The Lesser Apes-Evolutionary and Behavioural Biology.

which consists of three steps: 1) An individual produces a new behavior that permits a novel exploitation of the environment. Such behaviors may be nongenetic in origin. 2) Social transmission permits the rapid, nongenetic spreading of the new behavior throughout the population. 3) As a consequence of adopting a new behavior, the species faces new selective pressures favoring those genetic combinations that improve the individual's effectiveness at a novel environmental interaction. This mechanism is most effective among organisms with a high potential for behavioral innovation and communication. Population structures conducive to the spreading of novel behaviors among populations of varying genetic composition also may enhance this process by increasing the chances that favorable genetic combinations will be encountered. Sage et al. suggest that an unique feature of fish species flocks may be the opportunity for communication of new feeding behaviors beyond the species boundary. They note three potentially important consequences of this transmission: 1) The probability of a morphological response to a new feeding behavior is higher if the message spreads to many species rather than being confined to the species in which it arose. 2) The spread of a new feeding behavior to several related species should elicit parallel morphological responses. 3) The new habit can be tested against a variety of genetic, anatomical and behavioral backgrounds. This hypothesis suggests further evaluation of the existence of interspecific communication within fish species flocks. The effects of various internal and external factors on evolutionary rates may be evaluated most effectively using an historical perspective. Construction of a phylogenetic scheme for the species studied is the first step in this process. Changes in the factors being analyzed can be partitioned on the tree, and one can ask whether fixation of a novel biological feature or entry into a novel environment accompanies or precedes increased evolutionary rates on a particular lineage. In their evaluation of factors that may promote rapid speciation or morphological change, several authors in this book appear to take too deterministic a view of the relationship between the factors being analyzed and evolutionary rates. The origin of a factor or combination of factors that facilitates rapid evolution will not necessarily produce rapid evolution in every instance. The historical analysis suggested here will help to identify factors which appear, on the average, to accompany or to precede the occurrence of rapid evolutionary change in the phylogenies of particular groups.