Emotive signaling as a possible adaptive advantage of light-coloured eyes
Blue eyes, and light-coloured eyes in general, are a comparatively unusual feature found in around 8% of the population, but are widely distributed globally and have risen in prevalence over time. The tenets of evolutionary biology posit that in order for an emergent trait to survive and become widespread it must presumably hold at least some adaptive advantage. Blue eyes have some known adaptive disadvantages such as increased sensitivity to bright light and so there has been widespread speculation about what adaptive advantages they may offer that would compensate for this drawback. Several postulates have been put forward, including enhanced facial attractiveness and less sensitivity to seasonal depression in low-light climates. Another possibility that has not yet been explored is that light-coloured eyes may have advantages for inter-personal communication; a greater colour contrast between the pupil and the iris may make changes in pupil status more apparent, possibly allowing an individual to better convey their emotional state, and may also make eye movements in general more apparent, thus enhancing communication by facial expression.