Evolution is an incremental process. It can’t make huge jumps, Only small changes, each of which must be immediately beneficial. Major changes are difficult to accomplish even for human engineers. Fires occurred when a popular line of pickup truck was struck from the side because the gasoline tanks were located outside the frame. But to locate the tanks within the frame would require a major redesign of
everything now there, which could cause new problems and require new compromises. Even human engineers can be constrained by his- torical legacies. Similarly, our food passes through a tube in front of the windpipe, and must cross it to get to the stomach, thus exposing us to the danger of choking. It would be more sensible to relocate the nostrils to somewhere on the neck, but that will never happen,