like a coral or a sea anemone does not arouse
the same feelings as looking at a creature with
two eyes—whether fish, shrimp, or octopus. An
animal that sees us can react to our actions and
interact with us. This can create an emotional
bond, which is lacking with a “blind” coral or
sea anemone.
The central part of the eye is the retina. The
retina of the human eye, which is only about
half a millimeter thick, has about seven million
color receptors and about 120 million black-
and-white receptors. They all deliver an image of
100 million points via one million fibers of the
optic nerve to the brain around 10 times per sec-
ond. The difference in brightness between twi-
light and bright sunlight, which it must be able
to cope with, reaches a ratio of one to one bil-
lion! It can differentiate up to one million color
nuances. This high-performance organ is so oxy-
gen-hungry that about half a liter of blood has to
be pumped through its vascular layer, called the
choride, every minute.
HE WHO HAS EYES CAN LOOK INTO
THE FUTURE
In many animals, none of the senses is as es-
sential to survival as seeing. For humans, it is
estimated that about 70 percent of all important
information comes from the eyes and only 30
percent from all other senses; in many animals
it seems similar. For almost all moving animals,
seeing is one of the basic prerequisites for coping
with and interacting with the environment. “He
who has eyes can look into the future,” wrote
the physicist Volker Arzt. He was referring to the
ability of animals to compare what they see with
stored memories and to calculate what is likely
to unfold next. For example, if an animal sees an
approaching predator, it can flee, hide, or con-
front an attack.
THE ROLE OF EYES IN THE CAMBRIAN
SPECIES EXPLOSION
The development of the eyes may play a central
role in the question of how the “Cambrian Ex-
plosion” occurred. This event was the sudden oc-
currence of representatives of almost all known
animal body plans and groups in a geologically
short period of five to ten million years at the
beginning of a geological period known as the
Cambrian (about 540 million years ago). To this
day, scientists are at odds over the question of
what triggered this immensely dynamic emer-
gence of new species. One explanation is the
occurrence of complex multicellular organisms,
which had more possibilities for adapting to