Public interest in social and economic equality is burgeoning. In a recent paper in PNAS that examines both nonhuman primates and humans, we measured a related phenomenon, lifespan equality – a measure of whether lifespans in a population tend to vary a lot or be similar to each other. We used data from six well-studied primate populations – our own Amboseli baboon population, and also mountain gorillas in Rwanda, chimpanzees in Gombe Stream National Park in Tanzania, sifaka in Beza Mahafaly in Madagascar, muriqui monkeys in the RPPN Feliciano Miguel Abdala in Brazil, and capuchin monkeys in Santa Rosa National Park, Costa Rica. Read More
Surviving infancy is challenging for wild primates, as decades of research on species ranging from lemurs to gorillas have revealed. For an infant baboon, surviving the first year of life requires learning to identify and successfully consume more than 250 types of food, avoiding fatal disease and predation, and perhaps most importantly identifying and avoiding dangers from other baboons both inside and outside their social group. In Amboseli, first-year mortality has averaged about 30 percent over the four decades of our study, but has climbed as high as 50 percent during difficult times. Just getting through infancy represents a huge piece of the Darwinian gauntlet that every animal must run.
In humans and other animals, harsh circumstances in early life are linked to poor health and high mortality rates in adulthood. It is thought that these effects are greatest when multiple adverse conditions occur at the same, but this hypothesis has rarely been tested. We used prospective data on 196 wild female baboons in Amboseli to show that the number of adverse circumstances that a female experiences during her juvenile years predicts how long she lives as an adult. Specifically, we examined the effects of six different adverse circumstances: (i) being born in a drought, (ii) having a low ranking mother, (iii) having a socially isolated mother, (iv) having your mother die before you reach 4 years of age (the approximate age at sexual maturity for females), (v) having a younger sibling born when you yourself are still quite young (1.5 years of age or less), and (vi) living a very large social group. Females who experience 3 or more of these adverse circumstances tend to die 10 years earlier than females who experience no adverse circumstances. For comparison, the average female, once she reaches adulthood, lives to about 18.5 years of age, so 10 years is a very large difference in the life of a female baboon.