 The "relative income" theory explains the baby boom by suggesting that the late 1940s and the 1950s brought low desires to have material objects, because of the Great Depression and World War II, as well as plentiful job opportunities (being a post-war period).These two factors gave rise to a high relative income, which encouraged high fertility.Following this period, the next generation had a greater desire for material objects, however, an economic slowdown in the United States made jobs harder to acquire.