Concept 1.3 Biologists explore life across its great diversity of species Biology can be viewed as having two dimensions: a “vertical” dimension covering the size scale from atoms to the biosphere and a “horizontal” dimension that stretches across the diversity of life. The latter includes not only present-day organisms, but also those that have existed throughout life’s history. Living things show diversity and unity. Life is enormously diverse. Biologists have identified and named about 1.8 million species. This diversity includes 5,200 known species of prokaryotes, 100,000 fungi, 290,000 plants, 50,000 vertebrates, and 1,000,000 insects. Thousands of newly identified species are added each year. Estimates of the total species count range from 10 million to more than 200 million. In the face of this complexity, humans are inclined to categorize diverse items into a smaller
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