The study looked at 461 parents of psychology students at Singidunum University in Belgrade, Serbia.
The research, published in Journal of Biosocial Science, revealed the more religious the parents were, the more children they wanted to have, and the more they ended up having.
Dr Janko Mededovic, the scientist who led the study, said he wanted to add to 15 years of past research in finding the link to the "evolution of religiousness".
It's thought that religion is continuing in society because it's being passed down from generations of families.
Dr Mededovic said: "If individuals with higher religiosity have elevated reproductive success, then natural selection could actively propagate [genetic variations] that contribute to the expression of religious affiliation.
"In this case it could be reasonably assumed that religiousness does have an adaptive function in contemporary humans."
The study's findings echo statistics from the 2016 census of almost 4 million women in 32 countries, which revealed those who had a religious belief were less likely to not have any children.
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