Scientists puzzled for two decades over this seemingly unnecessary withholding. Now researchers, including Princeton's Djabrayan, Shvartsman, Smits, Krajnc, and Stern have shown that the inhibiting mechanism, controlled by an enzyme known as RNR, is key to the embryo’s survival. Too much material early on leads to disaster for the fledgling lifeform.

“This study shows us how fragile development can be,” said Stanislav Shvartsman, professor of chemical and biological engineering and the Lewis-Sigler Institute for Integrative Genomics at Princeton. “We asked the question, ‘Why does the mother have to be so frugal?’” The problem led Shvartsman to test what happens when an embryo inherits an abundance of these building blocks. The answer was not pretty. “We realized, if you do not limit the supply, you create a temporal conflict that disrupts multiple processes in the embryo,” he said.