Bats have eyes but they have poor vision. This is because they are nocturnal and they live in caves, (like Batman). So their eyes have adapted to the darkness of the cave. If they were to go out at night the brightness of the moon would be like a flash from a camera to them. They'd need sunglasses, or moonglasses! These are expensive to make for bats and they'd fall off and break as they hung upside down from trees.
So over the years the bats have adapted through evolution and their eyes are suitable to see when in the caves but they use their ears, (sound/sonar) for guidance when out flying at night.
Deep under the sea it is very dark. So how do fish see and not bump into each other? Glasses are of no use to them because they'd get wet and you can't see through wet lenses.
Like bats, their eyes have evolved to detect a lower number of photons (bits of light) so they see the darkness as light. If you were to lift a fish from deep down up to the surface the chances are it will be in agony and go blind because of the light up here on the surface. More photons per square metre than deep down in the sea. So, unlike bats, these fishes have decided to stay at the bottom of the sea and not come up to the surface or hang upside down from trees.
And whilst we're talking about water; did you know that humans cannot feel wet? We can't feel the sensation wet. If you blindfold someone and give him two sets of clothing, one wet/damp and one cold he could not tell the difference by touch. (Not wringing or squeezing - just touching). The human skin can feel cold and hot. Not wet. Admittedly if you put your hand in a bowl of water you'll feel it - but this is feeling the existence of water not feeling the wetness. And if someone's asleep and you put his hand in a bowl of water he'll feel wet - but that's different.
And finally ... we've talked about darkness here - in caves as well as deep in the bottom of the sea. But in reality, there is no such thing as darkness. Darkness is the absence of light. Remember that next time you stub your toe against something in the dark; or you fall over on the way home at night from the pub.
“I am the light of the world. Whoever follows Me will never walk in the darkness, but will have the light of life.” John 8:12
NOTE: If there is anything else scientific, or religious, you wish me to explore and write about here then please let me know.
