According to Darwinism, biological evolution proceeds without discernible plan or purpose. To be sure, biological evolution produces things that look planned or purposed. But what underlies Darwinian evolution ultimately is a blind mechanical process--the Darwinian mechanism of natural selection.
Darwin himself argued that natural selection, though not capable of purposive action, is nonetheless capable of producing the appearance of purpose in nature. Indeed, he ascribed remarkable skill to natural selection. In The Origin of Species he wrote: "Natural selection picks out with unerring skill the best varieties." Darwin elaborated:
Natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.
In this way natural selection accomplishes all of biology's design work without being an actual designer. Natural selection is not a watchmaker per se but a blind watchmaker, to use Richard Dawkins' apt phrase. Natural selection does not operate with actual plans or purposes. It does not look into the future and deliberate about what biological structures and functions might be worth innovating. Rather, natural selection is an opportunist that takes advantage of useful variations that arise as organisms reproduce.
For this reason, even though the word "design" appears in the biological literature, one is more apt to …