Evolution in Action

Lizard Lays Egg and Births Babies

Photo: Rebecca A. Pyles

Scientists studying a species of Australian lizard called the yellow-bellied three-toed skink discovered that they’re seeing evolution in action: the lizard lays eggs on coasts but birth babies in mountains.

Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.
But modern reptiles that have live young provide only a single snapshot on a long evolutionary time line, said study co-author James Stewart, a biologist at East Tennessee State University. The dual behavior of the yellow-bellied three-toed skink therefore offers scientists a rare opportunity.
"By studying differences among populations that are in different stages of this process, you can begin to put together what looks like the transition from one [birth style] to the other."

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