We are members of a large and noisy family called the great apes. 6 million years ago, a single female ape had two daughters. One became the ancestor of all chimpanzees, the other is our grandmother.
Biologists label organisms with a two-part Latin name, genus followed by species:
families > genus > spices.
For example, lions, tigers, leopards, and jaguars are different species within the genus Panthera.
The genus Homo evolved from an earlier genus of Apes called Australopithecus. However, the most important thing to know about prehistoric humans is that they were insignificant animals with no more impact on their environment than gorillas, fireflies, or jellyfish.
Humans had extraordinarily large brains compared to other animals. Modern Homo sapiens sport a brain averaging 80 cubic inches, but Neanderthal's brains were even bigger and also more muscular — which disproves that natural selection favored intelligence.
It did, though, favor earlier births. And, indeed, compared to other animals, humans are born prematurely. Raising children required constant help from other members. Evolution thus also favored those capable of forming strong social ties.
From about 2.5M years ago until around 10K years ago, the world was home to several human species. Very much like today, there are many species of bears: brown bears, black bears, grizzly bears, polar bears.
We are used to thinking about ourselves as the only humans, but there were up to 6 different Homos for a long time — of course, all of them human.
The question is: why? There are two competing theories:
It turns out we share a small percentage of genetic code with Neanderthals and Denisovans, which suggests that both theories could be right. 50k years ago, Sapiens, Neanderthals, and Denisovans were almost, but not quite, entirely the same species. We were not completely different species, like horses and donkeys; but also, not just different populations of the same species, like bulldogs and spaniels.
❓ "The" question: what would have happened — from a societal point of view — if other human species were still around?