The second demographic transition: A concise overview of its development: Table 1.

At the end of the historical declines in both mortality and fertility (the "first demographic transition"), new demographic phenomena developed in the Western World. Therefore, new theoretical frameworks were needed to explain features such as the baby bust, the systematic postponement of marriage and parenthood, subreplacement fertility, the rise of alternative forms of partnerships, and parenthood outside marriage. The "second demographic transition" (SDT) theory is such an attempt. Although it accepts the major tenets of bounded rational economic choice, it also allows for autonomous preference drift by relying on Maslow's theory of shifting needs. As such, an essentially cultural component is being added.