Gradual decline

The prime years of adult production and biocultural reproduction last from the onset of adulthood to about age 35 years. Women and men remain vigorous, productive, and fertile after that age but there is a decline of some biological functions and, especially for women, of fertility. In fact, peak fitness in biology, cognition, and fertility is achieved at about age 26 years in people throughout the world. The decline has been measured carefully by human biologists, and may be noted anecdotally by examining the success, and failure, of top-ranked athletes in all sports. The post age 35-year-old decline is noted even in among the most privileged people of the highest income nations. Women over age 35 are less likely to become pregnant and maintain the pregnancy without medical assistance. In lower-income nations, such as Guatemala and Bangladesh, very few women give birth after the age of 35 years. The physical decline with age is gradual during the period from age 26 to about age 50 years. The photographs above capture some aspects of this gradual decline. On the left are Maya women from Guatemala. The grandmother, near 70 years old, is in the center with her daughter, about 55 years, on the right and granddaughter, about age 35, the left of the photograph. The granddaughter and grandmother are depicted in the images in «Families —many sizes and shapes of biocultural kinship». The granddaughter gave birth to three offspring and it is unlikely that she will give birth again. On the right is a Ladina family from Guatemala. The grandmother is in the center of the three taller women, with her daughter to the left and her granddaughter to the right of the photograph. The granddaughter is an adolescent and has not married or given birth. The Maya maid has worked for the three generations of women. She is about the same age as the grandmother. Note the similarity in height of the three Ladina women. As they are close biological relatives, this similarity likely due to both shared genetics and their shared living conditions. The short stature of the Maya maid is typical of Maya women in Guatemala, who are, on average, the shortest women in the world today and have been for the last 100 years. Their very short height is mostly caused by poverty, racism, food insecurity, physical abuse, and other toxic stresses. It is not caused by genetics because Maya families who migrate to the United States produce daughters and sons who become significantly taller than their parents and their siblings who were born in Guatemala. [Barry Bogin]