At one time he said that humans must have all been born with tails, which were removed by midwives at birth. His contemporaries ridiculed his views, and by 1773 he had retracted this opinion (Pringle 1773). Some later commentators have seen him as anticipating evolutionary theory. He appeared to argue that animal species adapted and changed to survive, and his observations on the progression of primates to man amounted to some kind of concept of evolution. Burnett also examined feral children and was the only thinker of his day to accept them as human rather than monsters. He viewed in these children the ability to achieve reason. He identified the orangutan as human, as his sources indicated it was capable of experiencing shame.