Put on your thinking caps!
That's an idiomatic expression used by American schoolteachers to encourage children to give careful consideration to a particular problem.
The standard version of the Neo-Darwinian theory of Bilaterian evolution asserts—implicitly but emphatically—that during the ~550 million years of Bilaterian history there was no need for a feedback loop connecting the smallest components of the developing animals—the individual somatic cells—to the entities controlling the production of those cells—the evolving gene pools. My proposed major additive amendment to that theory asserts, to the contrary, that because of the spectacular complexity found throughout the Bilateria and the exquisite precision of cellular construction evident during development of all individual specimens, a theory pretending to explain their existence demands it. I have concluded that such a feedback loop has existed since the origin of the Ur-Bilaterians and that it has played a critical, central role throughout evolutionary time.
Feedback was initiated by lethal juvenile cancer, a process that began in a single somatic cell, a cell that had been imperfectly developed. We can assert that the pre-malignant cell—at a point in time concurrent with (or immediately prior to) its transformation to the cancerous state—was always maldeveloped; carcinogens are mutagens and mutagens are carcinogens. (1) Cancer never begins in perfectly-formed cells.