Benjamin Auerbach and Charles Roseman published new research on the Inhibitory Cascade Model, arguing the 20-year-old theory is the product of a statistical artifact rather than a good explanation of developmental or evolutionary relationships. This research reveals a new perspective on the topic of developmental and evolutionary segmentation.

New research is significantly revising a widely cited evolutionary model, the Inhibitory Cascade Mode (ICM). Benjamin Auerbach, professor in the Department of Ecology and Evolutionary biology at the University of Tennessee, Knoxville, and Charles Roseman, associate professor in the Department of Ecology, Evolution, and Biology at the University of Illinois – Urbana-Champaign, published their findings in Evolution. 

The ICM, first published in 2007 in Nature, is a theory about how features that grow in a series (or row), such as molar teeth, develop. It claims there is an activating process and an inhibiting process, and the balance of the two determines the size of the feature. The model was postulated using molar teeth, which form in sequence from front to back. The size of traits like molars is predicted in the model using a statistical process of scaling the second and third molars, for example, to the first element of the series, the first molar. 

In their paper, Auerbach and Roseman explored the mathematical and developmental arguments made in support of the model by other researchers. They found that the mathematical predictions made using the model are the result of a flaw arising from standardization, and that there is little evidence to support the presence of factors in development that inhibit the growth of structures the way suggested under the model. 

After analyzing the ICM by evaluating the standardizing measurements of biological data, non-biological data, and stimulated data, they found there is no evidence that the model accurately reflects processes governing development. One of the indicators that the model is flawed is that it was applied to serial traits that do not form in sequence. For example, in the upper limb, the upper arm and hand form before the forearm, but the ICM still predicted the size of these segments even though the developmental processes claimed to underlie the model do not occur in the sequence. Thus, the researchers conclude that the model’s predictive accuracy is due to a mathematical artifact, which explains why it was successfully applied to parts of organisms that appear in a sequence but do not form in sequence. 

This research opens new opportunities for researchers to investigate how development and evolution unfold to structure the patterns of size in segmented parts of organisms. The advancements made in evolutionary developmental biology and perspectives on molar tooth evolution during the past two decades with the ICM will serve as a foundation for further discoveries.

The future of evolutionary and developmental research is now open to new horizons, with Auerbach and Roseman continuing to study how development and evolution inform each other in the generation of variation in organisms.