Menopause, evolution and changing cultures

Abstract

The menopause is an isolated event in a much wider process that was probably an evolutionary adaptation essential for survival in the Pliocene. As a reproductive strategy, it is largely vestigial in the 21st century, part of an era that has seen a doubling of the average human longevity compared with that of the past. This process commences as an accelerated decline in female fertility, usually from the fourth decade of life, culminating in a total cessation of reproductive capacity for those surviving. The 20th and 21st century sees a huge increase in the numbers surviving and the duration of that postreproductive life phase extending for decades. This extended period of what is essentially a hormone deficiency state is a recent phenomenon and by no means part of the natural history of the human individual. It is therefore not surprising to see a postmenopausal increase in the incidence of so many disorders above that expected by age alone. Recent reproductive patterns have seen increases in the birth rate and requests for fertility treatments among women in their late 30s and 40s. Many try for pregnancy but are unsuccessful. The genes that permit later reproduction and hence later menopause are therefore being preferentially selected. Slowly over generations we will expect to see the fertility of future 40 year olds increase and the age of menopause to extend much later into our, now, longer lives.