A Catchy Phrase, But is It True?
Esther Jackson is the Public Services Librarian at The New York Botanical Garden’s LuEsther T. Mertz Library, where she manages Reference and Circulation services and oversees the Plant Information Office. Richard Abbott, Ph.D., is a botanist at the Botanical Garden, where he works primarily on updating the Manual of Vascular Plants of Northeastern United States and Adjacent Canada.
Ontogeny recapitulates phylogeny doesn’t exactly flow off the tongue unless you are familiar with scientific terminology. However, what appears to be a somewhat intimidating phrase is actually marvelously succinct and elegant.
Ontogeny is “the development or course of development, especially of an individual organism.” This could refer to the development of a plant from embryo to seed to seedling to mature, reproductive plant. Or it could refer to an animal growing from an embryo into an infant and then into an adult.
Phylogeny is “the evolutionary history of a genetically related group of organisms, as distinguished from the development of the individual organism.” Sometimes these relationships are illustrated as trees of information, with groups of closely related organisms called clades. Studying and depicting shared evolutionary history is known as cladistics. Have you seen Darwin’s tree of life?
If so, then you understand the basic idea of phylogeny. It’s all about the study of relationships.
More than just a catchy phrase, “ontogeny recapitulates phylogeny” is the foundation of recapitulation theory. Recapitulation theory posits that the development of individual organisms (ontogeny) follows (recapitulates) the same phases of the evolution of larger ancestral groups of related organisms (phylogeny). Applying this theory loosely, a seedling of a recently speciated flowering plant (something that recently evolved to be a species) would, throughout its embryological development, mimic the morphology of more ancestral plants—or plants that evolved in earlier times. In theory, then, a young flowering plant might go through developmental stages that look like a moss (or early land plant), then a fern (or other vascular plants), then a gymnosperm (or other seed plants), and so on. Of course, this is not really true, but the implication is that there may be embryological similarities.
Although there are often developmental similarities that do reflect shared evolutionary history, development (ontogeny) does not necessarily reflect (recapitulate) shared evolutionary history (phylogeny). Flowering plants did not evolve from modern gymnosperms, seed plants did not evolve from modern ferns, and vascular plants did not evolve from modern bryophytes. These groups all share common ancestors, which do have features in common, just not necessarily obvious, modern-day appearances.
In the modern cladistics approach to studying evolutionary relationships, similarities that are based on a shared evolutionary history (called synapomorphies) are the most informative when it comes to understanding how two or more organisms are related. For instance, humans share many features with all life (such as DNA) and have more than a thousand genes in common with bacteria. We have even more in common, however, with progressively more “advanced” animals (such as spinal cords, bones, four limbs, and hair), to which we are more closely related.
Recapitulation theory is just that—a theory. The idea that ontogeny recapitulates phylogeny has been used not only by some in the biological sciences, but also by those in the social sciences. It’s easy to understand why the phrase has such pull. It’s succinct and melodic in a way we want the natural world to be. The theory brings a certain amount of order to chaos, and perhaps that’s the catch—it’s a bit too orderly, too clean. Biology is nothing if not messy.