Throughout his life Ernst Mayr was interested in the behavior of animals beginning with his intimate observations of bird behavior during his youth (p. 24). In later years he published occasionally brief notes on his behavioral observations of certain bird species (1941l, 1948f,g) and was particularly interested in behavioral isolating mechanisms between closely related species. An outcome of this interest were his experimental studies on the behavior of two species of Drosophila flies (p. 228). Also about half of his graduate students chose behavioral topics for their thesis work (9 of 16 PhD students, p. 262). During the 1960s and 1970s, Mayr repeatedly discussed the relations between behavior and evolution in his text books (1963b, 1970e) and in a series of articles (1958g, 1971c, 1974j, 1976c, 1977c). While behavioral characters are quite important at the species level, Mayr found that relatively few higher taxa possess diagnostic behavioral features. The first paper mentioned above (1958g) also lists cases where analogous behaviors were acquired by unrelated groups and others where a study of behavior led to an improvement of classification. This paper shows also that behavior is often the pacemaker in evolution, a behavior pattern appearing prior to the origin of more specialized, facilitating structures. In 1974(j) Mayr discussed his concept of closed and open behavioral programs in more detail than previously as well as their respective roles in evolution. Most organisms have a fixed (closed) program for certain "purely instinctive" activities. Other behaviors are steered by previous experience (open programs), particularly in species which have a long period of parental care, when sufficient time for learning exists in the offspring. However, an open program is by no means a tabula rasa and certain types of information are more easily incorporated than others. Mayr concluded that display activities which are in part permitting the recognition of conspecific individuals must be based on closed programs. There is no opportunity for learning, and any errors in such behavior are usually strongly selected against. On the other hand, non-communicated behavior deals largely with the exploration of the environment, and flexibility of this type of behavior (open programs) should be of selective advantage. Later suggestions that sexual selection may play an important role in the evolutionary change of behavioral isolating mechanisms indicated that some programs for courtship behavior and pair formation are less closed than Mayr had expected such as those of, e.g., the strikingly different geographical representatives of several groups of birds of paradise (Parotia, Astrapia, Fig. 4.15). Since these are relatively recent species the change probably occurred rather rapidly without having been greatly impeded by any selection for maintenance of the ancestral species recognition marks. P. Ekman (1998: 386) commented favorably on Mayr's distinction between open and closed programs in his Afterword to the reprint edition of C. Darwin's The Expression of the Emotions in Man and Animals.
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