Demographic Transition - Stage Five And/or Six

Stage Five And/or Six

See also: Aging of Europe, Aging of Japan, and Evolutionary psychology

The original Demographic Transition model has just four stages, but additional stages have been proposed. Both more-fertile and less-fertile futures have been claimed as a Stage Five.

Some countries have sub-replacement fertility (that is, below 2.1 children per woman). This should be 2.1 because it replaces the two parents, and adds population for deaths with the added .1 child. European and many East Asian countries now have higher death rates than birth rates. Population aging and population decline may eventually occur, presuming that sustained mass immigration does not occur.

In an article in the August 2009 issue of Nature, Myrskyla, Kohler and Billari show that previously negative relationship between national wealth (as measured by the human development index (HDI)) and birth rates has become J-shaped. Development promotes fertility decline at low and medium HDI levels, but advanced HDI promotes a rebound in fertility. In many countries with very high levels of development fertility rates are now approaching two children per woman — although there are exceptions, notably Germany and Japan.

In the current century, the past decade as of 2012, most advanced countries have increased fertility. This is completely expected from the viewpoint of evolutionary psychology, with drastic environmental changes causing selection of behavioral traits that increase reproduction.