Science Advances: The average age at conception for men and women over the past 250,000 years

Generation-specific research can tell us a lot about human biology and social organization
.
Now, researchers at Indiana University have developed a new method using DNA mutations that can determine the average age at which women and men have children in human evolutionary history
.

The researchers say the work can help us understand the environmental challenges our ancestors experienced, and it can also help us predict the impact of
future environmental changes on human society.

"Through our study of modern humans, we noticed that we can predict the age at which people have children based on the type of DNA mutations they leave to their children," said study co-author Matthew Hahn, "and then we applied this model to our human ancestors to determine at what age our ancestors gave birth
.
" ”

According to research published in Science Advances, co-authored by Indiana University postdoctoral researcher Richard Wang, the average age at which humans have children over the past 250,000 years has been 26.
9 years
.
In addition, the average age of fathers is 30.
7 years, which has always been older than the average age of mothers (23.
2 years), but this age gap has narrowed over the past 5,000 years, with the study's latest estimate of the average age of mothers being 26.
4 years
.
The main reason for the narrowing of the gap seems to be the mother's older
childbearing age.

The researchers found that, with the exception of the recent rise in maternal childbearing age, the age of parents did not increase steadily compared to the past, and may have declined about 10,000 years ago, as population growth coincided
with the rise of civilization.

"These mutations from the past accumulate in each generation and are present in humans today, and we can now identify these mutations to see how they differ between male and female parents and how they change with the age of
the parents.
"

The DNA that children inherit from their parents contains about 25 to 75 new mutations, which allows scientists to compare parents and offspring and then classify
the types of mutations that occur.
While looking at mutations in thousands of children, Indiana University researchers noticed a pattern: The type of mutations a child acquires depends on the age
of the mother and father.

Previous genetic methods for determining the timing of historical generations relied on the compounding effect
of recombination or mutation of modern human DNA sequences that differ from ancient samples.
But the result is an average of
men and women over the past 40,000 to 45,000 years.

Hahn, Wang and their co-authors built a model to estimate the generation time
of males and females over the past 250,000 years using de novo mutations (a genetic alteration that first appears in a family member due to a mutation or mutation in one parent's germ cells, or in a fertilized egg during early embryogenesis).

The researchers did not initially want to understand the relationship between sex and age when pregnant; They are conducting a broader investigation
into the number of mutations parents pass on to their children.
They only noticed age-based mutation patterns, while trying to understand the similarities and differences
between humans and other mammals such as cats, bears, and macaques.

"The story of human history is pieced together from a range of different sources: written records, archaeological finds, fossils, etc.
," Wang said
.
Our genome, the DNA found in each of our cells, provides a manuscript
of human evolutionary history.
The results of genetic analysis confirm some of the things we know from other sources (such as the recent rise in parental age), but also provide a richer understanding
of ancient human demographics.
These findings contribute to a better understanding of our shared history
.
”