Evolution needn’t make improbable leaps to facilitate transitions into uncharted biological territory. Adapting new uses for existing structures works just fine.
In the prologue to the book, author Neil Shubin sets the stage for discussing the iterative repurposing that marks several transformational developments throughout evolution.
So far, six animal species are known to carry transmissible, “parasitic” forms of cancer, but researchers are still mystified as to how cancer can become infectious.