Atavism
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In biology, an atavism is a modification of a biological trait's structure or behavior whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous gener
Early embryos of various species display some ancestral features, like the tail on this human embryo. These features normally disappear in later development, but it may not happen if the animal has an atavism.
Prothorax
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The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites are the pronotum, the prosternum, and the propleuron on each s
Atavism
…Dewclaws in dogs. Reappearance of prothoracic wings in insects. Reappearance of wings on wingless stick insects and leaf insects and earwigs…
Prothorax of a beetle