The hypothesis was initially proposed by the marine biologist Alister Hardy in 1960, who argued that a branch of apes was forced by competition over terrestrial habitats to hunt for food such as shellfish on the sea shore and sea bed, leading to adaptations that explained distinctive characteristics of modern humans such as functional hairlessness and bipedalism. Elaine Morgan's 1990 book on the hypothesis, "Scars of Evolution", received some favorable reviews but was subject to criticism from the anthropologist John Langdon in 1997, who characterized it as an "umbrella hypothesis" with inconsistencies that were unresolved and a claim to parsimony that was false.