"But why would group behavior change?" Thorne said. "If there wasn't some external catastrophe to force it, why should the behaviour change?"
"Actually," Malcolm said, "behavior is always changing, all the time. Our planet is a dynamic, active environment. Weather is changing. The land is changing. Continents drift. Oceans rise and fall. Mountains thrust up and erode away. All the organisms on the planet are constantly adapting to those changes. The best organisms are the ones that can adapt most rapidly. That's why it's hard to see how a catastrophe that produces a large change could cause extinction, since so much change is occurring all the time, anyway."
"In that case," Thorne said, "what causes extinction?"
"Certainly not rapid change alone," Malcolm said. "The facts tell us that clearly."
"What facts?"
"After every major environmental change, a wave of extinctions as usually followed-but not right away. Extinctions only occur thousands, or millions of years later. Take the last glaciation in North America. The glaciers descended, the climate changed severely, but animals didn't die. Only after the glaciers receded, when you'd think things would go back to normal, did lots of species become extinct. That's when giraffes and tigers and mammoths vanished on this continent. And that's the usual pattern. It's almost as if species are weakened by the major change, but die off later. It's a well-recognized phenomenon."
"It's called Softening Up the Beachhead," Levine said. "And what's the explanation for it?"
Levine was silent.
"There is none" Malcolm said. "It's a paleontological mystery. But I believe that complexity theory has a lot to tell us about it. Because if the notion of life at the edge of chaos is true, then major change pushes animals closer to the edge. It destabilizes all sorts of behavior. And when the environment goes back to normal, it's not really a return to normal. In evolutionary terms, it's another big change, and it's just too much to keep up with. I believe that new behavior in populations can emerge in unexpected ways, and I think I know why the dinosaurs - "
"What's that?" Thorne said.
Thorne was looking at the trees, and saw a single dinosaur hop out into view. It was rather slender, agile on its hind legs, balancing with a stiff tail. It was six feet tall, green-brown with dark-red stripes, like a tiger.
"That," Malcolm said, "is a velociraptor."
Thorne turned to Levine. "That's what chased you up in the tree? It looks ugly."
"Efficient," Levine said. "Those animals are brilliantly constructed killing machines. Arguably the most efficient predators in the history of the planet. The one that just stepped out will be the alpha animal. It leads the pack."
Thorne saw other movement beneath the trees. "There's more."
"Oh yes," Levine said. "This particular pack is very large." He picked up binoculars, and peered through them. "I'd like to locate their nest, he said. "I haven't been able to find it anywhere on the island. Of course they're secretive, but even so..."
The parasaurs were all crying loudly, moving closer to the apatosaur herd as they did so. But the big apatosaurs seemed relatively indifferent; the adults nearest the water actually turned their backs to the approaching raptor.
"Don't they care?" Arby said. "They're not even looking at him,"
"Don't be fooled," Levine said, "the apatosaurs care very much. They may look like gigantic cows, but they're nothing of the sort. Those whiptails are thirty or forty feet long, and weigh several tons. Notice how fast they can swing them. One smack from those tails would snap an attacker's back."
"So turning away is part of their defense?"
"Unquestionably, yes. And you can see now how the long necks balance their tails."
The tails of the adults were so long, they reached entirely across the river, to the other shore. As they swung back and forth, and the parasaurs cried out, the lead raptor turned away. Moments later, the entire pack began to slink off, following the edge of the trees, heading up into the hills.
"Looks like you're right," Thorne said. "The tails scared them off."
"How many do you count?" Levine said.
"I don't know. Ten. No, wait - fourteen. Maybe more. I might have missed a few."
"Fourteen." Malcolm scribbled in his notebook.
"You want to follow them?" Levine said.
"Not now."
"We could take the Explorer."
"Maybe later," Malcolm said.
"I think we need to know where their nest is," Levine said. "It's essential, Ian, if we're going to settle predator-prey relationships. Nothing is more important than that. And this is a perfect opportunity to follow - "
"Maybe later," Malcolm said. He checked his watch again.
"That's the hundredth time you've checked your watch today," Thorne said.
Malcolm shrugged. "Getting to be lunchtime," he said. "By the way, what about Sarah? Shouldn't she be arriving soon?"
"Yes. I imagine she'll show up any time now," Thorne said.
Malcolm wiped his forehead. "It's hot up here."
"Yes, it's hot."
They listened to the buzzing of insects in the midday sun, and watched the raptors retreat.
"You know, I'm thinking," Malcolm said. "Maybe we ought to go back."
"Go back?" Levine said. "Now? What about our observations? What about the other cameras we want to place and - "
"I don't know, maybe it'd be good to take a break."