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This is Scientific American's 60-second Science. I'm Karen Hopkin, this will just take a minute.

When it comes to lizards²' sex, size dose matter. But not in the way you might think. Because in the June 4th online issue of Journal Current Biology, scientists say that for at least one type of lizard¹, larger eggs are more likely to make girls, while smaller eggs yield boys. For many animals, the sex of an individual is dictated³ solely⁴ by its chromosomes⁵. But for small alpine⁶ lizards, gender⁷ isn’t so cut-and-dried. The scientists had earlier found that nest temperature can influence the sex of lizard hatch links. Cooler nests turn out more boys no matter what their chromosomes say. At the same time, the researchers noticed that larger eggs seemed to make more daughters. But they wanted to put their observation to the test. So they took big eggs and remove some yolk⁸ and, voila, they made males. Adding yolk to a little egg was a recipe for a female. This egg size manipulation might allow moms to balance their babies' sexes, when a chilly⁹ nest would otherwise produce mostly sons. Because when it comes to alpine lizards, sex determination all comes down to a practical yolk.

Thanks for the minute for Scientific American's 60-second Science. I'm Karen Hopkin.