Cystinuria is NOT a genetic shift allowing tolerance of low protein foods. Rather, it is a defect in the amino acid transport mechanism of all cells (especially in the kidney) that creates difficulty in transporting the COLA amino acids across cell membranes. Normally, cystine is filtered from the blood in the tubules of the kidney, where it becomes part of the constituents of urine. As the urine is transported towards the ureter, water and various molecules are resorbed back into the body. When a ferret has cystinuria, cystine and the other COLA amino acids are not efficiently transported, and remain in the urine. IF the pH of the urine is acidic, if the concentrations of other chemicals in the urine are high, and if the levels of cystine are high, a precipitation cascade ensues that causes the formation of cystine stones. The problem exists regardless of the protein load of the diet, which means you cannot use the excuse of cystinuria to proclaim there is such a thing as too much protein for ferrets. In and of itself, cystinuria would be a benign disease except for the formation of cystine stones. This is NOT an adaptation to a particular diet, and since the precipitation cascade can occur regardless of consumed protein loads, it cannot be effectively masked; SOME number of ferrets will always display the problem if they have the disease. The idea that ferrets, being domesticated, would have different nutritional requirements has been presented many times, usually by pet food manufacturers justifying a high carbohydrate diet. This hypothesis is the cornerstone for all subsequent dietary hypotheses stacked on top of it. If it is falsified, all their other dietary hypotheses fail. So the question is, could domestication have changed the basic digestive physiology of the ferret, driving it towards a lower protein, higher carbohydrate diet? If this single hypothesis is falsified, then pet food maker's entire argument crashes to the ground. In response, I point out that in three published reports (and several under review), introgression (hybridization) between the domesticated ferret and both forms of polecat was seen to be so extensive that a progenitor could not be determined. On this basis alone, whatever changes that "could have" been introduced into the ferret would have been negated by hybridizing to polecats. That is, even assuming such a change to basic digestive physiology could have taken place. ANY person suggesting such a change has the burden of proof, since even tiny changes to basic physiology generally have horrendous negative results. Making such a claim is extremely disingenuous, because it grants credence to a hypothetical change having little or no actual evidentiary support. My response is, prove it or shut up. When I responded this morning to the person who sent me the post, I give a good number of reasons why such a physiological shift could have not taken place. These objections ranged from pointing out that ferrets bred to drink milk would surely be more lactose tolerant than they are, to the observation that as many (or more) historic writers rejected feeding ferrets milk as those advocating the practice. I was about to offer a similar argument here, when it dawned on me that people were confusing "adaptation" with "selection." It is an easy one to make, and it has fooled the brightest naturalists among us. Ferrets are extremely adaptable animals, capable of consuming many different diets in order to survive. Long time readers on this list might remember the ferret that was found living off beer, or the one that stayed alive by eating donuts. How many times has someone from a shelter mentioned the rescue of a ferret that had been given cheap, low-quality cat food for several years, or ferrets only getting cereals and fruits? Ferrets can reproduce while in a state of malnutrition, and can survive for long periods of time near starvation. These are not caused by genetic changes, but by adaptation. Ferrets have adapted to a kibble diet; of that there can be no doubt. However, adaptation is not evidence of selection, human or natural. The digestive system is extremely plastic, adapting itself to local conditions in order to give the best chance to survive and reproduce to the body in which it inhabits. Ferrets will get sick, usually with the runs and an upset stomach if their diet is rapidly changed. This is because it takes a while for the GI tract to readapt to new conditions. Again, if ferrets "evolved" during domestication to a different diet, then the burden of proof lies with those suggesting the change. They have to prove it, which includes coming up with an explanation of why all the hybridization with polecats introduced wild genes into every single system EXCEPT the digestive one. I've talked at great length on cystine stones and I am starting to feel like I am on a carousel. It is obvious that regardless of the facts, some people are going to remain addicted to their carbohydrated ways, regardless of the scientific facts, and there is nothing that I can do about that. As far as I am concerned, this is a horse that has been beaten into a bloody mess, and I have better things to do, like play with my ferrets or teach this one really great kid the lost secrets of darkroom work. Unless something new can be added to this discussion, I think I'll let the rest of the FML pursue this White Whale while I tread water, looking for the casket. Bob C [log in to unmask] "Little Brothers [weasels and ferrets] were sent by the Great Spirit to keep watch of what we do. They rush to whisper our misdeeds into the ear of the Great Spirit." --Northern Plains folklore, recorded 1827. [Posted in FML issue 4789]