Using the language of evolution, success in the survival game equates to “fitness.” The fittest survive and procreate. Obviously some individuals score better in this game than others. Biologists like to describe such differences in fitness in geographic terms, using the metaphor of a landscape. Using this metaphor, you can think of fitness—or the goal of a game—as getting a good vantage point, living on the peak of a mountain with a good view of your surroundings. For convenience you can describe your fitness just by specifying your latitude and longitude on the landscape map. Some latitude–longitude positions will put you on high ground; some will leave you in a chasm. In other words, some positions are more fit than others. It’s just another way of saying that some combinations of features and behaviors improve your chance to survive and reproduce. Real biological fitness is analogous to the better vantage point of a mountain peak.

In a fitness landscape (just like a real landscape) there can, of course, be more than one peak—more than one combination of properties with a high likelihood for having viable offspring. (In the simple landscape of the all-bird island, you’d have a dove peak and a hawk peak.) In a landscape with many fitness peaks, some would be “higher” than others (meaning your odds of reproducing are more favorable), but still many peaks would be good enough for a species to survive.

On a real landscape, your vantage point can be disturbed by many kinds of events. A natural disaster—a hurricane like Katrina, say, or an earthquake and tsunami—can literally reshape the landscape, and a latitude and longitude that previously gave you a great view may now be a muddy rut. Similarly in evolution, a change in the fitness landscape can leave a once successful species in a survival valley. Something like this seems to be what happened to the dinosaurs.

You don’t need an asteroid impact to change the biological fitness landscape, though. Simply suppose that some new species moves into the neighborhood. What used to be a good strategy— say, swimming in the lake, away from waterphobic predators— might not be so smart if crocodiles move in. So as evolution

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