Generationsperioden

Generationsperioden, også kaldet generationstid, refers to the average interval between the birth of parents and the birth of their offspring in a given population. It is typically measured in years and is used in demography and population genetics to describe the tempo of generational turnover.

There are several ways to define and calculate generationsperioden. The most common definition is the mean age of parents at the birth of their child, often expressed as the average age of mothers at birth. A related approach is a weighted average of parental ages at birth across all births in the population, which accounts for the age structure and birth rates of different age groups.

The concept is important because it connects mutation rates, which are often stated per generation, to rates per year, and it informs models of population growth and evolutionary dynamics. Generationsperioden also reflects social and demographic factors such as fertility timing, age at first birth, and changes in life expectancy and age structure.

Typical values vary widely between species and populations. In humans, generation time is generally in the range of 25 to 30 years, with many contemporary populations around 28 to 30 years. Historical periods with earlier childbearing tend to have shorter generation times, while modern societies with delayed childbearing tend to have longer times. Limitations include that generationsperioden is not fixed; it differs by cohort, region, and method of calculation, so precise estimates depend on the data and definition used.