|
Summary |
|
Questions |
|
Media
Resources |
|
21.1 Fossil evidence indicates that evolution has occurred.
|
|
• Fossils of many extinct species have never been discovered. Nonetheless, the fossil record is complete enough to allow a detailed understanding of the evolution of life through time. The evolution of the major vertebrate groups is quite well known.
• Although evolution of groups like horses may appear to be a straight-line progression, in fact there have been many examples of parallel evolution, and even reversals from overall trends.
|
|
1. Why do gaps exist in the fossil record? What lessons can be learned from the fossil record of horse evolution?
2. How did scientists date fossils in Darwin's day? Why are scientists today able to date rocks more accurately?
|
|
|
|
21.2 Natural selection can produce evolutionary change.
|
|
• Natural populations provide clear evidence of evolutionary change.
• Darwin's finches have different-sized beaks, which are adaptations to eating different kinds of seeds. In particularly dry years, natural selection favors birds with stout beaks within one species, Geospiza fortis. As a result, the average bill size becomes larger in the next generation.
• The British populations of the peppered moth, Biston
betularia, consisted mostly of light-colored individuals before the Industrial
Revolution. Over the last two centuries, populations that occur in heavily
polluted areas, where the tree trunks are darkened with soot, have come
to consist mainly of dark-colored (melanic) individuals-a result of rapid
natural selection.
|
|
3. Why did the average beak size of the medium ground finch increase after a particularly dry year?
4. Why did the frequency of light-colored moths decrease and that of dark-colored moths increase with the advent of industrialism? What is industrial melanism?
5. What can artificial selection tell us about evolution? Is artificial selection a good analogy for the selection that occurs in nature?
|
|
|
|
21.3 Evidence for evolution can be found in other fields of biology.
|
|
• Several indirect lines of evidence argue that macroevolution has occurred, including successive changes in homologous structures, developmental patterns, vestigial structures, parallel patterns of evolution, and patterns of distribution.
• When differences in genes or proteins are examined,
species that are thought to be closely related based on the fossil record
may be more similar than species thought to be distantly related.
|
|
6. What is homology? How does it support evolutionary theory?
7. What is convergent evolution? Give examples.
8. How did Darwin's studies of island populations provide evidence for evolution?
|
|
|
|
21.4 The theory of evolution has proven controversial.
|
|
• The
objections raised by Darwin's critics are easily answered.
|
|
9. Is "Darwinism" really science? Explain.
|
|
|
