9.8: In an “alien” environment, behaviors produced by natural selection may no longer be adaptive.

The world in which alarm calling evolved did not include biologists with pickup trucks who trapped female squirrels, drove them long distances, and released them into colonies of unrelated individuals. So, when a female squirrel suddenly finds herself in this alien environment, her evolved behaviors can no longer be expected to be adaptive—no more than a human could be expected to survive on the moon. And individuals’ genes and all the behaviors they influence cannot change overnight. Adaptation to a new environment takes time, and the more quickly an environment changes, the more likely it is that the evolved behaviors of a population will no longer be appropriate.

Let’s consider another human example: donating money to refugees on another continent. To understand how natural selection could lead to this behavior, we need to understand a bit about human evolutionary history. We know from archaeological deposits that for more than two million years, our ancestors lived as hunter-gatherers in small groups of a few hundred people, at most. Their success depended on joint efforts against predators and in killing prey; being “nice” paid off when the prospect of hunting alone or sleeping outside the camp meant almost certain death. The loners died, so we are descended from those who could work well with others.

It is only recently, the blink of an eye in evolutionary time, that humans invented agriculture, industrialization, and the means of food production and distribution. As a result of these changes, most of us have easy access to unlimited amounts of food and our typical group size has increased dramatically; on a given day, you may see 10 or even 100 times as many people as a hunter-gatherer ancestor might have seen. Additionally, if you were a hunter-gatherer, all of the people in your group would be a regular part of your life. You would have many opportunities to help them and, in turn, to be helped by them. Reciprocity paid. And we evolved so that “altruistic” acts gave us pleasure, stimulating parts of our brain in ways that made us want to repeat such actions.

It is with this brain that you approach the issue of refugees halfway across the world, or a homeless family somewhere in the United States. It is likely—perhaps almost certain—that you will not have repeated interactions with any of those people. And you will probably never be in a position to be helped by them. From an evolutionary perspective, your action will almost certainly not increase your fitness. But in the world in which humans evolved, such altruistic-appearing behavior would most likely have been reciprocated at some future time—and thus your instincts guide you to, and reward you for, your kindness (FIGURE 9-14).

From the weight-control difficulties that come from easy access to food, to charitable contributions to people in faraway places, to alarm calling in transplanted squirrels, when organisms of any species find themselves in a situation where there is a mismatch between the environment they are in and the environment to which they are evolutionarily adapted, we expect (and see) behaviors that appear to be (and are) not evolutionarily adaptive. Still, understanding the process of natural selection can help us make sense of these behaviors (which in some cases can even seem nonsensical).

Can you think of other ways in which the modern industrial environment differs from the environment to which humans are adapted? How do these differences lead to situations in which our behavior, like the behavior of the transplanted Belding’s ground squirrel, may not be adaptive from an evolutionary perspective?