Scientists have discovered a new way to identify the average age at which males and females reproduced throughout the history of human evolution.
By studying DNA mutations in modern humans, they discovered a window that allowed them to peek back 250,000 years.
“Through our research on modern humans, we noticed that we could predict the age at which people had children from the types of DNA mutations they left behind in their children,” says the co-author. of the study Matthew Hahn, genomics at Indiana University in Bloomington.
“We then applied this model to our human ancestors to determine at what age our ancestors had children.”
They found that over the past 250,000 years, the average age for humans to have children was 26.9. (For context, 300,000 years ago is also around when our species first appeared.)
The average Homo sapiens the father has always been older than average Homo sapiens mother, according to the study, men become parents at 30.7 years, compared to 23.2 years for women.
But the age gap has narrowed over the past 5,000 years, the researchers add, noting that the most recent estimates from the study suggest the average age at which women become parents is now 28. This trend seems largely driven by women having children at older ages, they suggest.
Aside from the recent increase in maternal age, however, the study found remarkable consistency in the average age of new parents throughout our species’ existence. It has not increased steadily since prehistoric times, the team reports, although it has fluctuated over time.
The average age at conception appears to have dropped around 10,000 years ago, and as this would roughly coincide with the advent of agriculture and the dawn of civilization, the researchers say this could be linked to rapid population growth at the time.
Recorded history only goes back a few thousand years at best, and such population-level information is difficult to glean from archaeological evidence alone.
But the secrets of our ancestors also lurk within each of us today, and that’s how Hahn and his colleagues stumbled upon a way to determine the age of parents so far back in time.
The new study builds on the discovery of de novo mutations – DNA alterations that start in a family member, appearing spontaneously rather than being inherited through the family tree.
While working on another project involving these new genetic changes and relatives of known agethe researchers noticed an interesting trend. Based on data from thousands of children, the pattern and number of new mutations that form in parents before being passed on to their children depends on each parent’s age at conception.
This allowed researchers to estimate separate male and female generation times over 250,000 years.
“These mutations from the past accumulate in every generation and exist in humans today,” says study co-author and Indiana University phylogeneticist Richard Wang.
“We can now identify these mutations, see how they differ between male and female parents, and how they change with the age of the parents.”
Previous research has also used genetic indices to estimate generation time over time, but has generally relied on comparisons between modern DNA and ancient samples that have been averaged across sexes and over time. 40,000 to 45,000 years ago, the researchers note.
“The history of mankind is reconstructed from a diverse set of sources: written documents, archaeological finds, fossils, etc.,” says Wang.
“Our genomes, the DNA present in each of our cells, offer a kind of manuscript of the history of human evolution.
“The results of our genetic analysis confirm some things we knew from other sources, but also offer a richer understanding of the demographics of ancient humans.”
The study was published in Scientists progress.