Where it all began:
Fossil evidence of proto-apith habitation on the African savannahs link semi-bipedal apes living 3.5 million years ago to species homo.

The hominid remains discovered at Laetoli, near Olduvai Gorge, place Australopithecus afarensis at the branching-off of our most distant forbears. Mary Leakey discovered a track concreted in volcanic ash at Laetoli. Dated at 3.7 mil yr b.p. The family unit; two adults, and a child treading in one's footsteps; positively demonstrated upright walking. Here, too, of similar antiquity, the skeleton of an individual nicknamed Lucy, whose limbs showed a fully bipedal gait, yet the hands and feet were still adapted for significant arboreal activity.

Era	Period	Epoch	Age of	Yrs. B.P.	Headlines
Cenozoic	Quaternary	Holocene	Bronze	40,000-10,000	Early Civilizations
			Neolithic	200,000-40,000	Fired pottery
			Mesolithic	1 million-200,000	Bi-facial stone tools
			Paleolithic	2-1 million	Crude stone chopping tools
	Quaternary	Pleistocene		3 million	Magnetic reversal, species homo
	Tertiary	Pliocene		12-3 milion	Demise of dinosaurs
		Miocene		26-12 million	Global cooling
		Oligocene		37-26 million
		Eocene		53-37 million
Cenozoic	Tertiary	Paleocene		65-53 million	Heated volcanic atmosphere

The terrain of rift valleys on the plateaux of Tanzania and Ethiopia, the mild climate and abundant food sources, all combined to make evolution of s. homo a long, slow process.

The stagnation of our relatives in those distant times is proved through the fossil record, which in fact, separates h. erectus from early stone tools by 1.6 mil. years.

In his book Timewalkers Clive Gamble demonstrates how the impetus for h. sapiens sapiens' accelerating colonization of the planet was inspired by a cultural phenomenon which made us different from other apes: a cadre of adolescent males scouted in widening circles for new food sources, and brought food back to the females at a base camp.

Fluctuations in global climate occurred over millenia, and gross changes in an area's food productivity would then send the clan looking for new territory.

So, a few tribes of eligible mating partners tentatively extended their habitat farther and farther from the easy street of sub-Saharan Africa. As they went they met with increasing competition for resources. Eventually our progenitors had colonized most of Africa, mid-latitude Asia, and Europe.