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Evolution And Paths Cut Short

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The Nautilus (pictured above) is considered a living fossil, meaning it hasn't changed much since it first appeared 500 million years ago.
Mehgan Murphy, Smithsonian's National Zoo
The Nautilus (pictured above) is considered a living fossil, meaning it hasn't changed much since it first appeared 500 million years ago.

In a darkened tank at the National Zoo, some very odd creatures are clinging to the rocky walls. They're called nautilus, and they look like a cross between a squid and a snail.

"I'm standing in front of a nautilus tank -these are chambered nautilus, explains Alan Peters, curator of invertebrates for the National Zoo. "They're quite incredible animals."

Nautilus have been noted as a living fossil - a currently living animal with a similar body shape and form to what it was a long time ago. In the case of nautilus, it's over 500 million years ago, and this is the last of those members that exists today, says Peters.

Half a billion years and it's still around. And, it's a small, leafy green branch on a massive hulking family tree that's mostly... dead.

"Many people are familiar with ammonites that have some similarity in the shape," says Peters. "There were an incredible number - its beautiful to look at an array of all the different designs, just hundreds of thousands of different shapes and designs, some of them very similar, slight changes, some of them quite dramatic. They came around 400 million years ago, and they were extinct at about 65 million years, so they came and went."

The struggle to survive

Living fossils are unique not just because they haven't changed a lot, but also because they've survived at all.

"When we look at species we have today, estimates range up into the millions, and we don't know how many there are," says Alex Pyron, professor of biology at George Washington University. "But what we do know is 99.9 percent of all species that have ever existed have gone extinct. So that could be as many as 50 billion species."

When you look at a modern family tree, it looks as if things are branching off. But pruning - extinction - is right there behind it, constantly nipping at its heels.

"It's called the Red Queen hypothesis, says Pyron. "It's the idea coming from Through The Looking Glass the Alice and Wonderland book that you have to run as fast as you can just to stay in one place, and anything that trips you up will, 'cause you fall behind. So at any given time, every single species is in a constant race for survival, and a constant struggle to get by just to reproduce to the next generation. And you have a constant, completely random set of mutations that arise that might give them beneficial adaptations. But the same thing is happening in all of the other creatures in the environment, and the environment is changing too."

So maybe the temperature changes, or a new creature with a snazzy new adaptation comes in, and pushes you and your whole branch on the family tree of life aside. Pyron says all of a sudden, they fall behind in the struggle. "And they get trampled underfoot, so some other group is king of the hill."

Pyron says this happened with snakes. About 60 million years ago, some lucky snakes evolved venom through small modifications to proteins in saliva. Sixty million years later, they've blown other snake groups out of the water in terms of diversity. So if survival is all about change, how have living fossils, such as the nautilus at the National Zoo, hung on for so long?

The secret to survival

Christopher Wilkins, author of the book Darwinian Tourist, says living fossils are usually adapted to a particular ecological niche.

"Ecological niches, of course, come and go, and some ecological niches are very brief," says Wilkins. "There are some parts of the world that really haven't changed very much for different periods of time, and that has allowed certain species to persist. Their ecological niche is one they've become well adapted to; they're able to repel other organisms that want to take the niche over."

But that makes them vulnerable too. If that niche changes, like it has for just about everything else in the world, they could become extinct.

"The organisms that are best able to survive big changes are going to be the generalist organisms that can utilize a variety of different ecological niches," says Wilkins.

Think roaches or rats. But if everything else is destined to fade away or evolve into something else, what about us?

"Humans are a different case though, I hate to stick my neck on this," Wilkins says. "Everyone assumes we're going to blow ourselves up, or flood the whole planet. I think that first of all, we'll be smart enough to avoid those fates. Second, that our species is clever enough to be able to adapt to changing environments, and we are of course able to create our own environment, so maybe the rules have changed a little bit."

So maybe we'll work things out too, just like the venomous snakes and the roaches.

Music: "Not Fade Away (In the Style of The Rolling Stones)" by Zoom Karaoke from Zoom Karaoke - The Rolling Stones 2) / "Don't Look Back In Anger (Instrumental Version)" by Easy Karaoke Players from Easy Instrumental Hits, Vol. 102 (Karaoke Version)

Photos: Evolution And Paths Cut Short


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