of fruits stimulated some proto-australopithecines to search out new food sources found in the drier savannah ecology. Derek Bickerton (2009) has designated to this period the move from simple animal communication systems found in all great apes to the earliest form of symbolic communication systems capable of displacement (referring to items not currently within sensory perception) and motivated by the need to "recruit" group members for scavenging large carcasses. Homo erectus appeared by about 1.8 million years ago, via the transitional variety Homo ergaster. Calabrian Homo erectus moved from scavenging to hunting, developing the hunting-gathering lifestyle that would remain dominant throughout the Paleolithic into the Mesolithic. The unlocking of the new niche of hunting-gathering subsistence drove a number of further behavioral and physiological changes leading to the appearance of Homo heidelbergensis by some 800,000-600,000 years ago. As such, Homo rose to the ranks of omnivorous predators (and possibly became hypercarnivores before Homo sapiens again transformed into hypocarnivores). As active hunters, they came in opposition to other, quadruped predators and started living in large groups. Homo erectus migrated out of Africa and dispersed throughout Eurasia. Stone tools in Malaysia have been dated to be 1.83 million years old. The Peking Man fossil, discovered in 1929, is roughly 700,000 years old. In Europe, the Olduwan tradition (known in Europe as Abbevillian) split into two parallel traditions, the Clactonian, a flake tradition, and the Acheulean, a hand-axe tradition. The Levallois technique for knapping flint developed during this time. The carrier species from Africa to Europe was undoubtedly Homo erectus. This type of human is more clearly linked to the flake tradition, which spread across southern Europe through the Balkans to appear relatively densely in southeast Asia. Many Mousterian finds in the Middle Paleolithic have been knapped using a Levallois technique, suggesting that Neanderthals evolved from Homo erectus (or, perhaps, Homo heidelbergensis; see below). Monte Poggiolo, near Forlì, Italy, is the location of an Acheulian littoral handaxe industry dating from 1.8 to 1.1 million years ago. The advent of technology and both verbal and non-verbal communication due to transition to group hunting and gathering resulted in the expansion of the parts of the brain associated with these, as well as greater cognition due to it being interlinked with the two. Later, behavioral adaptations to further social life, uncertain food distribution (resulting in need to find and secure food and remember where it could be