Now that I'm retired and living in Spain I get to hear interesting notions from many different people and along with those who are frankly exploiting the fascination with medieval notions of medical causes, otherwise known as scams, there are those who are interested and curious about the natural world. A recent conversation turned to a remarkable report about some sheep that apparently were able to graze on seaweed, despite the high salt concentration. They had been able to adapt to a change in diet thus providing graphic evidence of the reslience and responsiveness of the mammalian digestive system.
Flickr photos of said sheep and wikipedia on the North Ronaldsay sheep of Orkney.
Of course a little thought about diets should convince us of the adaptability. Across the world we have widely divergent diets in peoples who are essentially healthy: for example we have Inuits who live on a very high fat diet of seal, reindeer, whale meat; we have Argentinian cowboys who live almost entirely on meat; we have coastal communities in Japan who live almost entirely on fish; and so on.
Of course these are examples of adaptation and not evolution. If we take an ordinary human and move them to Argentina and get them living on a diet of almost exclusively meat, they will survive and may even be healthier, because their gut will adapt. The difference between this and evolution is a popular misunderstanding.
Evolution requires three things: variation, replication, and selection. That means that it's active across generations, not within them. An evolutionary change in digestion would for example be where a modified enzyme is created in an organism as a result of a genetic mutation in the DNA of one of the parents, responsible for that protein (variation). Then the gene is passed to the offspring (replication) which manifests itself as an ability to better digest a particular foodstuff.
So far there is just a random mutation passed on to the offspring - we don't yet have evolutionary change. For that to happen, we need there to be some selection advantage in the offspring, for example because the climate has changed and the traditional foodstuffs are now in short supply or not available. Offspring containing the mutated gene can produce an enzyme that gives them a survival advantage.
Such a small change can lead to the persistence of the mutated gene in the gene pool with its increased frequency in the population surviving in future generations. Now we have evolutionary change.
Just like it's easy to mistake adaptation for evolution, it's also easy to get taken in by association between potentially unconnected events. I was told of a case of a woman who, unless she drank water from a particular well, would develop gall-stones. The said well was therefore assumed to contain some important mineral that effected the cure or at least kept the illness at bay.
This sort of associative thinking was popular pre-Enlightenment when plausibility sufficed and there were much less stringent demands for evidence and a causal chain of events. When I questioned why such an association was thought plausible I was met with the common response of "Well, it could be true..." Indeed it could, on the same level of plausibility as standing on one leg and whistling is a cure for cancer...
Many of these claims reduce to a question of gullibility. The people who seriously considered the efficacy of brackish well-water as a preventative for gall-stones would also consider themselves to be rational - so where did the gullibility come from?
First we have an assertion of a cure/prevention so we are immediately looking for a recent cause. The teller of the tale identifies drinking the well-water as a significant precursor (establishing the connection), and there is then supporting circumstantial evidence that on ceasing the consumption of the water, the gall-stones reappeared. The credulous now need to find for themselves either a better explanation (which they can't do without some science) or reluctantly accept the irrational. It's made more palatable by the simple statement that there are lots of things we (they really mean they) don't understand. All in all, it's choosing not to think rather than to challenge the palpably irrational.
Once the meme of irrationality gets rooted in a community, evidence is dismissed as unnecessary and the way is open to all sorts of silly therapies, pseudo-medical scams, and medieval hobby fraudsters. But it's all done with refinement and pleasantries - you can be sold a magic crystal by someone who has been on a course and you can bet that it didn't have anything to do with physics!
