The most important error in his theory, to my mind, is that it ignores intelligence as a cause. Men and apes, in the same environment, have different methods of securing food: men practice agriculture, not because of some extra-human dialectic compelling them to do so, but because intelligence shows them its advantages. The industrial revolution might have taken place in antiquity if Greek intelligence had remained what it was at its best. To this it is customary to reply that slave labor, being cheap, removed the incentive to the invention of labor-saving devices. The facts do not bear out this view. Modern methods of production began in the cotton industry, no only in spinning and waving, which employed “free” labor, but also in the gathering of cotton, which was the work of slaves. Moreover no slaves were ever cheaper than the wretched children whom the Lancashire manufacturers employed in the factories of the early 19th Century, where they had to work 14 or 16 hours a day, for little more than board and lodging, till they died. (It must be remembered that the death of a slave was an economic loss to his owner, but the death of a wage-earner is not.) Yet it was these same ruthless employers who were the pioneers of the industrial revolution, because their heads were better than their hearts. Without intelligence, men would never have learnt to economize hand labor by the help of machines.
I do not wish to suggest that intelligence is something that arises spontaneously, in some mystical uncaused manner. Obviously it has its causes, and obviously these causes are in part to be sought in the social environment. But in part the causes are biological and individual. These are as yet little understood, though Mendelianism has made a beginning. Men of supreme ability are just as definitely congenitally different from the average as are the feeble-minded. And without supreme ability fundamental advances in methods of production cannot take place.
Russell, Bertrand. Understanding History. New York: Philosophical Library, 1957