The study, which is discussed in his book ‘The Intelligence Paradox,’ cites data from UK’s National Child Development Study with added economic and education information.
According to Kanazawa, “if any value is truly unnatural, if there is one thing that humans (and all other species in nature) are decisively not designed for, it is voluntary childlessness,” the New York Daily News reported
In the book, he goes on to say in a chapter called “Why Intelligent People Are the Ultimate Losers in Life” that all living organisms are “evolutionarily designed to reproduce” and that “reproductive success is the ultimate end of all biological existence.”
According to the Guardian, Kanazawa doesn’t give a reason why this is a case, and it’s not clear why some of these “loser” women elect to do something as “unnatural” as not having children.
However, it is becoming more common, at least in the United States. According to a Pew Research report from 2010, one in five American women did not have children when her biological clock stopped ticking, compared to one in 10 in the 1970s.