Sex, Equality, and Growth (in that order)

We set up a unified growth model capturing the transition of a primitive and egalitarian hunter-gatherer society, into an advanced and despotic early civilization, and finally into a more egalitarian industrial society. Agents are either landowners or landless; both earn income from human capital, but only landowners earn income from land. The central assumption is that the accumulation of human capital increases with the number of people engaged in intellectual activities, "thinking." For an agent to be a thinker he must be sufficiently rich. At early stages of development, when human capital is scarce, only landowners can afford to think. Human capital thus grows with the size of the landowning class. With polygynous mating, rich landowners attract more women than landless, and thus have more offspring. This leads to a slow expansion in the size of the landowning class and thus a gradual increase in the levels of human capital. At some stage human capital may reach a critical level beyond which also landless agents become thinkers. The set a thinkers then suddenly expands, raising human capital productivity and pushing the economy to sustained growth: an industrial revolution. Allowing also for a quantity-quality trade-off in children a demographic transition sets in. But the economy may also follow a path leading to the downfall of the civilization, and a slow transition back into an egalitarian hunter-gatherer state. Which path the economy follows depends on the level of land productivity. An agricultural revolution is thus a necessary precondition for a later industrial revolution.