Biology
The Evolution of Viviparity in Squamate Reptiles and Its Physiological Constraints
Quick fact
Squamate reptiles have evolved viviparity independently more than 100 times—far more than any other vertebrate group—often in response to cold or unpredictable environments.
Why this is interesting
Most reptiles lay eggs, yet some snakes and lizards give birth to live young. How could this dramatic shift evolve—and what does it cost the mother?