It is difficult to extract a serious social message from such a playful novel, but there is a hint of the evils of European colonization in Africa.

Mungo Park's disappearance in the Niger River symbolizes the doom that awaits Europeans who try to conquer Africa. Park's fate is comparable to that of Mr. Kurtz in Joseph Conrad's Heart of Darkness (1902), a more serious novel on the subject of colonization. On the other hand, when Ned Rise survives the same accident on the Niger that kills Park, Boyle is sending a Darwinian/ Marxist message about the resilience of the lower classes. All of Park's formal training as a naturalist is no match for Ned's rise (pun fully intended by Boyle) from his lowly origins at the bottom of the British social ladder.