Locomotion and Cognition: From fish to hominids

Movement is the first product of the nervous System - is it also its last riddle?

Vertebrate behaviour and cognition seem to have originated in fish.
Every movement of the tail of a fish or of its fins will change the position of the fish in (relation to) its environment. These changes are received by the sense organs: locomotion produces locosensation.
Or in the words of Ragnar Granit: "Muscle moves the world".

Not only our first ancestors were mobile, so, too, were their first life-essential objects: prey, partners, competitors and, perhaps, predators. The cognition of fish has to take note of three moving bodies: itself, its shifting environment and the other animal. The nervous system produces (rhythmic) motor patterns and perceives environmental changes according to these patterns ( figure A).

The next step towards mankind were the tetrapodes. As with fish, their eyes continue to scan the horizon, but the direction of their (loco)motor activity has bent by 90° ( figure B). Reafferent information's are coming from the limbs, additionally. The importance of this internal feedback is that body parts can now move without influencing the environment. Locomotor patterns are thus "fed back" via exafferent patterns (environment shift) and via reafferent sensory patterns.

Primates have four hands to make contact with the arboricole environment. They prefer to sit, moving their arms freely to reach and grasp. Their locomotor apparatus has begun to split:
While seated, the hind limbs and the pelvis are engaged in "nonlocomotion", but the arms and hands bend again by 90° and appear in the frontal visual field (actually this bend developed between head and neck, figure C).

For the first time in the evolutionary process, animals can watch directly and for extended periods of time what parts of their body are doing. Arm and hand motor patterns are also sensed twice: By reafference and by the newly possible visual control. When the nervous system takes notice of the synchronicity in this closed motor-visual loop, the eye-hand complex can develop. Does this indicate that hands, objects which hitherto were known only as parts of the environment, have been "recognised" as parts of the subject? Can we assume that "self- recognition" has taken place?

In hominids the eye-hand-complex permanently works in an autonomous manner. Even during locomotion, arm and hand movements are "movements of their own", independent of the actions of the hind limbs. Tools are now endowed with self-moved quality, throwing extends the distance reachable, the individual can recognise his own shadow and perhaps also his own face moving in a smooth surface of water.