Evolution and Primate Vision
Why do you think primates, which include humans, evolved the ability to see in three
dimensions and in color? To answer that question, you need to know a little about primate
evolution. Millions of years ago, primate ancestors lived in trees. To move about in the
trees, they needed to be able to judge how far away the next branch was. Otherwise, they
might have a dangerous fall. Being able see in depth was important. It was an adaptation
that would help tree-living primates survive.
Primate ancestors also mainly ate fruit. They needed to be able to spot colored fruits among
the dense leafy background of the trees (Figure20.15). They also had to be able to judge
which fruits were ripe and which were still green. Ripe fruits are usually red, orange, yellow,
or purple. Being able to see in color was important for finding food. It was an adaptation
that would help fruit-eating primates survive.
Figure 20.15: With color vision, you can tell which cherries in this picture are ripe, because
cherries turn red as they ripen. ( 12 )
Knowing about primate evolution helps explainwhy we see the way we do. However, it
doesn’t explainhowwe see as we do. What allows us to see in three dimensions and in
color? To answer that question, you need to know how the eye works.
How the Eye Works
The function of the eye is to focus light. The parts of the eye, shown inFigure20.16, suit
it for that function. Follow the path of light through the eye as you read about it below.