[Ichneumon]

You want examples of bad design? In man alone we have a spine that is not dapted for either going about on all fours, nor fully upright stance. This is one reason for the ease with which we suffer back injuries. Ditto for our knees and ankles. Humans are also the only animals that suffer constipation -- because of the near-vertical layout of our digestive tract.

My favorite example: Wisdom teeth. They made good sense back when we had a longer ape-like jaw, but since hominids evolved larger craniums and smaller jaws, we've got too damned many teeth for the available space. And no, they're not there as "spares", they most often end up impacted even when other molars have been lost. They cause a wide range of serious health problems, and provide next to no benefit.

Or maybe God put them there to make oral surgeons rich...

[Coyoteman]

Wisdon teeth: They made good sense back when we had a longer ape-like jaw, but since hominids evolved larger craniums and smaller jaws, we've got too damned many teeth for the available space.

The real problem seems to be interproximal wear, or the lack of it in a modern diet. Chewing on tough items causes very slight up and down movement of individual teeth causing wear between adjacent teeth. The teeth drift slightly toward the midline (mesial drift I think its called). This wear and mesial drift creates just enough space to allow the third molars to erupt correctly.

In some populations that eat acorns ground in stone bowls as a staple food, by the time the third molar erupts the first molar is about 1/3 worn away, but this is a pretty extreme degree of wear.