The Great Hippocampus Question was a 19th-century scientific controversy about the anatomy of ape and human uniqueness. The dispute between Thomas Henry Huxley and Richard Owen became central to the scientific debate on human evolution that followed Charles Darwin's publication of On the Origin of Species. The name comes from the title of a satire the Reverend Charles Kingsley wrote about the arguments, which in modified form appeared as "the great hippopotamus test" in Kingsley's 1863 book for children, The Water-Babies, A Fairy Tale for a Land Baby. Together with other humorous skits on the topic, this helped to spread and popularise Darwin's ideas on evolution.