[mmartin798]

While I do not have 4th edition, I can venture a guess. Since active and efficient livestock and aquaculture, i.e. cattle ranching and fishing, gives a good amount of food for a smallish investment of human labor you get more man hours for things like manufacturing and the like. Therefore, you get a multiplier for those. But it is just a guess.

Ok, a little more explanation of my guess may be in order. A tribe of people need to expend a certain amount of effort procuring basic food, water and shelter. If the activities they use are really bad hunter/gatherer, then all their work goes into that and nothing for economic growth. So Frank, Tom, Harry, Lisa and Mary are a tribe and all are out gathering food and can only serve their needs. Let's say Frank learns to Fish and does so very well. Now Frank is able to get enough food so that Harry and Lisa don't have to do anything for the tribe to survive. This lets Harry and Lisa to start making and stringing clay beads into jewelry. Now they have something the tribe can trade because Frank is able to fish and feed more of the tribe. Does that help at all?