Hi Matthew, I'm a cancer biologist, and we use the evolutionary model every day to understand cancer progression at the cellular level.

Inherited changes in tumor cells produce populations that diversify & compete for resources. Over time, selection factors change the cells.

This little scribble in Darwin's notebook reflects the "clonal expansion and selection" of tumor cells that make cancer such a difficult disease to combat.

If you apply artificial pressure with one type of therapy, it inevitably selects for resistance to that therapy.

Over time, the environment of the tumor selects for the most successful variants of the tumor cells: often these are the faster growing, more aggressive tumor cells, but not always.

Sometimes a stealth strategy is selected for.