Not being a student of history, its often difficult for me to locate important events on a timeline and to see their relative importance and why they may have an influence on our lives today. The hypothesis that humans have a single origin was published by Darwin in 1859. There is significantly more evidence to support this theory today, apparently hominids diverged from chimpanzees 5-7 million years ago and a discovery within the last decade puts this nearer the earlier date. Modern humans, Homo Sapiens evolved in Eastern Africa 200,000 to 140,000 years ago and using genetic testing a much more accurate map of human ancestry and migration to all inhabited parts of the world is now available.
Apparently there is still much academic debate, which occasionally spills over to mainstream media, regarding the Recent African Origin (RAO) model. Around 60,000 years ago a group of 150-200 early humans made it out of Africa and proceeded to populate the rest of the planet. Ultimately surviving all earlier hominids that had journeyed out of Africa previously. Looking at the timeline at the top, in the last 800,000 years (80% of the last section of the 7) there were eight ice ages, each interspersed with warmer periods of around 10,000 years. The impact of the extreme cold on the planet does not only have the obvious effect, that of the ice sheets advancing across the northern hemisphere cutting off vital resources for these hunter gatherer communities, but also the locking up of water in these sheets meant that lower rainfall turned half the land between the tropics into desert. A torrid time then for the human race. About 12,000 years ago the last ice age was drawing to an end - temperatures rose, vegetation returned and animals spread into the former wastelands. The hunters followed. By this time in the Near East and Central America these humans had begun to develop new ways of producing food, farming had started. During the 150,000 years that preceded this time, modern humans numbered only in their millions and had migrated the globe foraging and hunting in small groups. This fundamental change in human behaviour signalled the start of the transition to modern society.