How Do New Species Form?

How Do New Species Form?

How Do New Species Form?
Reading Level

	edHelper's suggested reading level:	grades 6 to 8
	Flesch-Kincaid grade level:	9.71

Vocabulary

	challenging words:		evolution, separation, continental, selection, marsupial, evolve, world-wide, australian, natural, theory, landmass, lead, unique, pouch, cause, evidence
	content words:		Galapagos Islands, Grand Canyon

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How Do New Species Form?
By Cindy Grigg

¹     Darwin's theory of evolution by natural selection explains how variations can lead to changes in a species. But how does an entirely new species evolve? Since Darwin's time, scientists have come to understand that geographic isolation is one of the main ways that new species form. Isolation, or complete separation, occurs when some members of a species become cut off from the rest of the species.

²     Sometimes a group is separated from the rest of its species by a river, volcano, or mountain range. Even an ocean wave can separate a few individuals from the rest of the species by sweeping them out to sea and later washing them ashore on an island. This may have happened on the Galapagos Islands. Once a group becomes isolated, members of the isolated group can no longer mate with members of the rest of the species.

³     A new species can form when a group of individuals remains separated from the rest of its species long enough to evolve different traits. The longer the group remains isolated from the rest of the species, the more likely it is to evolve into a new species. For example, the Abert squirrel and the Kaibab squirrel live in the forests of the Southwest. About ten thousand years ago, both types of squirrels were members of the same species. About that time, a small group of squirrels became isolated in a forest on the north side of the Grand Canyon in Arizona. Over time, this group evolved into the Kaibab squirrel, which has a distinctive black belly. Scientists are not sure whether the Kaibab squirrel has become different enough from the Abert squirrel to be considered a separate species.

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