At the end of the AHP, with increasingly arid conditions, mountain ranges like Tibesti, Tassili-n-Ajjer, and Ahaggar—forming a major topographic feature spanning more than 2,500 km. from southern Argelia to northern Chad—acted as important water towers in contrast to the surrounding plains, providing populations settled on the windward side with more persistent rain runoff. Because of that, some of the earliest direct evidence for the exploitation of domestic livestock, use of milk products, and the construction of cattle tumuli come from the heart of the central Sahara (Brierley, Manning, and Maslin 2018).
The emergence of rock art depicting livestock scenes and stone monuments with associated domestic animal remains in the middle Holocene attest to a highly formalised expression of a wider Saharan “cattle cult”, with isotopic analysis of animal bones from the region demonstrating seasonal transhumance similar to strategies followed by modern traditional pastoralists (Brierley, Manning, and Maslin 2018).
In the Levant, discontinuity in archaeology with the previous period is marked by dramatic changes in settlement patterns, large-scale abandonment of sites, many fewer items with symbolic meaning, and shifts in burial practices, such as secondary burial in ossuaries, which disappear completely. This supports the view of profound cultural upheaval leading to the extinction of whole populations, associated with the collapse of the Chalcolithic culture in the region.
Population replacement is supported in genetics by the genetic discontinuity between the Chalcolithic and the Early Bronze Age period (Harney et al. 2018). Proto-Semites, who probably lived at the beginning of the 4th millennium still on the savannahs of the then still pale-green Sahara, migrated north after ca. 3900 BC, once the region reverted back to a desert climate (Lipiński 2001). Whether they migrated through the horn of Africa to Arabia or through the Nile to the Sinai before reaching the Levant is unclear, although the apparently closer relationship of Proto-Semitic to Proto-Berber, and the appearance of Semitic languages quite early in both the Syrian desert and the Levant, seem to support its initial diffusion through east Africa rather than Arabia.
The presence of haplogroup J1a2a1a2d2-Z1865 (formed ca. 5500 BC, TMRCA ca. 5200 BC) and its subclade J1a2a1a2d2b-Z1853 (TMRCA ca. 4900 BC) in modern south Arabian populations suggests an expansion of this subclade potentially from southern or northern Arabia in ancient times. Subclade J1a2a1a2d2b2-Z2331 (TMRCA ca. 3800 BC) is associated with modern Semitic populations widely distributed through the Middle East, with its oldest subclade J1a2a1a2d2b2a-Y15152 (TMRCA ca. 3800 BC) present today in modern Jewish populations. The presence of J1a2a1a2d2b2-Z2331 subclades later in Canaanites from Sidon (ca. 1750 BC) and in Levant BA from ‘Ain Ghazal (ca. 2100 BC) further supports the connection of this haplogroup with the expansion of Proto-Semitic.
The presence of haplogroup J1a2a1a2d2b2b2c-Z2329 (formed ca. 3600 BC, TMRCA ca. 3600 BC) in a Pre-Ptolemaic Egyptian individual (ca. 670 BC) (Schuenemann et al. 2017) suggests the widespread distribution of this haplogroup J1a2a-L620/Z2356 (formed ca. 16000 BC, TMRCA ca. 12700 BC) along the Levant, from the north to the Sinai Peninsula and beyond, as evidenced by its widespread presence in modern Arabic tribes.
The arrival of Proto-Semitic migrants might have caused the collapse of the related cultures Amratian (Naqada I, in Egypt) and Ghassulian (in the Levant) ca. 3500–3350 BC, both in turn possibly related to Minoans. The expansion of Semites from the Levant may have in turn caused the first split into a western and an eastern dialect, and the further expansion of the latter to the north and east across the Syrian steppes, into south-east Anatolia and southern Mesopotamia.
In northern Arabia, crop cultivation and other features traditionally used to define the Neolithic do not seem to have been practised until the arrival of the Bronze Age (ca. 3000–1200 BC), a situation that contrasts strongly with the Fertile Crescent, where sedentary communities were present since the Epipalaeolithic (Scerri et al. 2018). This significant cultural change also suggests a potential demic diffusion to the region.