TED日本語 - ローレン・サラン: 進化で勝ち残り、大絶滅を生き延びる方法

Congratulations. By being here, listening, alive, a member of a growing species, you are one of history's greatest winners -- the culmination of a success story four billion years in the making. You are life's one percent. The losers, the 99 percent of species who have ever lived, are dead -- killed by fire, flood, asteroids, predation, starvation, ice, heat and the cold math of natural selection. Your ancestors, back to the earliest fishes, overcame all these challenges. You are here because of golden opportunities made possible by mass extinction.

(Laughter)

It's true. The same is true of your co-winners and relatives. The 34,000 kinds of fishes. How did we all get so lucky? Will we continue to win? I am a fish paleobiologist who uses big data -- the fossil record -- to study how some species win and others lose. The living can't tell us; they know nothing but winning. So, we must speak with the dead.

How do we make dead fishes talk? Museums contain multitudes of beautiful fish fossils, but their real beauty emerges when combined with the larger number of ugly, broken fossils, and reduced to ones and zeros. I can trawl a 500-million-year database for evolutionary patterns. For example, fish forms can be captured by coordinates and transformed to reveal major pathways of change and trends through time.

Here is the story of the winners and losers of just one pivotal event I discovered using fossil data. Let's travel back 360 million years -- six times as long ago as the last dinosaur -- to the Devonian period; a strange world. Armored predators with razor-edge jaws dominated alongside huge fishes with arm bones in their fins. Crab-like fishes scuttled across the sea floor. The few ray-fin relatives of salmon and tuna cowered at the bottom of the food chain. The few early sharks lived offshore in fear. Your few four-legged ancestors, the tetrapods, struggled in tropical river plains. Ecosystems were crowded. There was no escape, no opportunity in sight. Then the world ended.

(Laughter)

No, it is a good thing. 96 percent of all fish species died during the Hangenberg event,359 million years ago: an interval of fire and ice. A crowded world was disrupted and swept away.

Now, you might think that's the end of the story. The mighty fell, the meek inherited the earth, and here we are. But winning is not that simple. The handful of survivors came from many groups -- all greatly outnumbered by their own dead. They ranged from top predator to bottom-feeder, big to small, marine to freshwater. The extinction was a filter. It merely leveled the playing field. What really counted was what survivors did over the next several million years in that devastated world. The former overlords should have had an advantage. They became even larger, storing energy, investing in their young, spreading across the globe, feasting on fishes, keeping what had always worked, and biding their time. Yet they merely persisted for a while, declining without innovating, becoming living fossils. They were too stuck in their ways and are now largely forgotten.

A few of the long-suffering ray-fins, sharks and four-legged tetrapods went the opposite direction. They became smaller -- living fast, dying young, eating little and reproducing rapidly. They tried new foods, different homes, strange heads and weird bodies.

(Laughter)

And they found opportunity, proliferated, and won the future for their 60,000 living species, including you. That's why they look familiar. You know their names.

Winning is not about random events or an arms race. Rather, survivors went down alternative, evolutionary pathways. Some found incredible success, while others became dead fish walking.

(Laughter)

A real scientific term.

(Laughter)

I am now investigating how these pathways to victory and defeat repeat across time. My lab has already compiled thousands upon thousands of dead fishes, but many more remain. However, it is already clear that your ancestors' survival through mass extinction, and their responses in the aftermath made you who you are today.

What does this tell us for the future? As long as a handful of species survive, life will recover. The versatile and the lucky will not just replace what was lost, but win in new forms. It just might take several million years.

Thank you.

(Applause)