Animal evolution

Animal evolution is the history of change and diversification in animals through descent with modification, from their earliest ancestors to living species.

Ediacaran biota: A diverse assemblage of mostly soft-bodied organisms preserved in rocks from the Ediacaran Period. Some Ediacaran fossils may represent early animals or close relatives, but their identities remain debated.
Natural selection: Differential survival and reproduction that change the frequency of heritable traits in populations. It favors inherited traits that improve reproductive success in particular environments.
Phylogenetics: The study of evolutionary relationships among organisms using shared characteristics and genetic evidence. Animal history is organized into branching hypotheses of common descent.
Vertebrate evolution: The evolutionary history of animals with a vertebral column, from early chordates to living vertebrates. Vertebrates exemplify major transitions in skeletons, senses, and terrestrial life.
Animal phylogeny: A hypothesis of evolutionary relationships among animal groups. Several deep branches of the animal tree remain difficult to resolve.
Cambrian explosion: A geologically rapid diversification of animal forms during the early Cambrian Period. Its fossils record the appearance of many major animal body plans.
Genetic drift: Random changes in allele frequencies caused by chance differences in reproduction. It can shape animal populations even when a trait offers no selective advantage.
Animal body plans: The structural organization of an animal, including its symmetry, tissues, and major body regions. Comparing body plans helps identify major evolutionary transitions among animal groups.
Tetrapod evolution: The evolutionary history of four-limbed vertebrates and their descendants, including birds and mammals. The move from water to land reshaped vertebrate anatomy and ecology.
Origin of animals: The emergence of animals from single-celled ancestors related to modern choanoflagellates. Fossils and molecular estimates disagree about when the first animals appeared.

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