"In places where birth control isn't practiced, women continue reproducing, and as they age they give birth to more girls," he said. "This is documented in the United States, Africa and the circum-Carribbean region." He added: "That's not to say that climate and amount of sunlight don't affect human sex ratios. But there are important things they're just not considering here." Navara admitted her finding is preliminary, and she's still searching for a solid biological mechanism to explain it. Still, she speculates that the result could be evidence of our evolutionary past; we are hard-wired to tweak the number of boys and girls we give birth to depending on cues like day length and temperature. "My sense is that this is reminding us of our evolutionary roots," she said. "We still adjust our reproductive patterns as we were originally programmed to do." Related Links: TreeHugger: Are Boys Disappearing Because of Gender Bender Chemicals? |
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