Flynn's research collated IQ examination results from New Zealand, Australia, the United States, Canada, Argentina, Estonia and countries in western Europe.
In New Zealand, Estonia and Argentina, women scored marginally more than men.
However, in Australia the results were almost identical for both sexes.
One possible explanation is that women's lives have become more demanding as they multitask between raising a family and doing a job, Flynn said.
Another is that women have a slightly higher potential intelligence than men and are only now realising it.
Mr Flynn, who will publish his findings in a book, said more data was needed to explain the trend.
"The full effect of modernity on women is only just emerging," he added.
The data for making exact comparisons between countries was sparse.
Mr Flynn said: "As the world gets more complex, and living in it demands more abstract thought, so people are adapting."
He added: "I suspect that the same trends are happening in Britain, too, although the data is too sparse to be sure."