A Series of Eyes
How do we see? In the 19th century the anatomy of the eye was known in great detail, and its sophisticated features astounded everyone who was familiar with them. Scientists of the time correctly observed that if a person were so unfortunate as to be missing one of the eye's many integrated features, such as the lens, or iris, or ocular muscles, the inevitable result would be a severe loss of vision or outright blindness. So it was concluded that the eye could only function if it were nearly intact.
Charles Darwin knew about the eye too. In the Origin of Species, Darwin dealt with many objections to his theory of evolution by natural selection. He discussed the problem of the eye in a section of the book appropriately entitled "Organs of extreme perfection and complication." Somehow, for evolution to be believable, Darwin had to convince the public that complex organs could be formed gradually, in a step-by-step process.
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