MS. REBECCA SHEIR
So today's show is all about the road not taken and in this next story we'll hear about a bunch of roads not taken because the travelers taking those roads no longer exist. It's all about evolution, which scientists will tell is chock full of abrupt dead-ends and sudden twists and turns. Environment reporter, Sabri Ben-Achour, brings us all the Darwinian details.
MR. SABRI BEN-ACHOUR
In a dark tank at the National Zoo, some very odd creatures are clinging to the rocky walls. They look like a cross between a squid and a snail.
MR. ALLEN PETERS
These are chambered Nautilus. They're quite incredible animals.
Allen Peters is curator of invertebrates.
Well, it has a spiral shell, the tentacles are right in the front and Nautilus have been noted as a living fossil, an animal that's living now and its body shape, its body form, is very similar to its ancestors that lived very, very long time ago. In the case of Nautilus, it's over 500 million years ago.
Half a billion years and it's still around. and if you look at its family tree, the tree is massive, it's hulking. And the Nautiloids are just a small leafy green branch, but the tree is mostly dead.
Many people familiar with amenities that have some similarity in the shape, there were an incredible number. I mean, it's beautiful to just look at an array of all the different designs. There are just hundreds and thousands of different shapes that came and went.
Living fossils are unique, not just because they haven't changed a lot but also because they've survived at all. Alex Pyron is a professor of biology at George Washington University.
PROF. ALEX PYRON
When we look at the species we have today, we have, the estimates range up into the millions and we don't really know how many there are, but what we do know is that 99.9 percent of all species that have ever existed have gone extinct. So that could as many as 50 billion species.
When you look at a modern family tree it looks as if things are branching, branching. But pruning, extinction, is right there behind it, constantly nipping, nipping, nipping at its heels.
It's called the Red Queen Hypothesis. It's the idea coming through the looking glass, the "Alice in Wonderland" book that you have to run as fast as you can just to stay in one place and that anything that trips you up will cause you to fall behind. So at any given time every single species is in a constant race for survival and a constant struggle just 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.
All of a sudden, basically, they fall behind the struggle and they get trampled underfoot. So some other group is now king of the hill.
Pyron says this happened with snakes. About 60 million years ago some lucky snake evolved venom through small modifications to proteins and saliva. 60 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 or horseshoe crabs or coelacanths, how have they hung on for so long? Christopher Wills is a biologist and author of the book "The Darwinian Tourist."
MR. CHRISTOPHER WILLS
Living fossils usually are beautifully adapted to a particular ecological niche. Ecological niches of course come and go but there are some parts of the world that really haven't changed very much over long periods of time. And that has allowed certain species to be able to persist.
But that makes them vulnerable, too. If that niche changes like it has for just about everything else in the world, they could be goners.
The organisms that are best able to survive these big changes are going to be the generalist organisms that can utilize a variety of different ecological niches.
Think roaches or rats. But if everything else is destined to fade away or evolve into something else, what about us?
Humans are a sort of a different case, though. I kind of hate to stick my neck out on this because everyone assumes that we're going to blow ourselves up or flood the entire planet or something. I think that first of all, hopefully we'll be smart enough to be able to avoid those fates. Second, that our species is clever enough to be able to adapt and we are, of course, able to create our own environment, to a large extent. So maybe the rules have changed a little bit here.
So maybe we'll work things out, too, just like the venomous snakes and the roaches. I'm Sabri Ben-Achour.
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