Can Police Dogs Identify Criminal Suspects by Smell

Using Experiments to Test Hypotheses about Animal Behavior

We know from our everyday experience with pets that animals have different sensory abilities than humans. In many cases, it's obvious that these sensory abilities far exceed our own. Even the most casual observers, for example, would soon realize that their dogs live in a world dominated by odors and that they can detect and dist inguish odors unk nown to the owners. Indeed, some of the most fascinating stories in biology involve the discovery of specialized sensory abilities in particular types of animals that are totally lacking in humans. A classic example is Donald Griffin's (1986) discovery of echolocation by bats. Many bat s emit streams of high-frequency sounds, well above the highest frequency that we can hear. These sounds bounce off object s in the environment, and the bat s use the result ing pattern of echoes to navigate under pitch-black conditions at night. They also use echolocat ion to locate their prey, such as moths and other flying insects. This is an exquisite adaptation for success for a highly mobile, noct urnal, aerial predator of small prey that are also highly mobile.

The excitement of Griffin's discovery arises from the fact that, as humans, our primary tools for learn ing about the world are our own sensory abilities of taste, touch, smell, and especially hearing and vision. This has always been the case and is st ill largely true, despite the complex machinery for collect ing and analyzing data that we associate with modern science (after all, the output of the machines generally has to be looked at or listened to by people in order to be interpreted). Because we depend on our limited sensor y abilities for doing science, learning about sensory abilities of other animals that differ qualitatively or quantitatively from our own is part icularly challenging. In the case of echolocation, European scientists discovered in the late 1700s that blinded bats could navigate in a room but bats whose ears were plugged with wax could not. Griffin repeated these experiments in the 1940s but was able to use new acoustic equipment to record the high-frequency sounds of the bats, finally solving the mystery of how bats navigate that had intrigued the European researchers 150 years earlier.

Donald Griffin (1986) describes his discovery of echolocation in a wonderful book for a general audience called Listening in the Dark. It's a tale of imagination, invention, and the design and execution of critical experiments. I'll use an example that is somewhat less exotic but especially well suited to illustrating the experimental method. It is the opposite of the echolocation story because it is about the limits of the olfactory abilities of dogs, which are often assumed to be virtually unlimited . Rather than inspiring our awe that animals can do something that we never imagined would be possible, such as navigate by echolocation, this story about the sense of smell in dogs shows how common k nowledge can somet imes get ahead of scient ific evidence, with significant pract ical consequences. In debunk ing the health benefit s of v itamin C in Chapter 2 and the olfactory abilities of dogs in this chapter, I don't want to leave you with the impression that experiment s are always used to discredit popular hypotheses. The next chapter will illustrate the positive role of experiments combined with other kinds of evidence to evaluate hypotheses.

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