that result are often strategic, dependent upon changes in climate, other competitors, who happens to be in a bad mood, and who is sexually active. In a variety of species, from dung beetles to deer, biologists have developed mathematical models that accurately predict how long an individual should wait for a sexual partner or feed in a food patch. The accuracy of these models shows that individuals’ desires for resources linked to survival and reproduction are captured by lawful principles or rules. This is important because it means we understand how the machine underlying behavior works. It means we understand how animals make certain choices.
Understanding how wanting works is straightforward. In both humans and nonhuman animals, we can measure what individuals approach when we give them a choice, as well as how much effort they are willing to exert while approaching and gaining access to a particular object or experience. For example, in studies that explore whether captive animals are provided with sufficient housing conditions, an experimenter presents individuals with a choice of rooms, one consisting of the typical housing environment and the others by the addition of goods believed to be of interest. To enter a given room requires opening a door. To determine how much an individual really wants what is in another room, the experimenter ramped up the difficulty of opening each door. In studies of captive hens and mongoose, individuals exerted considerable effort to open some doors but not others. Hens rammed into doors opening onto a chipped wood floor, whereas mongoose did the same for a pool of water. These are items they want, but do not get in captivity.
What about liking? It may seem, at first blush, that because liking is a subjective experience, that there are no clear objective ways to measure it. My likes are my own. You can’t possibly know what it is like to be me. If you can’t know what it is like to be me, then we can’t possibly know what it is like to be a mongoose, mouse or monkey. There are, however, ways of measuring liking and disliking that are reliable, objective, and consistent across species. In many animals, including human babies who can’t speak and human adults who have lost this capacity due to brain injury, there are distinctive behaviors that are consistently linked to positive experiences and others linked to negative ones. For example, in mice, monkeys, and human babies, tasting something sweet like sugar causes a lot of lip licking, whereas tasting something bitter such as quinine causes mouth gaping, nose twitching, and arm flailing. These similarities show that evolution has been conservative, maintaining the same underlying mechanisms for handling likes and dislikes. These similarities have enabled scientists to understand how the brain systems involved in wanting and liking can change together or separately, even though they can’t help us understand the harder problem of what, in particular, it is like for a given mouse, monkey or man to like something.
To understand the machinery that drives rodent wants or desire, Susana Pecifia and Kent Berridge
took advantage of the genetic technique that Joe Tsien —mentioned in the last chapter — used to create
Hauser Chapter 2. Runaway desire 59
HOUSE_OVERSIGHT_012805