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Animals are amazing in all they do to survive, thrive, and propagate. They live in environments that could not support single cells, they extract energy from the environment, they build complex molecules and structures, they alter their environments, and they reproduce. All of these feats and more depend on complex body components that have evolved since the first appearance of multicellular organisms on this planet. What does it take to be an animal?
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Multicellularity enabled the evolution of organisms that are much larger than single-
Organs are composed of four tissue types.