Judy Woodruff: Tonight's Brief But Spectacular features ichthyologist Prosanta Chakrabarty, who studies fish to help explain the evolution of human beings and the planet.

He's a professor and curator of fishes at the Museum of Natural Science and Department of Biological Science at Louisiana State University.

Prosanta Chakrabarty: Every once in a while, you go to someplace new, where no one has been before, and you see something that is so different that you know it's new right away.

It's like, what is this thing? This is so new, I can't believe it. I'm going to go home now and describe this thing before anyone else finds out about it.

I grew up loving animals and nature, despite growing up in Queens, New York. And I went as a kid to the Bronx Zoo and the American Museum of Natural History and looked up at dinosaurs and blue whales, and I never looked down. I just wanted to study biology.

In the bigger scheme, I'm trying to understand who's related to whom on this planet.

One of the things I love to study are freshwater fishes. So, one cave fish is in Australia, and the other one is in Madagascar, which is actually a thing I discovered. Their last connection together wasn't through swimming across the Pacific Ocean, which — where they wouldn't be able to survive. Instead, they were last together when those continents were together almost 100 million years ago.

The tools that we have available to us are everything from the DNA of the organism to the bodies of the organisms. We can study entire genomes now. And so we can understand things at levels that weren't possible in the past.

The things that I have learned about geological history is just how interconnected this planet is. I have learned, you know, going to the Persian Gulf, which is only about 20,000 years old, that this area can tell me about why it rains so much in the Himalayas during monsoon season, or why the connection between North and South America, which is only three million years old, has led to climate change that's changed the dimensions of this planet and the currents.

Sometimes, what I'm doing is putting together a puzzle, but I don't have that little box that tells me what the puzzle will be. And so each little piece is a different species on the planet.

And the other problem is, many of those species that I need to fill in the puzzle have gone extinct.

My name is Prosanta Chakrabarty, and this is my Brief But Spectacular take on life on Earth.

Judy Woodruff: And you can find more episodes of our Brief But Spectacular series on our Web site,