What is known is that man's great divergence has been in the making of detached, resumable tools.
That is to say, if an insect carries a saw, it carries it all the time. The "next step," as in the case of the male organ of the nautilus, is to grow a tool and detach it.
Man's first inventions are fire and the club, that is to say he detaches his digestion, he finds a means to get heat without releasing the calories of the log by internal combustion inside his own stomach. The invention of the first tool turned his mind (using this term in the full sense); turned, let us say, his "brain" from his own body. No need for greater antennæ, a fifth arm, etc., except, after a lapse, as a tour de force, to show that he is still lord of his body.
That is to say the langouste's long feelers, all sorts of extravagances in nature may be taken as the result of a single gush of thought. A single out-push of a demand, made by a spermatic sea of sufficient energy to cast such a form. To cast it as one electric pole will cast a spark to another. To exteriorize. Sometimes to act in this with more enthusiasm than caution.
Let us say quite simply that light is a projection from the luminous fluid, from the energy that is in the brain, down along the nerve cords which receive certain vibrations in the eye. Let us suppose man capable of exteriorizing a new organ, horn, halo, Eye of Horns. Given a brain of this power, comes the question, what organ, and to what purpose?
Turning to folk-lore, we have Frazer on homed gods, we have Egyptian statues, generally supposed to be "symbols," of cat-headed and ibis-headed gods. Now in a primitive community, a man, a volontaire, might risk it. He might want prestige, authority, want them enough to grow horns and claim a divine heritage, or to grow a cat head; Greek philosophy would have smiled at him, would have deprecated his ostentation. With primitive man he would have risked a good deal, he would have been deified, or crucified, or possibly both. Today he would be caught for a circus.
One does not assert that cat-headed gods appeared in Egypt after the third dynasty; the country had a long memory and such a phenomenon would have made some stir in the valley. The horned god would appear to have persisted, and the immensely high head of the Chinese contemplative as shown in art and the China images is another stray grain of tradition.