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Ask Dr. Universe evolution
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Why do marine mammals have horizontal tails, but fish have vertical tails? – Peyton, 11, Washington

Dear Peyton,

When you think about a whale, you probably picture an enormous sea creature without legs. But what if I told you the first whale had four legs and could walk on land?

I talked about whales and other marine mammals with my friend Kevin Turner. He teaches marine biology at Washington State University.

He told me marine mammals have horizontal tails because they flex their bodies up and down to move. Fish flex their bodies side to side. Scientists think it has to do with the way different animals evolved.

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Why do all insects have six legs? – Charlie, 10, Ohio

Dear Charlie,

There are about 40 kinds of cats out there—like me. There’s only one kind of human on Earth now. But there are more than a million kinds of insects. That’s just the insect species we know about.

Every single one of those insects has six legs.

I talked about why that is with my friend Allan Felsot. He’s an insect scientist at Washington State University.

He told me there must be some evolutionary reason insects have six legs—like better stability when walking.

“In biology, every ‘why’ question has the same answer,” Felsot said. “Things are the way they are because of adaptations that have allowed organisms to live longer.”

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How does evolution work? – Aubree, 10, Kentucky

Dear Aubree,

When I thought about evolution, I always pictured big changes that happened over long time periods—like how birds evolved from dinosaurs.

But then I talked with my friend Jeremiah Busch. He’s a biologist at Washington State University. He told me evolution is happening all the time.

“As soon as you see that evolution is occurring around us, it changes the way you think about the world,” Busch said.

There are a few ways evolution happens. These include mutation, gene flow, genetic drift and natural selection.

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If an animal has poison inside them, how are they not affected by their own poison? – Jad, 10, Georgia

Dear Jad,

From jellyfish to snakes to spiders, lots of animals use poison or venom. It helps them catch prey and defend themselves. Even the platypus and one very spicy primate called the slow loris use venom.

I talked about your question with my friend Blair Perry. He’s a biologist at Washington State University. He’s also a snake expert.

Perry told me the difference between poison and venom. They’re both toxic mixes of mostly proteins. But they get into your body in different ways. Poison is eaten, breathed in or absorbed through the skin. Venom is injected through a bite or sting.

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