Abstract:
This essay reviews the evolution of two theories proposed in the late 19th century to explain the origin of alternate generations in plants, a crucial paleobotanical event leading to the earth’s dominant vegetation. The antithetic theory and the homologous theory were described well before vital scientific evidence was known that could have prevented their confusion for decades. They developed through argument and speculation, and the use of imprecise terms that often exacerbated misunderstandings. The story of their evolution may serve as an example of how scientific theories change, sometimes in ways that are not realized during the heat of debate.