fecundity

Meaning: In demography, fecundity is the physiological potential to have children, set by factors such as age, health, and nutrition. Fertility is the number of children actually born. Contraception, delayed marriage, personal choice, and social or economic constraints keep actual fertility below fecundity in most populations. (In biology, fecundity can instead mean the number of offspring or eggs an organism produces, which is closer to actual output.)

On the MCAT: Demography passages give a fertility measure, such as the birth rate (births per 1000 people per year) or the total fertility rate, and ask you to explain differences between populations or over time. Fecundity is the contrast term: a population can have high fecundity and low fertility. Typical reasoning questions ask why fertility falls with women's education, urbanization, wider contraceptive access, and lower infant mortality, as in the demographic transition. None of these changes biological capacity. They change how much of that capacity is used.

Common confusion: Students treat fecundity and fertility as synonyms. Fecundity is ability, and fertility is realized births. A falling birth rate therefore does not by itself show that fecundity has fallen. Everyday and medical speech often uses "fertility" to mean the ability to conceive, but demographers use it for actual births, and the exam follows the demographic use.