[science_guy (OP)]

Why are a nocturnal animal's eyes shiny at night, and how does this help them see?

[tony6789]

it has something to do wiht some kinda color cones in their eyes

[WylieE]

Dogs and cats and other nocturnal animals with good night vision have a layer at the back of the eye called the tapetum.

  The light that comes in goes through the retina and some of it is absorbed by the rods.  What isn't absorbed passes through and hits the tapetum.  The tapetum is reflective and the light bounces off the tapetal layer and back through the retina a second time- so whatever didn't get absorbed the first time gets a second chance.  This allows them to collect the most light for seeing at night. 

This tapetum is what gives them the green / blue color in bright light.  Of course even on the second trip through the retina not all of the light will get absorbed if it is a bright light, so their eyes will reflect back to our eyes the excess light and they would look shiny. 

Colleen

[another_someone]

What is the price they pay for having a tapetum?  Does it give them greater problems in seeing in bright daylight, or does it make their eyes vulnerable in other ways?  In other words, why do other animals not have this layer?

[kdlynn]

is it true that they are color blind? does that have anything to do with that layer

[another_someone]

is it true that they are color blind? does that have anything to do with that layer

Most mammals have restricted colour vision compared to primates.

One suggestion I have seen is that there is a genetic trade off between colour sensitivity and sense of smell, so we have better colour vision as a trade for having a lessened sense of smell.

[kdlynn]

that makes sense. we can see if our food has gone bad as well as smell it, but other animals can smell it before we do but can't see discolorations

[another_someone]

that makes sense. we can see if our food has gone bad as well as smell it, but other animals can smell it before we do but can't see discolorations

Certainly, that would be part of it, but just as important is how we detect our prey when hunting, and how we communicate between outselves (we have a wide range of facial expressions and body language, but we don't go around sniffing each other as much as other animals do).

Food only really goes off if you are scavenging (it is not not clear to what extent early humans were hunters, and what extent they were scavengers).  If you are eating a fresh kill, or just recently dug something out of the soil, having the food go off is not that much of a risk, but finding the food in the first place is far more critical.

A related issue to determining whether food has gone off is determining whether food is poisonous.

At least one theory I heard was that they reason why we developed an ability to see red was to be able to detect blushing as a means of communication - not sure how seriously the theory was taken.

[kdlynn]

funny i hadn't even thought of communication. thanks george!

[tony6789]

blue flower red thorns!

[Ben6789]

Psycho. []

[tony6789]

lol