Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Most South American monkeys have color vision. But the members of one genus, Aotus , also known as "owl monkeys," do not have color vision. Scientists think that the genus evolved from monkeys that did have color vision. The ability to see color was lost when it was no longer helpful. Which other trait of the genus would contribute most to making color vision unimportant?
Large, bushy eyes.