Have you ever wondered why some people have lighter eyes than others? Differences in iris coloration have traditionally been explained as a result of sexual selection, but a recent study led by researchers from the Department of Biological Sciences at the National University of Singapore (NUS) Faculty of Science revealed that this is partly due to differences in lighting in the habitats of primate species.
source https://www.lifetechnology.com/blogs/life-technology-science-news/study-addresses-causes-of-eye-color-variation-in-primates
