1. (biology) a hypothesis of directed evolution (as opposed to natural selection of random variations)

Encyclopedia: Orthogenesis

• hay fever
• hay-scented
• hay-scented fern
• Hayastan
• haycock
• Haydn
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• Hayes
• hayfield
• hayfork
• haying
• haying time
• hayloft
• Haym Salomon
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• Hayti