By definition, the free market is reality. Willing buyers, willing sellers, and a “relatively” free flow of information that affects prices. Since the dawn of mankind, it is the best system yet devised to allocate capital for the highest and best use, and for creating wealth.
We know that philosophically and intuitively but there's archeological evidence of that too. Neanderthal digs showed groups of beings with organized families and teams, they used tools, and they even buried their dead with respect and honor. A big difference between them and the first modern people (aka 'Cro-Magnon') was that these new sites would also have things that came from many hundreds of miles away --obsidian, rare hides, etc. in contrast to the Neanderthal's use of only whatever they found outside.
You nailed it, commerce began at the dawn of mankind.