What was the primary reason proposed by Sussman for the evolution of visual adaptations in early primates?

The primary reason proposed by Sussman for the evolution of visual adaptations in early primates centers around the ability to gather fruit. This adaptation was crucial for early primates as it enhanced their ability to locate and identify ripe fruits in their environments. The development of color vision, for instance, allowed these primates to distinguish between different types of fruit and their stages of ripeness, which would have been vital for their survival and for finding nutritious food sources.

While factors like environmental changes, competition for food, and predation avoidance are significant in broader contexts of evolutionary adaptations, Sussman specifically emphasizes the role of fruit gathering as a driving force behind the visual adaptations of early primates. The adaptations were not merely incidental but rather specifically suited to improve foraging efficiency and dietary success in a frugivorous lifestyle. This focus on fruit gathering illustrates how specific ecological niches can drive evolutionary changes in sensory systems in primate evolution.