Monkeys: Sight is key
Monkeys differ significantly from all the prosimians, except the tarsier in that their world is dominated not by smell but by sight. Clearly it is important for creatures of any size living in trees and, on occasion, jumping between them, to be able to see where they are going. So daylight suits them better than darkness and all monkeys, except for the South AmericanDouroucouli, (Aotus trivirgatus) are active at that time. Their eyesight is better than that of the prosimians. Not only do they see in depth, they have greatly improved colour perception. With accuracy of vision they can judge the ripeness of distant fruit and the freshness of leaves. They can detect the presence in the trees of other creatures which, in a monochrome world, might be invisible. And they can use colour in their communications between one another; monkeys because their colour-vision is so good, have themselves become the most highly coloured of all mammals.