Ancient steps in the evolution of human brain and culture
Matz Larsson (Örebro)
Bipedal walking in the evolution of human musical abilities: Why does the hormone dopamine flows when we listen to music, and why don't chimpanzees, our closest primate cousins, have musical ability? Here is hypothesized that the evolutionary switch to bipedalism was crucial. Locomotion produces sound, incidental sounds of locomotion (ISOL). ISOL produced by chimpanzees in treetops or on the ground is irregular and unpredictable, while human bipedal ISOL on flat ground is highly predictable. People of similar length tend to walk in pace. Synchronized ISOL may improve perception of sounds from our surroundings due to glimps-listening (brief interval of silence) and improved auditory grouping. A behavior with survival value tends to produce dopamine. Akin synchronization of movements and similar sound-production may have been rewarding for the brain also in relative safe surrounding; resulting in activities such as hand-clapping, foot-stamping and yelping around the campfire. The step to dance and music may have been short.
The Eye-forelimb (EF)- hypothesis: The primate visual system has a high proportion of ipsilateral retinal projections (IRP) in the optic chiasm (OC). The established explanation is this anatomy results in stereopsis. However, crossing, or non-crossing also determines which hemisphere receives visual feedback in reaching tasks. The EF -hypothesis proposes that abundant IRP developed to synthesize, in a single hemisphere, visual, tactile, proprioceptive, and motor information about a given hand, since that improved eye-hand-coordination. Evidence is that the primate visual system is ideally suited for tasks within the space where the hands operate. In contrast to the stereopsis hypothesis, the EF-hypothesis is applicable on vertebrates in general. It suggests a new perspective on vision convergence in prey and predatory animals.
These hypotheses may have several implications for the study of language evolution.