As the horizons of science have expanded, two main groups of scientists have emerged. One is the pure scientist; the other, the applied scientist.
The pure or theoretical scientist does original research in order to understand the basic laws of nature that govern our world. The applied scientist adapts this knowledge to practical problems. Neither is more important than the other, however, for the two groups are very much related. Some times, however, the applied scientist finds the "problem" for the theoretical scientist to work on. Let’ s take a particular problem of the aircraft industry: heat-resistant metals. Many of the metals and alloys which perform satisfactorily in a car cannot be used in a jet-propelled plane. New alloys must be used, because the jet engine operates at a much higher temperature than an automobile engine. The turbine wheel in a turbojet must withstand temperatures as high as 1,600 degrees Fahrenheit, so aircraft designers had to
A. the horizon changes its size from year to year
B. science has developed more fields of endeavor
C. scientists have made great progress in studying the horizon
D. scientists can see further out into space
Over the years, biologists have suggested two main pathways by which sexual selection natural selection for characters that confer success in competition for a mate as distinguished from competition with other species; also: the choice of a mate based on a preference for certain characteristics may have shaped the evolution of male birdsong. In the first place, male competition and intrasexual selection produce relatively short, simple songs used mainly in territorial behavior. In the second place, female choice and intersexual selection produce longer, more complicated songs used mainly in mate attraction; like such visual ornamentation as the peacock’s tail, elaborate vocal characteristics increase the male’s chances of being chosen as a mate, and he thus enjoys more reproductive success than his less ostentatious rivals. The two pathways are not mutually exclusive, and we can expect to find examples that reflect their interaction. Teasing for microscopic examinatio
A. showing that intrasexual selection has a greater effect on birdsong than does intersexual selection
B. contrasting the role of song complexity in several species of birds
C. describing research confirming the suspected relationship between intersexual selection and the complexity of birdsong
D. demonstrating the superiority of laboratory work over field studies in evolutionary biology
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