Marcus did mind delay, but it was worse not knowing. He waited.
"I have it," said the robot after an interval. "There is great difficulty feeding a city this large. In fact, there is with all of Earth—it's greatly overpopulated."
"So I understand," mumbled Marcus.
"The trouble began forty-five or fifty years ago with the water supply," said the robot. "It was sanitary, but there was too great or not great enough concentration of minerals in it. Information isn't specific on this point. The robots in control of the tanks found that beef, pork, lamb and chicken in all their variety would not grow fast enough. Many tanks wouldn't grow at all.
"The robots communicated this fact to higher authorities and were told to find out how to correct the situation. They investigated and determined that either the entire water-system would have to be overhauled, or a new and hardier protein would have to be developed. Naturally, it would require incalculable labor to install a new water-system. They didn't recommend it."
"Naturally," said Marcus.
"The situation was critical. The city had to be fed. The tank robots were told to find the new protein. Resources were thrown open to them that weren't hither-to available. In a short time, they solved the problem. About half of the tanks that were not growing properly were cleaned out and the new protein placed in them. The old animal name system was outmoded so the new lot number system was devised and applied to every tank regardless of its ultimate origin."
"Then nobody has any idea what they're eating," said Marcus. "But what was that new protein? That's what I want to know."
"It was hardy. It came from the most adaptable creature on Earth," said the robot. "And there was another factor in favor of it. The flesh of all mammals is nearly the same. But there are differences. The ideal protein for a meat-eating animal is one which exactly matches the creature's own body, eliminating food that can't be fully utilized."