One would expect, then, that the evidence for the increasing complexity of the prehistoric cultural record would be linked to an increase in brain size of the associated prehistoric hominids. Researchers can assess brain size and the form of limbs and feet of prehistoric specimens to see what they can tell us about the course of human development.
It is much less easy, however, to tell such things as whether or not the prehistoric creatures in question had lost their fur coatings yet or whether they had developed the capacity for articulate speech.
In the 4th century BC, the Greek philosopher Plato somewhat flippantly defined "man" as an erect and featherless biped.
Subsequently Diogenes the Cynic, in an equally flippant fashion, displayed a plucked chicken and declared, "Here is Plato's man." Plato's student, Aristotle, also was concerned with verbal definitions and distinctions, but he went on to describe the natural world in a matter-of-fact fashion that has earned him recognition as the founder of the biological sciences.
Much later, in the middle of the 19th century, Charles Darwin, in his brilliant book 'On the Origin of Species by Means of Natural Selection' (1859), forced the world to face the fact that all the living creatures of the world had almost certainly descended from a common ancestor.