In discussing Richard Longhurst’s model of the energy trap in the previous chapter, we speculated that differences among households in nutritional status could be amplified, via their effects on work capacity, into semipermanent, inter-generational differences in a family’s material well-being. But the energy trap, if it is to operate at all, must act on preexisting differences in household well-being. Thus far, we have said nothing about where those initial differences come from. A large part of the answer, of course, is that traditional farmers, like all people, vary among themselves in such things as industriousness, cleverness, prudence, fecklessness, even sheer dumb luck – not to mention the political nous to turn a temporary advantage into something more enduring. In addition, environmental unpredictability can be a potent source of differential household success, even in communities that appear to us to be egalitarian. In this chapter, however, we focus on one possible source of economic differentiation that is inherent in the household demographic enterprise – the household’s built-in demographic life cycle, the ebb and flow of household size and age–sex composition resulting from births, deaths, marriages and other forms of inter-household migration (see Chapter 7). More specifically, inter-household differentiation arises from two facts: (i) that the life cycles of all the households in a community are never in perfect synchrony, and (ii) that an element of randomness always plays a part in every household’s life cycle. No two life cycles are ever quite the same in their intensity and timing – and these dissimilarities can have important economic consequences.