Anyone who thinks that our body is a marvel of mechanical engineering should get out a phone book and scan the listings of orthodontists, orthopedists, optometrists, and chiropractors-to name just a few specialties. Those doctors are making good livings treating our sundry flaws. Face it: our body has many features that could work much better. The sad fact is that evolution is no engineer [2657]. It's just a tinkerer [1265, 1266].

Worse than that, evolution is a myopic tinkerer. It can only solve immediate problems using available variations [226]. If its spur-of-the-moment contrivances turn out to be liabilities at a later date under different circumstances, well, that's just tough luck! Adaptations are typically quite hard to undo. In this way some of our organs have gotten themselves into predicaments akin to people in a bad marriage, who often mutter to themselves, “But it seemed like a good idea at the time!” Indeed, this familiar phrase offers a convenient shorthand for denoting the phenomenon:

A small sample of our shortcomings is sketched in Figure 6.1, and a larger batch is inventoried in Table 6.1. Other authors have discussed some of them [1103, 2384, 2824].