Rock, Paper, Scissors - can cyclic dominance explain diversity of species and individuals?

August 27, 2020

Evolution theorists at the Max Planck Institute for Evolutionary Biology have developed a computer simulation model that can mathematically explain and prove the rare occurrence of cyclic dominance in nature. Mathematical models can thus support ecological research.

One of the unsolved mysteries in the theory of evolution is the enormous diversity of individuals in nature, not only between species but also within a species. Actually one type should prevail and dominate all others.

However, if one takes a closer look at dominance relationships in evolutionary theory, it is obvious that it is not always so clear who is dominated by whom and who is subordinate. An example of this is so-called "cyclic dominance", which can easily be illustrated with the well-known game "rock, paper, scissors": scissors cut paper, paper wraps rock, rock grinds scissors. A "cycle of dominance" emerges, each of the hand gestures dominates and is dominated at the same time. What is shown here in a three-way constellation can in theory be extended to any number of different types. For some scientists, this is an explanatory model for the diversity and balanced coexistence of many different species.

But there is a catch: In nature, only a few examples of cyclic dominance within a species have been documented. One example in microbiology is toxin-producing E.Coli - cells that can destroy other cells that react to the toxin. The poisonous cells are in turn dominated by those cells that do not react to the toxin. The poison-sensitive cells can then dominate the resistant cells again, since they no longer have to fend off the poisonous cells. Thus a dominance cycle is created. There are also other examples described in biology, but overall these observations remain very rare. Why is this so?

The evolution theorists Hye-Jin Park, Yuriy Pichugin and Arne Traulsen have now developed a computer simulation model that can mathematically explain and prove the rare occurrence of cyclic dominance in nature. In this model, new mutations and thus types constantly occur in a population. The research team was able to show that cyclical dominance in the simulations as a whole rarely arose and persisted, and the more similar the individuals are, the rarer they are. "It is difficult to evolve cyclic dominance within a population. It is somewhat easier when new types migrate into a population. But meeting the conditions for this is not easy," says Hye-Jin Park, a recent professor in Pohang, South Korea. These simulation experiments can therefore explain the rare occurrence of cyclic dominance in nature.
These research results are a good example of how ecological observations can be supplemented and substantiated by evolutionary theory calculations and models.

Research Group Evolutionary Theory

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