Expanding clusters of cells are commonplace in the natural world, and depending on the context, they may be beneficial or harmful to humans. Understanding the impact of cell groups on their environment requires that we understand evolution within such cell populations.

Some cell behaviors -- especially those that give the cell group its ability to exploit environmental resources -- are cooperative in nature, and whether or not such behaviors evolve depends on how the group is structured. When genetic relatives are clustered together, cooperative cell behaviors like extracellular enzyme secretion can evolve more easily. Secreted enzymes, in turn, may allow a pathogenic bacterial colony to become more virulent, or a nascent cancerous tumor to become malignant.

Using a computer simulation framework that implements independent cells in explicit space, we have shown that the internal structure of cell groups can depend very heavily on the environment. In the three images shown here, the red and blue cell types do not differ in any way other than their color, which is used to determine whether a cell group remains well-mixed, or whether related cells tend to cluster together.

From left to right, environmental nutrient concentration was decreased from ubiquitous, to moderate, to sparse. As nutrient concentration decreases, the tendency for different genetic lineages to spontaneously segregate increases, which favors the evolution of cooperation. This result may inform our understanding of pathogenic cell groups, in which cooperation between cells is harmful for their host.