1
00:00:00,633 --> 00:00:02,767
[music playing]

2
00:00:09,600 --> 00:00:12,367
NARRATOR: While most
humans are sound asleep,

3
00:00:12,367 --> 00:00:16,800
many animals have
their eyes wide open.

4
00:00:16,800 --> 00:00:18,567
And why such late nights?

5
00:00:18,567 --> 00:00:20,900
Because some of these
animals can see in the dark

6
00:00:20,900 --> 00:00:22,667
far better than we can.

7
00:00:22,667 --> 00:00:26,467
So which animals can navigate
by night, and how do they do it?

8
00:00:26,467 --> 00:00:29,166
For animals like the
tarsier and slow loris,

9
00:00:29,166 --> 00:00:31,266
it's their large eyes.

10
00:00:31,266 --> 00:00:33,700
Larger eyes with
larger pupils allow

11
00:00:33,700 --> 00:00:35,500
more light to be taken in.

12
00:00:35,500 --> 00:00:37,533
The more light
taken in by an eye,

13
00:00:37,533 --> 00:00:40,433
the better an animal can see.

14
00:00:40,433 --> 00:00:43,033
And while the tarsier's
eyes provide greater vision,

15
00:00:43,033 --> 00:00:45,734
they also have some
minor drawbacks.

16
00:00:45,734 --> 00:00:47,834
Since their eyes are
fixed in their sockets,

17
00:00:47,834 --> 00:00:49,934
they must rotate their
heads to look from side

18
00:00:49,934 --> 00:00:54,066
to side, up to 180 degrees.

19
00:00:54,066 --> 00:00:56,867
And yet, the tarsier's
head-turning vision is only one

20
00:00:56,867 --> 00:01:00,233
of a number of animals
with such gifted sight.

21
00:01:00,233 --> 00:01:03,633
The owl, also with fixed eyes
and excellent night vision,

22
00:01:03,633 --> 00:01:06,834
can twist its neck
up to 270 degrees

23
00:01:06,834 --> 00:01:09,800
so it can see in
nearly every direction.

24
00:01:09,800 --> 00:01:12,867
With 10 times the night
vision capabilities as humans,

25
00:01:12,867 --> 00:01:15,100
they're experts at
maneuvering through trees

26
00:01:15,100 --> 00:01:17,500
in search of a midnight meal.

27
00:01:17,500 --> 00:01:19,900
But birds are far
from the only animals

28
00:01:19,900 --> 00:01:22,567
to have evolved eyes
for seeing in the dark.

29
00:01:22,567 --> 00:01:25,233
Many cephalopods,
such as the octopus,

30
00:01:25,233 --> 00:01:27,900
have proportionally large
eyes that help them search

31
00:01:27,900 --> 00:01:30,533
for food when light is lacking.

32
00:01:30,533 --> 00:01:33,834
In fact, it's not only the size,
bought also the shape which

33
00:01:33,834 --> 00:01:35,834
makes a difference in the dark.

34
00:01:35,834 --> 00:01:38,934
Though technically colorblind,
the w-shaped pupils

35
00:01:38,934 --> 00:01:41,300
of the cuttlefish allow
light into the eye

36
00:01:41,300 --> 00:01:44,166
from many directions,
spreading out the wavelengths

37
00:01:44,166 --> 00:01:47,834
and possibly allowing
them to determine color.

38
00:01:47,834 --> 00:01:50,967
Different species even
evolved similar pupils.

39
00:01:50,967 --> 00:01:53,934
For example, hunters such
as crocodiles and cats

40
00:01:53,934 --> 00:01:57,800
both have slit pupils that are
vertical instead of horizontal.

41
00:01:57,800 --> 00:02:00,533
Vertically elongated
pupils are much more common

42
00:02:00,533 --> 00:02:02,533
in ambush predators
and provide better

43
00:02:02,533 --> 00:02:04,734
depth perception of prey.

44
00:02:04,734 --> 00:02:07,467
These animals also share
a thin reflective layer

45
00:02:07,467 --> 00:02:10,600
behind the retina called
a tapetum lucidum.

46
00:02:10,600 --> 00:02:14,734
It's this layer that causes eyes
to appear to glow in the dark.

47
00:02:14,734 --> 00:02:18,033
Found in many species, this
layer acts like a mirror.

48
00:02:18,033 --> 00:02:19,967
It reflects light
back into the eye

49
00:02:19,967 --> 00:02:22,133
providing more light
to see and therefore,

50
00:02:22,133 --> 00:02:24,934
better eyesight in dim light.

51
00:02:24,934 --> 00:02:28,400
Vision is a complicated process
and one humans are still

52
00:02:28,400 --> 00:02:31,400
researching, not only to
discover just how differently

53
00:02:31,400 --> 00:02:34,633
other animals see the world
but to inspire high-tech camera

54
00:02:34,633 --> 00:02:37,066
design, medical
imaging, and perhaps,

55
00:02:37,066 --> 00:02:40,400
one day, even synthetic
retinal implants.

56
00:02:40,400 --> 00:02:43,166
At least for now, while animals
like the owl and tarsier

57
00:02:43,166 --> 00:02:46,166
are alert at night, we can
rest our eyes so they work

58
00:02:46,166 --> 00:02:48,233
best when the sun comes up.

59
00:02:48,233 --> 00:02:50,300
[music playing]