PF (Patricia/Pat) Anderson

A lamb with a gut full of worms will walk past the good grass to eat a bitter plant that kills them, and the only place it ever learned which plant was at its mother's side. Researchers at Utah State University spent years watching this, because nobody believed it. They took lambs carrying a heavy load of stomach worms and offered them two feeds. Plain alfalfa, which a lamb loves. And alfalfa laced with tannins, the bitter, mouth-drying compound that makes stewed tea undrinkable and that happens to be hard on gut parasites. Healthy lambs barely touched the bitter one. Why would they. The wormy lambs started eating it. Then preferring it. They ate more of the medicine the sicker they were, and their worm counts fell. Then the researchers dosed them with a proper wormer, the parasites went, and the lambs went straight back to the plain feed. They took the medicine while they were ill and stopped when they were cured, which is more than can be said for most of the people in a pharmacy queue. The second part is the one that should keep a dietitian up at night. They put lambs on a heavy, bitter diet and offered them a compound that neutralises the bitterness. Lambs that fed alongside their mothers learned to take it. Lambs taken away from their mothers never touched it. Not once. The knowledge of what to eat when something is wrong was being handed down at the trough, ewe to lamb, by example, and a lamb without its mother simply never got the lesson. Shepherds have known a version of this for as long as there have been shepherds. The sick ewe that goes off on her own to the hedge bottom and eats something she ignores the rest of the year. The flock that heads for the rough corner of the field in a wet spring. Nobody wrote it down because it was obvious. In 1928 a doctor in Chicago let babies choose their own food from a tray, and the one with rickets drank cod liver oil until his bones healed and then stopped. It is the same experiment, with wool on. Meanwhile the human version of the lamb is handed a plate diagram, a list of recommended portions and a leaflet on overriding cravings, and told the instinct is the thing that needs managing. The lamb was never given a diagram. It had its mother, a hedge, and enough sense to stop taking the tablets when it was better.