My own hypothesis is walking not only freed our hands, but also freed our mind. The human are the rare if not only species relies heavily on remote projectiles for attack. Most other animals are melee main. (I happy to be proven wrong)

Now the fun part. If you are melee main, you just out-run your food and bite them, simple. However, to master remote attacks, you must predict how the prey moves. You have prepare carefully, plan how your projectiles fly, or else you get nothing.

This enforces us to mimic other animals, the better we think like the prey the better we catch our food or avoid big monsters. This is how primitive animal worship originates. Those who understands animals best are the most wise person in tribes.

This also give us apathy and self-awareness, and ultimately, the consciousness, and it catalyze our social structure, because collaboration makes hunting much more efficient. This motivates our ancestors to evolve as a group.

Projectiles gave us an artificial world with a beauty of its own. Parabola is studied extensively throughout history.

A species's food source depending on ultilizing projectiles think differently than other animals. Bipedalism hominins are meh, but bipedalism hominins having stones in their hands are extremely dangerous.

(Btw, are there any books or papers supporting my idea?)