This must surely be what happens when picking blackberries. You see the best ones first, then after you take those, others appear “out of nowhere”. There are spots at all the junctions in the image but “your brain won’t let you see them all at once”. This could be an advantage when many other hands are competing for the best fruit, allowing you to home in on one you’ve identified.
Other ideas I’ve had about evolutionary traits. I don’t know if they are common knowledge anyway:
- The horrible feeling of scratching your nails on a blackboard, which sets your teeth on edge, must be a protection against damaging your teeth or nails on stones when biting or scratching in the ground for food.
- The hypnic jerk (“sleep start”) just before falling asleep, forces you to check that you are not in a position to fall out of bed, or – way back – to fall out of the branches of a tree in which you are nesting.
- The eyelids are the first part to become paralysed on beginning to fall asleep. Could this be to firmly establish shade and so get on with essential sleep?
Stephen Moran's Museum of Illusions 