If you're enjoying this podcast, we would love to tell you about Common Descent.

Common Descent is a podcast about paleontology, evolution, and the history of life on Earth,

hosted by two paleontologists with an unending enthusiasm for the wonders of the world.

Each episode cover science news, followed by a deep dive into a main topic requested by the audience.

Recent episodes of feature topics like eels, hibernation, and fungi.

In addition to the main series, Common Descent also features side projects that explore science and pop culture,

where the host examined the science and movies or speculate on the hypothetical evolution of fictional monsters.

Listen to Common Descent on Spotify, Apple, or wherever you get your podcasts.

It's a warm Friday evening in September of 2013.

Standing in this field of tall golden grass swaying gently in the breeze, you'd have no

idea that one of the largest cities in the world, Johannesburg, South

Africa, is less than a 30-minute drive away. You also wouldn't know that 30 meters below you

lies a vast stone labyrinth of sharp twists and narrow passageways formed millions of years ago.

Unless you were a caver.

This cave system, known as Rising Star Cave, has been known to caver since the 1960s.

And since then, many sections of the dark winding expanse have been mapped.

But with an intricate underground system like this, there's often more to find.

As you enter the cave, dropping vertically down into the earth, you see the last of the day's

light as a small circle of sky.

The initial downward slope is steep as the cave descends. Stalactites glitter in the lights

of your headlamp. Suddenly, the passage narrows, leaving just a small gap between the

ceiling and the floor. It'll be a tight squeeze. Flat on your stomach, you peer through the gap and see

...