Why does a mammalian (human) eye focus?
How does it know that object in front of it needs to be focused on?

http://sciencelearn.org.nz/Contexts/Light-and-Sight/Science-Ideas-and-Concepts/How-the-eye-focuses-light

Yes but why?

Evolution. You don’t focus, you don’t see, you don’t eat, you don’t survive.

buffy said:

Evolution. You don’t focus, you don’t see, you don’t eat, you don’t survive.

and/or you don’t focus, you don’t recognise food or poison.

There are plenty of examples of animals which don’t use sight and they do fine but I’m not talking about evolution.

I’m specifically referring to the function which causes an eye to focus. Anyone know how it does?

It would be feedback from the visual cortex adjusting the focal length of the lenses (by squeezing or stretching) to reach optimal focus. Part of the huge range of tasks that the CNS attends to without us having to consciously issue instructions. As buffy says, this automatic operation is a product of evolution by natural selection.

Bubblecar said:

It would be feedback from the visual cortex adjusting the focal length of the lenses (by squeezing or stretching) to reach optimal focus. Part of the huge range of tasks that the CNS attends to without us having to consciously issue instructions. As buffy says, this automatic operation is a product of evolution by natural selection.

There is little point comparing sighted animals with unsighted ones in the above context, as each would live in a different habitat, where either sight was an advantage for survival, or with blind animals not required, as there was no advantage in having sight.

PermeateFree said:

Bubblecar said:

It would be feedback from the visual cortex adjusting the focal length of the lenses (by squeezing or stretching) to reach optimal focus. Part of the huge range of tasks that the CNS attends to without us having to consciously issue instructions. As buffy says, this automatic operation is a product of evolution by natural selection.

There is little point comparing sighted animals with unsighted ones in the above context, as each would live in a different habitat, where either sight was an advantage for survival, or with blind animals not required, as there was no advantage in having sight.

I watched a documentary on Darwin last night and they covered the evolution of eyes including the below animal with its impressive ability
https://en.wikipedia.org/wiki/Mantis_shrimp

Cymek said:

PermeateFree said:

Bubblecar said:

It would be feedback from the visual cortex adjusting the focal length of the lenses (by squeezing or stretching) to reach optimal focus. Part of the huge range of tasks that the CNS attends to without us having to consciously issue instructions. As buffy says, this automatic operation is a product of evolution by natural selection.

There is little point comparing sighted animals with unsighted ones in the above context, as each would live in a different habitat, where either sight was an advantage for survival, or with blind animals not required, as there was no advantage in having sight.

I watched a documentary on Darwin last night and they covered the evolution of eyes including the below animal with its impressive ability
https://en.wikipedia.org/wiki/Mantis_shrimp

It would be quite an experience and revelation if we had the visual capabilities of the mantis shrimp. A truly remarkable animal.

Cymek said:

PermeateFree said:

Bubblecar said:

It would be feedback from the visual cortex adjusting the focal length of the lenses (by squeezing or stretching) to reach optimal focus. Part of the huge range of tasks that the CNS attends to without us having to consciously issue instructions. As buffy says, this automatic operation is a product of evolution by natural selection.

There is little point comparing sighted animals with unsighted ones in the above context, as each would live in a different habitat, where either sight was an advantage for survival, or with blind animals not required, as there was no advantage in having sight.

I watched a documentary on Darwin last night and they covered the evolution of eyes including the below animal with its impressive ability
https://en.wikipedia.org/wiki/Mantis_shrimp

Thanks; interesting.