Unit B

Module 4 Summary



"It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change."

Charles Darwin — The Origin of Species

Evolution is the change in populations over time. Variations are essential to a population's survival. The variations or differences between individuals are created through sexual reproduction and mutations. Populations with greater variation are more likely to survive if their environment changes. Variations that give an organism an advantage are called adaptations.

Two early theorists—Lamarck and Darwin—proposed theories of evolution and population change. Darwin's theory of natural selection is the theory that is widely accepted today, and it is used to explain how nature is involved in population change.

Natural selection dictates that organisms most suited to survive in an environment because of their adaptations will live to reproduce and pass on these adaptations. Today's scientists also have two theories proposing the rate of evolution. The gradualism model describes evolution as a slow, steady, and continuous process whereas the punctuated model describes evolution as a process that occurs in rapid bursts followed by long periods of little change. The speed at which evolution occurs is still up for debate, but scientists agree that populations have changed over time and evolution has occurred.

There is much evidence to support evolution. The fossil record has given scientists information about evolution for many years. Comparative anatomy and embryology are useful tools for distinguishing evolutionary relationships between different species of organisms. Biogeography, genetics, and biochemistry are some other areas of study where evidence for evolution can be found.

In order for change to occur, variation must be present in a population. There also must be environmental changes that encourage natural selection. Finally, there must be reproductive isolation. Barriers, such as geographical isolation or biological isolation, effectively prevent two populations from interbreeding. Over time, each population adapts to its environment. If the adaptations have become so different that successful mating will not occur, then speciation has taken place.

 Assessments

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