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What word is used to describe differences of individual organisms

How can scientists test their ideas about the origin of the universe if they can't physically interact with or study?

Ascientist separates a population of mice into two groups. what would most likely increase the rate of speciation in this population. a. teach the two groups different tricks b. allow the two groups to breed with each other c. put the two groups in different environment d. have the two groups live in identical ecosystems