The ethologists demonstrated the genetic basis for fixed action patterns by interbreeding closely related species. Konrad Lorenz studied the courtship behaviors of different species of dabbling ducks. Some of these species, such as mallards, teals, pintails, and gadwalls, are closely related and can interbreed, but they rarely do so in nature. Each male duck performs a courtship display consisting of a precise series of movements that is typical of his species. A female is not likely to accept him unless the entire display is successfully and correctly completed.
Lorenz crossbred these duck species and found that the hybrid offspring expressed some elements of each parent’s courtship display, but in novel combinations. Furthermore, Lorenz observed that hybrids sometimes exhibited display elements that were not in the repertoire of either parent species but were seen in other dabbling duck species. Lorenz’s interbreeding studies demonstrated that the stereotypic motor patterns of the courtship displays are inherited. The observation that females were not interested in males performing hybrid displays was evidence that sexual selection had shaped these genetically determined behaviors to be *reproductive isolating mechanisms.
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*connect the concepts The evolution of populations into different species occurs when hybrids of the two populations have lower fitness. In those cases, selection favors mechanisms that prevent hybridization, and behavioral reproductive isolating mechanisms are the most common, as described in Key Concept 23.4.
The ethologists laid the foundation for the application of modern biological methods to the study of animal behavior. Tinbergen outlined the challenges for investigators as four questions:
Causation: What is the mechanism underlying the behavior, and how can the relationship between mechanisms and behavior be modified by learning?
Development: What experiences are necessary for a behavior to be displayed, and how does the behavior change with age?
Function: How does the behavior affect the animal’s chances for survival and reproduction?
Evolution: How does the behavior compare with similar behaviors in related species, and how might it have evolved?
The first two questions refer to the proximate causes of behavior: the immediate genetic, physiological, neurological, and developmental mechanisms that determine how an individual is behaving at a particular time. The third and fourth questions refer to the ultimate causes of behavior: the evolutionary processes that produced the animal’s capacity and tendency to behave in particular ways. In the sections that follow, we will describe many experiments on animal behavior. For each one, ask yourself which of Tinbergen’s four questions it addresses and whether it focuses on proximate or ultimate causes of behavior.