How do we know? Thanks to scientists, some fantastic detectives of the past, who try to unravel a process that took place along hundreds of thousands of years. We still need know a lot, but every time we understand a little more how mankind was formed.
Today's humans are all a consequence of evolution, which is the process of transformation of species through changes produced in successive generations. We belong to the group of vertebrates, to the class of mammals, to the order of primates, to the Homo species and to the genus Homo sapiens.
But the evolution of each species was different. We all probably come from a common trunk that, way back, 70 million years ago.