To live longer, nerve cells need to understand what’s going on around them. Therefore, they generated an extension that ends with receptors capable of transforming light into a nerve impulse. The nerve impulse through the extension reaches the nerve cells, which process it in order to understand it, and then determine the organism’s behavior based on what is understood. This is the function of the visual apparatus where the receptors (cones and rods on the retina) transform the photon into a nerve impulse which, through the optic nerve and other structures of the brain, reaches the occipital lobe where it is processed and made understandable for the brain.
But it was not enough. The nerve impulse generated by the eye must be able to shape the brain on the characteristics of the environment, to improve the individual’s adaptation to the environment. With the imprinting mechanism, the eye does not just perceive, but changes the brain, on the base of precise visual stimuli. As in the duck, which follows the first object that sees moving in the sensitive period of its growth. In this case, the eye not only provides information to the brain, but, in some way, it changes it, inducing irreversible behavior based on visual stimuli.
In Homo Sapiens the whole brain is structured on what is perceived by the eye and the other senses during childhood, so that the human being can better adapt to the cultural environment in which he lives. Environmental changes lead to cultural changes in new generations: this is the engine of cultural evolution.