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From time to time, curious people, both young and old, ask the question “when did humans show up in the history of the world?” That’s a great question, but the answer is complicated and experts still are not certain about exactly how human evolution unfolded. A good place to start is the recently refined definition of hominids and their family tree, which includes modern human beings and several extinct ancient species plus their direct ancestors. Hominids originated during the Pliocene epoch, which began 5.3 million years ago, and is celebrated by the presence of the first primates who stood erect. This important discovery was made in 1974 by paleoanthropologist Johanson et al. [1] in Ethiopia, and included the spectacular finding of the nearly intact skeleton of a 3-foot-plus tall young adult female, who was promptly named Lucy and became widely famous. Four years later, Mary Leakey [2] discovered similar bony remains and numerous prehumen footprints more than 1,000 km away in Tanzania. Today, nearly 400 specimens of Australopithecus afarensis have been studied and securely dated from 3.9 to 3.0 million years ago.

A major transition from prehuman to human hominids occurred a few million years after the onset of the Pleistocene epoch, or last Great Ice Age, 2.6 million years ago. The new descendants were the first humans who warranted the name “Homo,” which means “man,” and were designated Homo habilis, or “Handy Man” [3]. H. habilis had both ape-like physical features and manner of walking, but the species knew how to make and use primitive stone (mainly flint) tools. Within the next half a million years or so, Homo erectus appeared showing off its human-like body and larger brain; moreover, it walked fully upright and probably could run [4]. H. erectus originated in Kenya and Tanzania in sub-Saharan Africa, but then migrated widely in Eurasia and as far away as Indonesia. A talented species, H. erectus invented specialized stone tools and weapons, hand axes, clubs, awls, harpoons, and cleavers. Though there was competition over who won the contest, H. erectus is often credited as discovering “the controlled use of fire.” Other precursor human species are known but less well characterized. Archaic Homo neanderthalensis, evolved more than 350,000 years ago and achieved “full-blown” structure 130,000 years ago [5]. H. neanderthalensis had genetic similarities with Homo sapiens, but was shorter, stockier, and had similar or even larger cranial cavities and brains [6]. Until becoming extinct around 30,000 years ago, H. neanderthalensis overlapped in time with H. sapiens, and DNA evidence suggests they may have interbred with modern humans.

The sole surviving species of humans, H. sapiens, first appeared in Africa around 200,000 years ago, but remained geographically isolated for the first 100,000 or so years, possibly owing to the prevailing and always menacing climatic upheavals. New evidence suggests up to 300,000 years ago [7]. Their predecessors, probably H. erectus, had migrated out of Africa “during a warm interglacial period,” between 130,000 and 80,000 years ago in the Near East, which was subsequently taken over by Neanderthals [8]. Paleo archaeologists are not certain exactly when, but once the opportunity opened up, probably because the climate mellowed a little, successive waves of migration took place, which was called the Great Expansion [8]. Not long before and then accompanying the earliest migrations – the newly established time table estimates that around 70,000 years ago, M. tuberculosis began to infect and cause TB in H. sapiens – initially in Africa, then in Eurasia [9].