Is there evidence that optimistic women are more likely to have sons? Researchers previously observed that healthy, carefree women who consumed substantial food quantities often gave birth to sons, while impoverished women typically bore daughters.
This latest study, published in Biology Letters, surveyed 609 mothers in Gloucestershire. One question asked, "How long do you expect to live?"
Women from lower-middle-class backgrounds and working-class families estimated their lifespans at 40 years, while others believed they could live to 130.
Dr. Johns suggests the link between projected longevity and the sex of a woman's first child may stem from a "selfish" behavior of human genes.
Evolutionary biologists call this the Trivers-Willard hypothesis. It suggests that when a mother faces stressors—such as poor health, harsh living conditions, or food scarcity—biological cues may lead her to conceive a girl rather than a boy.
However, this recent finding does not imply women can alter their first child's gender by changing their outlook on the future.
Dr. Johns stated that the findings do indicate a link between infant sex and maternal personality. "You can observe this in modern populations, which is quite astonishing."
Evolutionary psychologist Robin from the University of Liverpool noted that while the research is intriguing, biologists still don't fully understand why this phenomenon occurs.