Too often, the notion of progress is used as a code word for perfection, the chain of being in a different guise. The term should be employed with caution. Some see an arrow of time in biology, as in physics, but in the opposite direction — a relentless tendency to improve, just as the universe has a built-in trend toward chaos and disorder. That is too optimistic. Some lineages get more complicated, some simpler, and much of life has to struggle to stay in the same place. If everyone is evolving, nobody can afford to stop, and there may be constant change with no overall advance at all.
