I think the key point here is that selection for form need not be intentional. Taller plants are able to collect more sunlight, and collecting more sunlight mea

I think the key point here is that selection for form need not be intentional. Taller plants are able to collect more sunlight, and collecting more sunlight means they are more likely to have many descendants. This does not happen because someone had the intention for the plants to be taller, but because of the physical fact that sunlight will hit the leaves of tall plants before it has a chance to reach the leaves of short ones growing below. Natural selection only cares about form insofar as it affects reproduction, but since form absolutely does affect reproduction, the result is that natural selection acts on form.