How Ultrasound Changed the Human Sex Ratio

Editor’s Note: The following is an excerpt from Mara Hvistendahl’s book , Unnatural Selection: Choosing Boys over Girls and the Consequences of a World Full of Men. The technology that ultimately became the dominant method of sex selection around the world began as a tool for navigation. The story of ultrasound dates to 1794, when an Italian biologist curious about how bats find their way in the dark discovered sonar, or the fact that distance can be determined by bouncing sound waves off a faraway object and measuring how long it takes for the waves to ricochet back

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How Ultrasound Changed the Human Sex Ratio