I find it hard to believe that people would just band together and volunteer to build things without a monetary (or an equivalent) incentive.

Say, we're at the beginning of the neolithic age, and our village has just discovered agriculture, and the magic of iron ploughs. We already have food supply enough for 6 months.

There's just one small farm left, someone needs to go mine for iron ores, and someone needs to plough the fields, someone needs to sow the seeds.

One person 'volunteers' to do all three tasks because they couldn't agree on who'll do the mining.

The village decides to feed this guy while he does all these things, because he can't hunt while he's working. The 'volunteer' realizes that he could share part of his food with someone else in exchange for some help with iron ore mining and plough-building.

Ok we're now back to the monetary system.