Dialectics and its study was derived from Hegel who had studied the Greek philosopher Heraclitus. Heraclitus taught that everything was constantly changing and that all things consisted of two opposite elements which changed into each other as night changes into day, light into darkness, life into death etc.
Most of the work is fragmentary, but it has points of interest. In biology, he says:
Vertebrates. Their essential character: the grouping of the whole body about the nervous system. Thereby the development of self-consciousness, etc. becomes possible. In all other animals the nervous system is a secondari affair, here it is the basis of the whole organisation.
