Re: Do people in india play around in and drink from the Ganges with no serious ill effects? I’m pretty sure I’d drop dead from coming within smelling distance to the Ganges River. It’s full of feces, garbage, and dead bodies…
In the parts of northern India around where the Ganges is, health conditions and standard of living are atrocious. Educated people and those who can afford otherwise don’t drink from the Ganges. Some people do, and those people certainly aren’t living well. Which is why providing clean water is so important.
Most animals also don’t live as long as we do (with some exceptions- giant clams, Aldabra tortoises, macaws, etc.).
Short answer:
Population boom and fast advancement over the globe couldn’t offer us enought to
time due adapt fast enough to new pathogens (which are also adapting and mutating faster than we), to make natural selection work very well (since modern medicine and technology fight against it) for evolution to bend us that way.
We outpace and conflict nature in that regard a thousand-fold.
That’s because the third world is no more a natural state than the first world. The people who get sick and die a lot tend to be overcrowded farmers. Their water is filthy because there are too many people leaving feces all around, too close to water sources. Odds are those Africans or Asians in the third world keep cows, pigs, or chickens. the run-off from those animals also contributes to poor water quality. As a result, they tend to have bad water unless they are lucky to live near a source that comes from an uncrowded, clean source. Especially in the third world, the bad side effects of the transition from hunter-gatherer to agriculture is evident.
As mentioned above, we evolved for millions of years as hunter-gatherers in small concentrations, moving from location to location. We’ve only been agricultural for about 10,000 years. We have not fully adapted/evolved to meet the perils of our new lifestyle, and if we keep cleaning the water, we won’t need to and won’t.
Consider the case of the American Indians. The lived (mostly) a seminomadic lifestyle, semi-agricultural, few domestic animals - much less exposure to the hazards of overcrowding, and thanks to a 15,000 mile long march from the nearest other source of human contagion, not a lot of diseases. They also did not until recently have the concentrations, the critical mass to create new epidemics.
Then, the white man arrived bringing cows, pigs, horses, chickens and the pens full of disease that they had rough herd immunity to - but Indians did not. Some estimates, about 90% of the locals died. (As I mentioned in other threads - not because they were more likely to die, but because when everyone in the village got sick at the same time, you were just as likely to die from dehydration and starvation factors during sickness as from simple fever.)
Not just rain barrels, but some of the people I used to work with grew up on remote farms, and those typically get their water from local wells. Water filtered through miles of porous rock for centuries is pretty clean, until some local business starts pumping toxic waste into the water table - or overland flooding one year washes filed manure and pesticides into the well… However, someone who spends every morning shovelling manure out of a barn has probably built up a decent tolerance to a certain set of diseases.
The OP is missing another detail, not all animals have anything like the same range as humans, but this range is artificial in the sense that it can only be maintained by our own intervention - such as heating, clothing and water filtration.
If you really want to strip it all back to the absolute basics, then parts of the worked would not be habitable for humans, just as parts of it are not habitable for tigers, or elephants or whatever.
Evolution is partly, if not mainly, about being suited to the local environment, to such an extent that specific adaptations to it lead to diversification
A sperm cell is analogous to a virus in the sense that it is a genetically foreign body that attacks (“infects”) an egg cell and combines its genetic information into the nucleus, whereupon it directs the egg to undergo certain changes that ultimately lead to the development of an embryo and fetus.
Embryology is actually much more complicated it appears initially. A mother who carries a fetus is actually not much different than a patient who has undergone organ transplant, in the sense that the body is carrying a genetically “foreign” body. Fetal abortion (similar to transplant rejection) would naturally occur had species not developed immune tolerance. Sometimes things go wrong and the mother’s immune system (correctly) views the fetus as a foreign body and attacks it, as it was designed to do.
Also, we could have evolved in other ways.
For example there are surprisingly fragile animals and plants that get killed and gobbled up by all sorts of things on Earth. But they are still around. How? Maybe they simply reproduce faster than stuff can kill them. Maybe they are so widely distributed that the ones getting killed/eaten only represent a fraction of the total population.
Look at the third world. They have very high birth rates, in spite of high infant mortality and shorter lifespans. Stuff like tainted water is killing more of them than people here, but if this dirty water would be so lethal than those types of places would have very few humans about- but they don’t, they tend to be teeming with our species in spite of all the health hazards!
This is an assumption. It’s a big assumption, and probably wrong. You don’t have the evidence to tell how well humans tolerate poor water quality vs other animals. For reasons that I hope are blindingly obvious, we’re going to hear a LOT more about sick people in need of help than we do about rats with diarrhea or leopards with queasy tummies, so you have massive data collection bias. As has been said, if you do a survey of wild animals, you’ll find that nearly all of them are infected with levels of parasites and other pathogens that we humans would find horrifying.
I think you’re also way overestimating how badly off modern, first-world humans would do without modern, safe water supplies. Yes, some people would get sick. Some would die. The majority would still be fine. We humans have decided that letting a significant minority of our population die off is unacceptable. Other species don’t have that luxury.
That said, there are certainly some differences between human digestion and animal digestion. Most wild animals are faced with far more pathogenic challenges in their diet than are humans, with our cooked food and treated water. So it’s reasonable to predict that animals have developed more robust defenses than we have, whether those defenses are genetic or environmental, like keeping certain helpful gut flora around.
Finally, it’s worth pointing out that questions in the form of “Why didn’t trait X evolve?” are fairly pointless, because the answer is always the same: either the necessary mutation never happened, or it did happen, and then died out, presumably through genetic drift. A related point is that evolution never produces perfection; it only produces “good enough to survive and reproduce”.