Mothers and daughters often share the same birth month – and scientists now know why.
New research shows that women are more likely to have children in the same month as their own birth than scientists expected.
The study also found that siblings tend to share month of birth with each other, as do children and fathers, and parents are born in the same month as one another more often than would be predicted.
To get their results the team, from The City University of New York, analyzed data from more than 10 million births.
The findings, published in Population Studies, showed that there were 4.6% more births in which mother and child shared the same birth month than would be expected.
So, there was a spike in January births among the mothers who were born in January, a spike in February babies in the mothers who were born in February and so on.
The phenomenon likely has its roots in relatives sharing socio-demographic characteristics: people of similar backgrounds are known to pair up and to be more likely to give birth at certain times of the year.
The researchers explained that in Spain, for example, a woman with a higher education is more likely to give birth in the spring than woman without a higher education.
If she has a daughter, in addition to being more likely to be born in the spring, this daughter may be more likely to have higher education, since her mother has it.
And thus, when this daughter has children, she will be more likely to have them in the spring too.
As a result of this, the season and even month of birth can be passed down through generations.
Dr. Adela Recio Alcaide said: “What could cause the higher probabilities of family members being born in the same season? The potential explanations seem to be both social and biological.
“The excess of children with a father and mother born in the same month seems to be due to social or behavioral causes prior to conception that relate to the choice of a partner born in the same month, as we have observed this excess with marriage statistics, with spouses being more likely to mate with someone from the same month.”
Professor Luisa Borrell added: “This may not be surprising considering things such as partnerships tend to be formed by people with similar socio-demographic characteristics.
“Moreover, biological factors that are known to affect birth seasonality—such as photoperiod exposure, temperature, humidity, and availability of food—also depend on socio-demographic characteristics, since different social groups are exposed to these biological factors to varying degrees.”
Produced in association with SWNS Talker
