Many researchers have not analyzed the role of dopamine in human evolution, and this topic has therefore received little theoretical attention. Dopamine, which is highly concentrated within the prefrontal cortex, is involved in “high order functioning”. The dopaminergic hypothesis suggests that in the past there were climatic changes in Africa during the Pleistocene and Pliocene periods, and these changes expanded hominin locomotory range. Researchers have also analyzed thyroid hormone production, and found a possible link with an elevation of this hormone and increased dopamine levels.