News | Having twins does not mean exceptionally high fertility: new research challenges the traditional image of highly fertile mothers
It has long been widely believed that women who conceive twins are naturally exceptionally fertile. However, a systematic analysis of birth records from more than 100,000 European women between 1700 and 1899 overturns this view.
The study found that having twins does not indicate unusually high fertility. In fact, mothers of twins often had lower overall fertility.
Three centuries of historical data and rigorous methods
The study used centuries of historical population data on women in preindustrial Europe. Complete birth records and limited medical intervention during this period provided an ideal sample of natural human reproductive behavior. Earlier studies often failed to distinguish between frequent ovulation and a greater number of pregnancies, making their findings easy to misinterpret.
The new study substantially improved its modeling and statistical methods and clearly separated these two factors for the first time. It found that the likelihood of twins was closely related to the number of pregnancies—cumulative opportunities for conception—rather than ovulatory function or fertility itself.
“We found that women who were more likely to have twins actually had fewer children overall,” explained study author I.J. Rickard.
Why have twins not been eliminated by natural selection?
The study also sought to explain why twinning has persisted despite its greater risks and burden.
Researchers proposed two possible evolutionary compensatory mechanisms:
Double ovulation may compensate for reproductive aging: as fertility declines with age, occasional double ovulation may physiologically compensate by increasing the chance of conception and, consequently, twins.
Where twin survival is higher, twins may increase the total number of surviving children: with relatively good medical conditions or better individual health, twins allow more children from fewer pregnancies, maintaining higher reproductive output while reducing the total number of pregnancies.
This may explain why twinning was not entirely eliminated over the course of evolution.
Twins reflect accumulated probability, not exceptional ability
From an evolutionary biology perspective, the study’s key point is that twins are not a sign of a reproductive “superpower,” but the combined result of complex physiological and statistical factors. In other words, twins more often reflect the cumulative probability of reproductive events than extraordinary individual fertility.
The study cautions the public and healthcare professionals against interpreting multiple births as evidence of high fertility. In assisted reproduction and prenatal counseling in particular, a previous twin birth should not be treated as an indicator of high future fertility.
News | Having twins does not mean exceptionally high fertility: new research challenges the traditional image of highly fertile mothers
News | Having twins does not mean exceptionally high fertility: new research challenges the traditional image of highly fertile mothers
It has long been widely believed that women who conceive twins are naturally exceptionally fertile. However, a systematic analysis of birth records from more than 100,000 European women between 1700 and 1899 overturns this view.
The study found that having twins does not indicate unusually high fertility. In fact, mothers of twins often had lower overall fertility.
Three centuries of historical data and rigorous methods
The study used centuries of historical population data on women in preindustrial Europe. Complete birth records and limited medical intervention during this period provided an ideal sample of natural human reproductive behavior. Earlier studies often failed to distinguish between frequent ovulation and a greater number of pregnancies, making their findings easy to misinterpret.
The new study substantially improved its modeling and statistical methods and clearly separated these two factors for the first time. It found that the likelihood of twins was closely related to the number of pregnancies—cumulative opportunities for conception—rather than ovulatory function or fertility itself.
“We found that women who were more likely to have twins actually had fewer children overall,” explained study author I.J. Rickard.
Why have twins not been eliminated by natural selection?
The study also sought to explain why twinning has persisted despite its greater risks and burden.
Researchers proposed two possible evolutionary compensatory mechanisms:
Double ovulation may compensate for reproductive aging: as fertility declines with age, occasional double ovulation may physiologically compensate by increasing the chance of conception and, consequently, twins.
Where twin survival is higher, twins may increase the total number of surviving children: with relatively good medical conditions or better individual health, twins allow more children from fewer pregnancies, maintaining higher reproductive output while reducing the total number of pregnancies.
This may explain why twinning was not entirely eliminated over the course of evolution.
Twins reflect accumulated probability, not exceptional ability
From an evolutionary biology perspective, the study’s key point is that twins are not a sign of a reproductive “superpower,” but the combined result of complex physiological and statistical factors. In other words, twins more often reflect the cumulative probability of reproductive events than extraordinary individual fertility.
The study cautions the public and healthcare professionals against interpreting multiple births as evidence of high fertility. In assisted reproduction and prenatal counseling in particular, a previous twin birth should not be treated as an indicator of high future fertility.
Source:
Collected online