Mayan body modifications
Those of you who've seen Apocalypto may find yourselves wondering why a number of its characters sport funny-shaped heads and jewels embedded in their teeth. As it turns out, in this regard Mel Gibson is just being anthropologically correct: some Mayans really did modify their skulls' shape and have dental bling installed.
According to the digital scholars at Anthropology.net, the skulls were probably elongated by strapping boards to an infants' skull and constricting the bones from developing in a normal pattern. Unfortunately, we have no way of knowing (without doing some gruesome tests of our own) what effect this had on practitioners, neurologically or otherwise. If it's anything like the brutal practice of footbinding in China, however, which effectively crippled millions of women between 900-1900 by making their feet into four-inch hoof-like things, then it likely had a profoundly negative effect on health.