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College of Arts and Sciences Erica Crespi

Dr. Universe: Why are animals symmetrical?

Dr. Universe: a cat in a lab coatIf we drew an imaginary line straight down the middle of the human body, it would look pretty similar on each side.

We see this kind of symmetry in lots of animals, from cats and birds to worms and frogs. In fact, about 99 percent of animals have bilateral or two-sided symmetry, says my friend Erica Crespi, a biologist at Washington State University who studies frogs and asks a lot of big questions about how animals develop.

Imagine if animals like frogs, birds, cats, or humans didn’t have their two-sided symmetry. Birds might have a hard time flying with one wing. Frogs might hop in circles » More …