quotation from The Blind Watchmaker (1986, p.178-179) by Richard Dawkins. How many readers agree with him?

After many generations of cumulative selection in a particular place, the local animals and plants become well fitted to the conditions, for instance weather conditions, in that place. If it is cold the animals come to have thick coats of hair, or feathers. If it is dry they evolve leathery or waxy waterproof skins to conserve what little water there is. The adaptations to local conditions affect every part of the body, its shape and color, its internal organs, its behavior, and the chemistry of its cells.

If the conditions in which a lineage of animals lives remain constant; say it is dry and hot and has been so without a break for 100 generations, evolution in that lineage is likely to come to a halt, at least as far as adaptations to temperatures and humidity are concerned. The animals will become as well fitted as they can be to local conditions. This doesn't mean that they couldn't be completely redesigned to be even better. It does mean that they can't improve themselves by any small (and therefore likely) evolutionary step: none of their immediate neighbors in the local equivalents of 'biomorph space' would do any better.

Evolution will come to a standstill until something in the conditions changes: the onset of an ice age, a change in the average rainfall of the area, a shift in the prevailing wind. Such changes do happen when we are dealing with a timescale as long as the evolutionary one. As a consequence, evolution normally does not come to a halt, but constantly 'tracks' changing environment. If there is a steady downward drift in the average temperatures in the area, a drift that persists over centuries, successive generations of animals will be propelled by a steady selection 'pressure' in the direction, say, of growing longer coats of hair. If, after a few thousand years of reduced temperature the trend reverses and average temperatures creep up again, the animals will come under the influence of the new selection pressure, and will be pushed towards growing shorter coats again.

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Prothero, D.R., Syverson, V.J., Raymond, K.R., Madan, M., Molina, M., Fragomeni, A., DeSantis, S., Sutyagina, A., and Gage, G.L. (2012) Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial–Interglacial cycle. Quaternary Science Reviews 56:1–10. [doi: 10.1016/j.quascirev.2012.08.015]