- [Narrator] For some animals, it's not about the hunt.
It's about foraging for food.
So how does vision help with that?
Gorillas see things exactly the way humans do.
They see the yellow mango...
and the green celery.
The red ball clearly caught this little gorilla's attention.
Turns out gorillas and other great apes,
like orangutans and chimpanzees,
have a much wider range of color vision than most mammals.
Color vision is a relatively recent development primates
and a big evolutionary advantage.
The earliest primates were tiny, nocturnal creatures
that stayed close to the ground and only came out night.
That way they could have dinner and not be dinner.
As night-crawlers, they relied more
on seeing shapes and movement than color.
At this point, they use their sense of smell
more than their eyesight.
Eventually primates moved up into the trees,
but they still had limited color vision.
These lemurs are direct descendants
of the early tree-living primates.
Like other nocturnal animals,
they have a lot of rod cells in their eyes,
which help them see well in the dark,
but fewer cones for color detection.
They see in shades of green and blue,
because they have just two types of color photoreceptors.
This is called dichromatic vision.
The same goes for many of the monkeys
of Central and South America,
like these squirrel monkeys.
But at some point in their evolution,
old world monkeys from Africa and Asia,
like baboons and macaques, evolved trichromatic vision.
They have three types of color receptor cones,
not just sensitive to blue and green, but red as well.
This type of vision requires medium to bright light.
But as old world monkeys became diurnal
and foraged in the day, it worked to their advantage.
Scientists believe primates evolved trichromatic vision
because it helped pick out good fruit to eat,
which helped them survive.
One way to tell the ripeness of fruit
is by touching it to see how soft it is.
But it's usually easier to tell by looking at it.
Red fruits are usually sweeter and easier to digest.
For baboons, red also signals readiness for sex.
As primates moved into trees
and away from the source of smells on the ground,
sight became more important than smell.
After all, primates can see further than they can smell.
With less ability to pick up smells
and pheromones in the air,
primates needed more visual cues for sex.
Even when the great apes emerged
and evolved to spend more time on the ground,
the advantages of full color vision continued.
(upbeat music)
With the most complex vision in the world
and a punch thrown faster than a speeding bullet,
this technicolor creature is an underwater superhero.
The mantis shrimp is neither mantis nor shrimp,
but it delivers the ultimate knockout.
It's strike really is faster than a speeding bullet.
A .22 caliber to be exact.
It's the fastest move in the ocean,
which means it needs excellent eyesight
to keep its eyes on the prize.
Fortunately, evolution took care of that.
Mounted on mobile stalks that move independently,
the mantis shrimps compound eyes
are unlike any other on Earth.
Each eye is divided into three parts,
giving the mantis shrimp trinocular vision.
This enables depth perception using just one eye.
It's a big advantage for a hunter.
The constantly moving eye stalks allow the mantis shrimp
to scan a huge area of its environment.
Each eye part is specialized and serves a specific purpose.
The upper and lower parts mainly recognize form and motion.
The middle has six rows of ommatidia that detect color.
Where humans have three color photoreceptors,
mantis shrimp have at least 12.
But despite having four times as many receptors,
experiments have shown that they can't see
as many colors as humans can.
Their eyes are more tailored for speed and efficiency.
The mantis shrimp rarely leaves home except to eat.
It just needs to know if something is prey or predator.
This unique visual system
allows them to figure that out quickly
without wasting time and energy on brain processing.
Unlike humans, it skips sending visual stimuli to the brain
and does its processing in the eyes themselves.
It also has a territorial temperament
driving it to kill anything that comes too close.
This is one of the most aggressive hunters
in the animal kingdom.
With those highly developed eyes, it's easy to see why.
(upbeat music)