The barfly is involved in a fierce evolutionary arms race against the lounge lizard, much like cheetahs are against gazelles (or perhaps I should have put that the other way around). I just thought I'd pass on this well-known fact for those few who were unaware. Jerry Coyne has never revealed the point on his blog, so the responsibility has fallen on me.
If I were more artistic, I'd create an illustration to make the point more powerfully. A picture is worth a thousand words, after all. If anyone provides a suitable one with no copyright issues, I'll reward him or her by displaying it here. (Think of this as a competition if you like.)