Yesterday People
Thanks to Jill, Rhea and Cath for your help.
Evolution.
It's a marvellous process, very hit and miss, mostly miss.
For example, suppose that you're one of many creatures, all living in a cave. This cave is deep underground. So deep that no light reaches it. Now let us suppose that a few of your number have developed light sensitive cells on their foreheads. A completely useless trait in your pitch black environment.
Now let us suppose that, through some happenstance, light is introduced into your cave. Whether that be by an external influence or by some other event is not important to our example. The important point is, those who can see now have a potential advantage.
But there's the catch; this potential will only become an advantage if their reactions to and comprehensions of their world can be informed by this new sense. Otherwise it would be as useful as schizophrenia to a bus driver.
If.
If the gods of evolution are kind enough to provide the light - a lighthouse, a beacon in the dark. Then, given this new sense of orientation, a being's comprehension of their world would be greater. Their horizons would be expanded.
Where would that leave the rest of us, all pawing about in the dark?