Why did anatomists once list 180 "useless" parts of the human body?

Because they were cataloguing the leftovers of evolution. In 1893, the German anatomist Robert Wiedersheim published a list of 86 human organs he judged to have become "wholly or in part functionless," organs that may be "rightly termed Vestigial." Later versions of his list grew to as many as 180, and at the famous Scopes trial a zoologist used that number to call a human being "a veritable walking museum of antiquities." What they were describing is vestigiality: the retention of structures that have lost some or all of the function they had in an ancestor.

The idea goes back further than Wiedersheim. Aristotle noted in the 4th century BC that moles have shrunken, "stunted" eyes, and Darwin later listed the ear muscles, wisdom teeth, the appendix, the tailbone, body hair and a fold in the corner of the eye as human examples. Across the animal kingdom the examples pile up: ostriches and emus still grow wings they cannot fly with, and boas and pythons keep two tiny pelvic spurs, remnants of a pelvis.

Vestigial does not always mean useless, though. The human coccyx is a shrunken tail, but it now anchors muscles that support the pelvic floor. Goosebumps still fire up under stress, a reflex left over from a time when raising body hair made an ancestor look bigger to a predator. And buried in human DNA is a broken gene that, in most other mammals, still makes vitamin C. A trait that loses its value usually isn't deleted: if carrying it costs nothing, natural selection may never phase it out.