Brain size

(CC) Photo: University of Wisconsin and Michigan State Comparative Mammalian Brain Collections and National Museum of Health and Medicine (see http://www.brainmuseum.org/)
Comparative anatomy of brains from various vertebrate species, highlighting the gradual differences in brain size and gyrification.

Since the size of the brain has changed considerably during hominid evolution, brain size is a central term in many discussions related to cognitive evolution, intelligence and a number of brain disorders, especially microcephaly. To compare different brains, several indicators of brain size have been used. These include absolute brain size, relative brain size (normalized by body size or weight), and the encephalization coefficient.