http://www.ck12.org Chapter 1. Human Biology
FIGURE 1.83
This boy is wearing 3-D glasses; when
you look at objects and people in the
real world, your eyes automatically see in
three dimensions.Seeing in Color
For animals like us that see in color, it may be hard to imagine a world that appears to be mainly shades of gray. You
can get an idea of how many other animals see the world by looking at a black-and-white picture of colorful objects.
For example, look at the apples on the tree pictured below (Figure1.84). In the top picture, they appear in color, the
way you would normally see them. In the bottom picture they appear without color, in shades of gray (Figure1.85).
Evolution and Primate Vision
Why do you think primates, including 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