linguistic:paraphrasing, information:highlighting
Trade-offs

All adaptations have a downside: horse legs are great for running on grass, but they cannot scratch their backs; mammals ' hair helps temperature, but offers a niche for ectoparasites; the only flying penguins do is under water. Adaptations serving different functions may be mutually destructive. Compromise and makeshift occur widely, not perfection. Selection pressures pull in different directions, and the adaptation that results is some kind of compromise.

It is a profound truth that Nature does not know best; that genetical evolution... is a story of waste, makeshift, compromise and blunder.

Since the phenotype as a whole is the target of selection, it is impossible to improve simultaneously all aspects of the phenotype to the same degree.