Final answer:
Homo erectus brain sizes averaged between 1,000 and 1,200 cc, denoting a significant increase in size compared to their predecessors and enabling advanced behaviors.
Step-by-step explanation:
Although variable, Homo erectus brain sizes on average were about 1,000 to 1,200 cubic centimeters (cc). This species showed significant evolutionary increases in brain size compared to earlier hominins, which enabled them to create more complex tools, adapt to their environments, and possibly develop early forms of communication. Despite not being as large as the brains of Neanderthals or modern humans, the brain size of Homo erectus was impressive given the context of their place in human evolution. It's also important to note that brain size is not the sole determinant of cognitive abilities, as evidenced by archaic Homo species and Homo floresiensis, which both demonstrated sophisticated behaviors despite smaller brain volumes compared to Homo erectus.