“Some
very simple animals have nothing more than light sensitive spots, that
enable them to tell the difference between light and dark. But if a
patch of such spots formed in even the shallowest of pits, one edge of
the pit would throw a shadow and so reveal the direction of light. If
the pit got deeper and started to close, then light would form a blurred
image. Mucous secreted by the cells would bend the light and focus it.
If this mucus hardened it would form a proper lens and transmit a
brighter and clearer image.
All these different, fully
functional, stages at different levels of complexity are found in living
animals today. Some single-celled creatures have one of those
light-sensitive spots. Flatworms have a small pit containing light
spots, so they can detect the shadow of a predator. A snail’s blurry
vision is good enough to enable it to find its way to food. And the
octopus has an eye with a proper lens and can see as much detail as we
can. So the structure of the human eye does not demand the assistance of
a supernatural designer. It could have evolved gradually, with each
stage bringing a real advantage - as Darwin’s theory demands.”
► David Attenborough
All these different, fully functional, stages at different levels of complexity are found in living animals today. Some single-celled creatures have one of those light-sensitive spots. Flatworms have a small pit containing light spots, so they can detect the shadow of a predator. A snail’s blurry vision is good enough to enable it to find its way to food. And the octopus has an eye with a proper lens and can see as much detail as we can. So the structure of the human eye does not demand the assistance of a supernatural designer. It could have evolved gradually, with each stage bringing a real advantage - as Darwin’s theory demands.”
► David Attenborough
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