The amygdala, a brain area involved in associative learning, value encoding, and emotional responses, was particularly important.
However, although smokers indicate that they smoke for stress relief and relaxation, some research suggests that smoking increases subjective stress levels and that smoking does not lead to stress relief but merely reverses the negative mood state caused by nicotine deprivation (Parrott, 1999). Stress levels of smokers vary widely throughout the day. Smokers have decreased subjective stress levels immediately after smoking a cigarette and increased stress levels between cigarettes when nicotine levels are low
In other words, a diversity of hominin species once existed. Our tree was “bushy”. In the time before 2 million years ago, we haven’t yet found any fossil trace of hominins anywhere other than Africa. Our lineage had an African origin, it had a diversity of adaptations to ancient African environments, and for two thirds or more of this history, it appears that our ancestors and relatives were exclusively African.