Victory for the ACT Student Text 15e

S CIENCE R EVIEW • 345

Passage III Jean Baptiste Lamarck hypothesized the process of biological evolution before Charles Darwin was born. Some aspects of Lamarck’s ideas and Darwin’s ideas are presented below. Lamarckism Observations of the fossil record led Lamarck to believe that several lines of descent led to nature’s broad diversity of organisms. Old fossils and recent fossils showed patterns leading to the characteristics of modern species. He believed that newer forms were more complex and more “perfectly” adapted to their environment. New adaptations could arise as the environment changed. Body organs that were used to cope with the environment became stronger and larger, while those not used deteriorated. For example, giraffes stretching their necks to reach higher leaves would develop longer necks. In addition, such changes in structure could then be passed on to offspring (these acquired characteristics could be inherited). 13. A major difference between Lamarck and Darwin relates to their views on: A. the diversity of organisms in the natural world. Ǥ –Š‡ •‹‰‹ϐ‹…ƒ…‡ ‘ˆ ˆ‘••‹Ž•Ǥ C. the importance of adaptations to the environment. D. the way adaptations come about. 14. Which viewpoint supports the idea that present-day species are descended from earlier forms? F. Lamarckism G. Darwinism H. Both viewpoints J. Neither viewpoint

Darwinism Based on the fossil and geologic record, Darwin also came to believe that various modern species were related through descent from common ancestors. He also noted that the great diversity of organisms that he observed during his travels were all very well- adapted to their environments. The adaptations, however, did not come about through “coping” or usage. Instead, individuals from a population can each show slight genetic or “heritable” differences (variability) in a trait. If such differences, by chance alone, give the individual some reproductive advantage (he or she can successfully produce more offspring than other members of the population), then more individuals with that trait will make up the next generation. Through this “natural selection” of individuals with characteristics that give them a slight advantage in their particular environment, species appear to become very well-suited to their natural world. However, “perfection” is not a useful term since the environment is constantly changing. The adaptations that are advantageous “today” may not be advantageous “tomorrow” under different conditions. Which statement might be used by a Darwinist to explain the extinction of a species? A. The environment changed, and not enough individuals had traits or adaptations well-suited to the new conditions. B. The environment changed, and body parts could not be manipulated enough to adapt to new conditions. C. As the environment changed, the individuals present were not “perfect” enough. D. As the environment changed, there was no “natural selection.” 15.

Passage Perfect Be sure to circle or underline the key concepts of Lamarckism and Darwinism so that you can easily compare the two while answering questions. Also, when answering a comparison question about a particular •…‹‡–‹ϐ‹… discipline, it is important to understand the mechanism each viewpoint believes is responsible for the phenomenon as this is likely to be questioned.