This is the 2007 version. Click here for the 2017 chapter 08 table of contents.

The Impact of Environmental Change

The adaptive value of a behavior, or any other trait, is always relative to some environment. When the environment changes, so does the adaptive value of a particular behavior.

How is the twig-using behavior of Galapagos Islands finches an adaptation?

On the famous Galapagos Islands where Darwin made many of his observations, the Woodpecker Finch uses twigs and cactus spines to probe for insects in holes of dead trees. This is an excellent example of an adaptive behavior in a particular environment. It represents an adjustment to the environment of the islands, where insects in the trees provide food for the finches, which gives the finches an evolutionary advantage. By exploiting this food source, they are more likely to survive and reproduce than finches that cannot use twigs in this way.

Why might woodpeckers invading the Galapagos Islands make certain finches extinct?

However, the finch's behavior is adaptive only because there are no woodpeckers on the island. If there were woodpeckers in the area, the finch's behavior would no longer give it a reproductive advantage. Woodpeckers are more efficient at extracting insects from dead wood, so food would not be available for the twig-using finch, and it might become extinct.

To interpret the fitness or adaptive value of a behavior, one must specify the environment. That includes the other creatures present. The introduction or extinction of a single new species can tip the balance of survival for dozens of other species in that ecosystem. For exapmle, cats introduced to island ecosystems by humans have a devastating effect. They are excellent predators and the animals living on isolated islands have no evolved defenses against them. Fire ants have devastated competing ant species in the southern U.S. In Europe, the arrival of modern humans around 40,000 years ago probably caused the extinction of the Neanderthals, who had lived there for 300,000 years. Again and again, the fossil record shows that the arrival of modern humans in an ecosystem is followed by the mass extinction of large animals in the same area, probably due to hunting. Early humans are now believed to have hunted the wooly mammoth to extinction.

What are examples of humans modifying their own environments, to their own detriment?

Humans are often so successful at modifying their environments that they bring about the destruction of their own societies. The Maya civilization burned wood to cook limestone, which was ground up and used to make a form of concrete, the main construction material for their massive ceremonial temples. Simple calculations show that this consumption of forest resources was unsustainable. Eventually all the trees were gone, and that (along with a drought and a belief system predicting the end of the world) led to the end of Mayan civilization.

A similar process occurred on Easter Island, where an isolated population of humans cut down the native species of trees until they were all gone. The ecosystem was devastated and the humans eventually faced repeated famines. Many similar events are occurring today, for example, in fishing villages of the northeastern United States, where a traditional way of life is dying because the level of fishing has reduced stocks to the point where people can no longer make a living by fishing.

How can evolutionary psychology help us solve modern problems?

On issue after issue—including some of the most significant problems of modern times—the challenge facing our species is to modify our behavior intelligently so we can encourage cultural and behavioral practices that are healthy and sustainable, while discontinuing those that are self-defeating. Evolutionary psychology may help. In some cases, simulations may suggest adaptive strategies for the future. In many other cases, evolutionary psychology can help by explaining the origins of destructive behavior patterns left over from the past. If we understand where they came from and how they might have been adaptive in ancient times, it may help us to move beyond them and not to continue blindly with practices that are maladaptive in the modern world.

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Copyright © 2007-2011 Russ Dewey