Now I consulted the Taros Campaign book. Of couse Knarlocs and Greater Knarlocs were introduced with this book, and the reference part of the book has quite detailed info about them.
Both are natural species of the jungles of Pech, evolutionary related to Kroot but obviously not "shaped" by them. No specific date of species origin is given of course, but both Knarloc species exist for a long time and coexist with Kroot for a long time. Kroot domesticate and train them, sometimes even hunt and eat (small) Knarloc flesh to gain their hunter qualities.
Greater Knarlocs are also described as evolutionary cul-
de-sacs, so their ancestors possessed greater genetic variability as todays Kroot do. You are what you eat, is more true for Kroot than for anyone else. Choice of food is essential but even for Kroot "not a science" but an instincual choice. In Kroot kindreds, Shapers have a special role in chosing food or declaring it taboo, often decided by smell. So what shapers do, is not fundamentally different to what all animals on Pech do, chose their food instinctively. With their larger brains and culture, Kroot are just better at it than Knarlocs etc. Just to make it clear: None of today's shapers would willingly lead his kindred into an evolutionary cul-
de-sacs, just to save money on a horse or something.
BTW now you understand why offering a Burger to a Kroot is considered an insult