‘In every species, eye and ear respond to stimuli from remote objects, but the interest of animals is limited to the proximate. Their attention is caught by that which is within the confines of reaching or approaching. The relation of sight and bite distinguishes the human face from those of lower animals. Animal jaws, snoot, trunk, and beak–all of them organs acting in the direct contact of grasping and gripping–are placed in the "visor line" of the eyes. With upright posture, with the development of the arm, the mouth is no longer needed for catching and carrying or for attacking and defending. It sinks down from the "visor line" of the eyes, which now can be turned directly in a piercing, open look toward distant things and rest fully upon them, viewing them with the detached interest of wondering. Bite has become subordinated to sight.’"

Also:  Ibid, pages 71-2 (subquote again is from Erwin Straus, "The Upright Posture," in "Phenomenological Psychology," 1966):

"Though man remains a nourishing being, we now see clearly that his being-in-the-world is oriented not solely or even primarily as eater.  He is, by natural attitude, a being whose eyes are encouraged to be bigger than his stomach.

'Animals move in the direction of their digestive axis.  Their bodies are expanded between mouth and anus as between an entrance and an exit, a beginning and an ending.  The spatial orientation of the human body is different throughout.  The mouth is still an inlet but no longer a beginning, the anus, an outlet but no longer the tail end.  Man in upright posture, his feet on the ground and his head uplifted, does not move in the line of his digestive axis; he moves in the direction of his vision.  He is surrounded by a world panorama, by a space divided into world regions joined together in the totality of the universe.  Around him, the horizons retreat in an ever growing radius.  Galaxy and diluvium, the infinite and the eternal, enter into the orbit of human interests.'

"As with upright posture itself, the contemplative gaze–or the transformation of seeing into beholding–requires maturation, and especially inner or psychic growth; small children do not have it and remain largely interested only in things that lie within their grasp.  Eventually, as adults, we are able to organize the visible world into things near and far or, alternatively, into those visible and even remote things we are interested in prehending (by bringing them near) and those we are content to let be and to comprehend, at a distance and in their place, against a background totality, a world."