Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis

Conventionally, anthropologists have sought to explain a multitude of unique features of modern humans as the outcome of a single adaptive breakthrough. These "umbrella hypotheses" are aesthetically appealing because they appear to be parsimonious. As internally consistent hypotheses about the past, they are very difficult to prove incorrect in an absolute sense. Anthropology has often rejected them by consensus without developing explicit reasons. This essay explores one example of these models, the Aquatic Ape Hypothesis, the proponents of which continue to argue that they have not received a fair hearing among anthropologists. The hypothesis is troubled by inconsistencies and has not been reconciled with the fossil record. More importantly, its claim to parsimony is false. The numerous "explanations" for individual anatomical traits that it generates constitute premises that are not better founded than competing terrestrial "explanations". The unifying theme of aquatic adaptation is considerably less parsimonious than the assumption that our lineage has always been terrestrial. Finally, the mosaic pattern of hominid evolution demonstrated by the fossil record will not support this or any single cause theory. Most of these criticisms have been previously voiced in one form or another, yet umbrella hypotheses ranging from mainstream science to the paranormal maintain their popularity among students, general audiences, and scholars in neighboring disciplines. One reason for this is that simple answers, however wrong, are easier to communicate and are more readily accepted than the more sound but more complex solutions. Evolutionary science must wrestle with this problem both in its own community and in the education of the public.