<p>About one hundred years ago, the law of homologous series, a sweeping generalization proposed by N. I. Vavilov at a plant breeders’ congress, caused a sensation, so much so that the audience thought they had witnessed the unveiling of something as revolutionary as the periodic table of Mendeleev. Vavilov postulated that the enormous diversity observable in plant forms masked an underlying similarity, one revealed in parallel variations among closely or distantly related plants. In the present article, we consider the law of homologous series from a historical viewpoint and conclude that its unveiling deserves to be recognized as a foundational event in evolutionary developmental biology.</p>