Pinheads were extremely popular freaks with showmen, because of their unusual and primitive appearance. They usually suffered from microencephaly or other forms of mental retardation. They were usually promoted as Darwin's missing link, and were billed under names such as The Wild Men of Borneo or The Ancient Aztec Children.
 
The first Pinhead was Zip the What is It? P. T. Barnum found and enlisted William Henry Johnson in 1860, billing him as the missing link. With this new act, he was able to ride the popularity of Darwin's Origin of Species which had been published three months earlier. In later years he simply went by the name Zip, and his performances consisted of standing in a small cage, dressed in a fur suit.
 
Another popular attraction were two pinhead children billed as the Ancient Aztec Children. Barnum claimed they had been found in an Aztec temple, while being worshiped as gods by the local people. Their act consisted of dancing around in Tunics and speak gibberish, billed as their native tongue.