Brain
There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. Serotonin, for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei. Norepinephrine, which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus. Other neurotransmitters such as acetylcholine and dopamine have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.
Evolution of nervous systems
There has been a gradual increase in brain volume as the ancestors of modern humans progressed along the human timeline of evolution (see Homininae), starting from about 600 cm in "Homo habilis" up to 1736 cm in "Homo neanderthalensis". Thus, in general there is a correlation between brain volume and intelligence. However, modern "Homo sapiens" have a smaller brain volume (brain size 1250 cm) than neanderthals; women have a brain volume slightly smaller than men, and the Flores hominids ("Homo floresiensis"), nicknamed "hobbits", had a cranial capacity of about 380 cm, about a third of the "Homo erectus" average and considered small for a chimpanzee. It is proposed that they evolved from "H. erectus" as a case of insular dwarfism. In spite of their threefold smaller brain there is evidence that "H. floresiensis" used fire and made stone tools as sophisticated as those of their proposed ancestor, "H. erectus". Iain Davidson summarizes the opposite evolutionary constraints on human brain size as "As large as you need and as small as you can".