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| Natural selection is a fundamental mechanism of evolution that describes how traits become more or less common within a population.
Variations in traits arise naturally through gene mutations. Some mutations allow individuals of a population to perform better in their environment, live longer, and have more opportunity to pass on their genes. As those individuals breed, their traits become more common within the population. These traits are said to be naturally selected for. Similarly, variations that have a negative effect and become less common in the population by this mechanism are said to be naturally selected against. Ancestors of the modern horse were smaller and had toes.
Toes allowed these animals to maintain better balance on soft forest floors.
However, as horses began occupying hard, flat plains, having a larger central toe (which eventually evolved into a hoof) yielded better support and faster running speeds.
In this example, larger, faster horses were better suited to outrun plains predators, so hooves and larger size traits were naturally selected for. Conversely, toed horses and horses with shorter legs were not as well equipped to outrun plains predators, so those traits were naturally selected against. Did horses decide to grow longer legs so they could outrun predators?
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Instructions Click Start to run the simulation of mouse populations. Allow brown mice to become at least 75% of the population. Then change the environment to allow gray mice to dominate at least 75%. Do the same for white mice. If one of the types of mice reaches 0, you can click reset to return to the starting populations. Goals Achieve >75% brown mice.
Achieve >75% gray mice.
Achieve >75% white mice.
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| A region with a large, steady population of white mice suggests which of the following?
A significant sample of mice from a field contains equal amounts of brown and gray mice. Which of the following would be a good hypothesis to explain this scenario? Which of the following is correct? Mice develop fur colors to match their environments. Field predators only eat grey or white mice, not brown mice. |
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| Which of the following is true?
If a clean lake has a much larger population of brown fish than blue fish, which of the following could be true? If the lake has equal populations of blue and brown fish, which of the following could be true? If a population of blue fish is in decline, it will always recover as soon as the pollution is cleaned up. In the real world, even after all the brown fish in a clean lake have been eaten by predators, there may still be more brown fish in later generations. |
Instructions You have completed the lesson. You may scroll up to review the lesson. |