Adam Colby and The Doctor in “Image of the Fendahl”

Are you saying that about twelve million years ago, on a nameless planet which no longer exists, evolution went up a blind alley? Natural selection turned back on itself, and a creature evolved which prospered by absorbing the energy wavelengths of life itself? It ate life, all life, including that of its own kind?

Yes. In other words, the Fendahl. Then the Time Lords decided to destroy the entire planet, and hid the fact from posterity. They're not supposed to do that sort of thing, you know.