Andrew, An interesting question, but perhaps more in the realm of philosophy than genetics?? We already know that most mutations, even minor ones, are ultimately fatal. That is to say, given that most species are extremely well adapted to their environment after millions of years of cumulative change, any additional change imposed upon a species, or upon an individual of a species, especially a randomly selected change, is likelty to "rock the well balanced boat", that is, have a net detrimental effect. Consequently an individual so affected usually dies before reproducing, thereby removing the mutation from the gene pool. When an animal's offspring is "completely changed", that offspring is typically spontaneously aborted, or stillborn, or dies shortly after birth (obviously, medical intervention shifts the balance in some human cases, but animals in the wild don't have that option). Therefore, the chances of an individual surviving a major short-term morphologic change are essentially zero. I don't know just how "major" a change you had in mind. A sinistral Buccinum undatum is the same species as a dextral on. An albino or melanistic or rostrate specimen is the same species as its parents. Apparently some individuals with major morpholigic changes do survive though. We do see quite a few "freak" specimens of fully mature shells. It would be interesting to know how many of these are of genetic origin, and whether any such changes are transmissible to subsequent generations. Paul M.