Adaptive myopia: how nearsightedness on land helps us underwater
Myopia, or nearsightedness, is a common condition in humans, making it an interesting trait to study from an evolutionary perspective. Although the morphology of the human eye evolved under conditions whereby light entered predominantly through air, we propose that the high prevalence of myopia might be partially attributed to an ancestral past tied to a reliance on seeing in aquatic conditions. Specifically, myopia likely provided an advantage to humans living in environments conducive to foraging and fishing underwater. Four lines of evidence support this hypothesis. First, semi-aquatic mammals are myopic when looking through air (see). Second, humans with myopia see better underwater compared to those with ordinary vision (see). Third, human populations evolving in close association to aquatic environments with clear water (Southeast Asia) have a higher prevalence of myopia than those that evolved without such an association [(see)] (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3740568/). Fourth, the Moken people of Austronesia evolved a cultural adaptation to enhance underwater vision far better than Europeans by learning how to constrict their pupils to produce a myopic condition [(see)] (http://www.ncbi.nlm.nih.gov/pubmed/12747831). While myopia is largely considered detrimental and a byproduct of developing within modern environments, these points suggest that the prevalence of this condition may also be attributed to an underlying adaptive value.