When, in our evolutionary career, did we become unable to drink ‘unclean’ water? … and why?
We stopped drinking “unclean” water when we could get “clean” water. You drank what you could get. The “unclean” stuff would kill off the babies and the weak. Everyone left could drink what there was. (New Improved River Water- now with extra cholera!)
Whiskey for breakfast was not uncomon, even for children, when local water was questionable. Admittedly it was weak whiskey. Beer was the more common choice. Tea is also popular because you have to boil the water first.
We were never able to drink ‘unclean’ water.
The gut flora of most people in western countries certainly has a lower tolerance for any bacterial contaminants than people elsewhere, but this is apparently through lack of innoculation. Given time you would adapt to natural water supplies without it killing you. I grew up drinking creek water, complete with cow pats, dead toads etc. This never gave me any problems and still doesn’t. Many people get ill drinking unboiled water but this doesn’t make it truly unclean. This isn’t an evolutionary change, it’s a microbiological one.
Truly impure water with nasties like cholera is mostly a result of high, sedentary population densities. Under the conditions encountered by pre-agricultural people low population densities and nomadic lifestyle meant that the chance of feacal contamination of water supply was low. People have always fallen ill with these diseases but with the advent of agriculture and permanant/semi-permanant towns the incidence would have sky rocketed.
It isn’t every one who can drink from a creek and get away with it I’ll admit, but for those who can, any puddle anywhere (say, in the next town) would surely pose a health threat.
My point is that whilst illness isn’t an impossible consequence for animals (say, a pet dog, used to tap water at home) drinking from a puddle in the next town, it is improbable that illness would result. I am thinking that this must have been true for our species at one time, but not any longer.
If this makes sense to anyone else, at what point in this continuum of ‘evolution’ would the change have occurred? (I think dogs will retain their ability to drink, unharmed, from puddles on the grounds that they are unlikely ever to learn to brew beer or make tea…more’s the pity!)
If your dog were to drink from a puddle on the ground, it very well could get sick. Giardia for one thing. A few other bugs and cooties (bacteria and protozoans), too. If the dog is used to drinking tap water, it doesn’t have the natural resistance, of say- Gaspode built up. Dogs are less affected by odd water because they are always chewing on something pretty gross and dirty.
You drink what you can get, and if it doesn’t kill you outright, you develop an “immunity” to the local water. (Actually it’s an immunity to the things living in the local water.)
-Rue.
** Rue**It isn’t immunity in the normal sense. Apparently when you innoculate you intestines with some new bacterium 99% of the time it can’t outcompete the bugs already in their and it dies. If it survives their are a couple of possibilities. It can multiply exponentially, causing major ilness by releasing loads of nasty toxins and irritants. This leads to illness and diarhoea until it’s flushed out and/or starved to death. Or it can simply settle down into sustained competetition with the existing gut flora. It may wipe out one or two of your resident strains/species, or it could just lead to a lessening of their numbers. If you do this often enough you develop a pretty competitive gut biota that’s adapted to your diet and your water supply.
This gives an added advantage when drinking any water from any supply. Your microbial system is already ‘battle hardened’ and much better able to cope with whatever new invaders you get. They’re unlikely to be able to wipe out the good guys laready in their becsause your good guys are tough and they’ve adapted to your diet, body temp etc. all ready. If the new bacterium can’t wipe out the existing its got to compete with them for food and can’t increase at any great rate. It’s not just your local water supply it protects you from, you actually gain enhanced resistance from any minor waterborne pathogen and probably most major ones like cholera (but I wouldn’t put this to the test).
CidThere’s no reason why a puddle in the next town would pose a health risk. I’ve drunk watre from creeks, dams and town water supplies over pretty much all of Queensalnd and never shown any ill reaction (except for an initial nasty case of flatulence from my first exposure to sulfur-laden artesian water, but I can drink that with no reaction now.) This is attributable to a more competetive and hardier gut flora. This is a major reason why animals don’t often get sick from drinking dirty water. A lack of hygeine has pre-innoculated them with some pretty impressive bugs. At a time when humans also drank from non-sterile water supplies they would also have had an impressive gut flora. The ability to develop this gut flora hasn’t been lost, people in developed countries just don’t make use of it. There’s no reason to believe that at any time in the past our species would have been any better able to handle drinking impure water if they were raised on chlorinated tap water and there’s no reason to believe that you couldn’t begin developing that gut flora now. There has been no evolutionary change that we know of, just a physical change. It’s a bit like saying that North-American Greek office workers burn faster than Greek orange pickers. That’s true, but there hasn’t been an evolutionary change and if the office workers tried to gradually acclimatise themselves then there’s no reason to beleive they couldn’t eventually handle the Meditteranean sun as well as local agricultural workers.