When organisms live in similar environments they often become modified by natural selection in similar ways. This is called convergent evolution. In the deserts of the southwest U.S., one finds members of the cactus plant family. Adaptations to the desert environment exhibited by these plants include a loss of leaves, the development of photosynthetic stems, and the possession of thorns as a predator deterrent. In the deserts of Africa there are plants that look very much like cacti, but they are actually members of a different plant family, the euphorbs. Euphorbs that are not found in the desert look nothing like cacti. The euphorbs that live in the desert look like cacti because they face the same selection pressures from the desert environment.

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