The generation times of our recent ancestors can tell us something about both the biology and social organization of prehistoric humans. This helps place human evolution on an absolute time scale.
It is generally accepted that current generation times have spanned hundreds of thousands of years or that studies of present-day hunter-gatherer (gatherer) societies provide representative generation times over the course of human history to convert these population genetic estimates into absolute time.
However, neither assumption is likely to be true: while modern hunter-gatherer societies differ significantly from each other and earlier societies, the average age at which men and women have children depends on a variety of environmental, demographic and cultural factors that are rapidly changing. can change. It is also clear that generational times evolved among the great apes and may have evolved along the branch leading to modern humans. Better resolution over time is possible by examining the mutations that arose at specific times in the past, along with a model that accurately predicts the generation times of individuals producing those mutations.
The average age at which men and women gave birth during human development can now be determined by Indiana University researchers using a new technique they devised using DNA mutations. This work could help us understand the environmental challenges of our ancestors. It also helps predict future effects of environmental change on human societies.
Study co-author Matthew Hahn, Distinguished Professor of Biology in the College of Arts and Sciences and Computer Science in the Luddy School of Informatics, Computing and Engineering at IU Bloomington, said: “Through our research on modern humans, we found that we could predict the age at which people had children based on the types of DNA mutations they left their children. We then applied this model to our human ancestors to determine the age at which our ancestors reproduced.”
The study found that the average age at which people have had children over the past 250,000 years is 26.9 years. In addition, fathers were consistently older, averaging 30.7 years, than mothers, averaging 23.2 years. However, the age gap has narrowed over the past 5,000 years, with the most recent estimates of the mother’s age averaging 26.4 years. The shrinking gap is mainly due to mothers having children at an older age.
The scientists found that the age of the parents did not constantly increase over time and may have even decreased some 10,000 years ago due to population growth that coincided with the development of civilization, with the exception of the recent increase in the age of the mother at delivery.
IU postdoctoral researcher Richard Wang said: “These past mutations accumulate with each generation and exist in humans today. We can now identify these mutations, see how they differ between male and female parents, and how they change as a function of parental age.”
Scientists developed a model that uses the spectrum of de novo mutations as a predictor of parental age. Linking this model to variants whose ages have been estimated from genome-wide genealogical information allowed scientists to estimate male and female generation times separately at many different points over the past 250,000 years.
Wang said, “The story of human history is composed of various sources: written records, archaeological finds, fossils, etc. Our genomes, the DNA found in each of our cells, provide a kind of manuscript of human evolutionary history. The findings of our genetic analysis confirm some things we knew from other sources (such as the recent rise in parental age), but also provide a better understanding of ancient human demographics. These findings contribute to a better understanding of our shared history.”
Other study co-authors include Samer I. Al-Saffar, a graduate student at IU at the time of the study, and Jeffrey Rogers of Baylor College of Medicine.
- R. Wang, S. Al-Saffar, et al. Human generation times over the past 250,000 years. Scientific progress. Paper link.