Natural Selection

Natural Selection

Natural Selection
Reading Level

	edHelper's suggested reading level:	grades 9 to 12
	Flesch-Kincaid grade level:	8.82

Vocabulary

	challenging words:		evolution, mutation, better, surprising, unfavorable, accumulate, variation, biologist, explanation, differ, occur, direct, newly, equal, process, environment
	content words:		Alfred Russel Wallace, Since Darwin, Galapagos Islands

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Natural Selection
By Cindy Grigg

¹     In 1858, Darwin and another British biologist, Alfred Russel Wallace, proposed an explanation for how evolution occurs. The next year, Darwin elaborated on this and his observations in a book called The Origin of the Species. In his book, Darwin explained that evolution occurs by means of natural selection. Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Darwin identified a number of factors that affect the process of natural selection: overproduction, competition,, and variations.

²     Most species produce far more offspring than can possibly survive. This is overproduction. In many species, so many offspring are produced that there are not enough resources like food, water, and living space for all of them. For example, each year a female sea turtle may lay more than one hundred eggs. If all the young turtles survived, soon the sea would be full of turtles. Darwin knew that this doesn't happen. Why not?

³     Since food and other resources are limited, the offspring must compete with each other to survive. Competition doesn't usually involve direct physical fights between members of a species. Instead, competition is usually indirect. For example, some turtles may fail to find enough to eat. Others may not be able to escape from predators. Only a few turtles will survive long enough to reproduce.

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