Biology  5/e   Raven/Johnson
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Natural selection: Natural selection is the mechanism behind the process of evolution. Individuals in a population are selected for or against depending on what traits they have. Individuals with traits that make them well adapted to their local environment are selected for. They tend to live longer and produce more successful offspring than those individuals that are less well adapted. As the successful individuals pass on their genes to their offspring, and the unsuccessful ones don't or do so at a slower rate, the proportion of successful or well-adapted genes and individuals in the population increases over time and generations. Evolution occurs because of natural selection.

Adaptation: An adaptation is a trait that makes an organism more likely to survive and reproduce in its particular environment. The process of adaptation involves the progressive genetic change in a population over time. As stated above, some members of a population have characteristics that make them able to survive longer and produce more offspring than other members of the population (i.e., they are better adapted). Their offspring inherit these traits, so they too survive longer and reproduce more. Gradually, over many generations, the favored traits become more and more common in the population. This is how new species are formed. Behavioral adaptations can be as important as morphological and physiological adaptations in determining the success of various animals.

Animal Behavior: Behavior is defined simply as the way an organism responds to a stimulus in its environment. The behavior of animals, their quick and often complex reactions and interactions, is one of the key features that distinguishes animals from members of the other kingdoms of life and is one of the reasons we find them so fascinating. To understand the behavior of an animal, we must also understand its genetics, its hormonal condition, its physiology, its morphology, and its ecology.

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