Back in 1977, Sagan delved into the 3-layer evolution of the mammalian brain over the last 100 mn years. A worthy attempt to unravel the most complex biological assemblage (per kilo) yet known.
Sagan is somewhat simplistic in the way he stresses the layering (neocortex), reptilian core etc.. instead of increases in interconnectivity & his theorising may no longer be accurate in the 21st century. He depicts the Homo Sapiens brain as an organ riven with inner conflict & adversarial hangovers.
Hence the age-old dragons slain & re-slain (presumably our collective DNA memory of nocturnal mammal v. dinosaur?)
Very entertaining popularisation of science nonetheless.