ABSTRACT
The human eye tells us what we can recognize. It was easy in the past to recognize plants and animals. Plants did not move about except when growing in water. Animals moved about a lot, whether in water, on the ground, or even in the air. From the beginning of life on earth, the eye has served as the prime detector of life by observation of movement. This reliance on sight reached the point where anything that could not be seen was considered not living! Until 200 years ago, visibility was the basic premise upon which life was recognized: if you could not see it, it could not be alive.
