why is it that bacteria as a species can become immune to an antibiotic (like the skin-eating bacteria the mutated due to anitbiotics) and roaches and other insects as species can become immune to certain insectocides; but humans as a species can’t (that i know of) become immune to common pathogens?
Which “common pathogens” do you mean? Humans are just as capable of developing immunities as any other species.
chicken pox, for one. i don’t mean that an individual human can’t become immune, but just because i’m immune to it won’t make my kids immune to it. germs, on the other hand have become immune to certain atibacterials (says “dr. germ”) and antibiotics.
I’ll assume that by “germs” you mean “bacteria” then. Chicken pox is a viral infection, not a bacterial one.
Not all bacteria develop immunity to a given antibiotic. It is a statistical likelihood that a certain percentage of a population will either be naturally immune or develop an immunity (just like humans) while the rest are killed. Just because one bacillus develops an immunity doesn’t mean all of them will (just like humans). The resistant ones are merely the ones that didn’t die (just like humans.)
It also depends on which species of bacillus concerns you. Comparing a single species (humans) to an entire domain (bacteria) isn’t always valid.
Chicken pox isn’t a good example. It’s in the herpes family, so once you acquire the virus, you have it forever, though it usually stays dormant. You can get recurrances in the form of “shingles” later, though.
The process is a textbook case of evolution. Some bacteria are resistant to an antibiotic, and survive. Some are not, and don’t survive. The ones that survive end up producing the next generation of bacteria, and eventually, without the others to compete against, end up filling up their environment.
This does happen in humans, too, but since we reproduce so much slower, it takes a lot longer with us. It might take thousands or millions of generations for bacteria to show up resistant to something, but thousands or millions of generations of humans is far too long a time for us to track.
Human populations CAN develop genetic resistance to a pathogen, it’s just not that likely.
You need to have a situation where the same pathogen is a relatively big problem over lots of generations.
Now this situation is easy when you’re dosing a population of bacteria with strong penicillin for a couple weeks – that’s thousands of generations with penicillin being the biggest threat to them.
It’s much harder to have with humans. After a few generations (that’s hundreds of years!), it’s likely you’ll have a different pathogen being much more of a threat. Even if the same pathogen is still a big concern, since since it’s lifespan is so much shorter, the pathogen’s population is changing and evolving more quickly than the humans.
Which isn’t to say this doesn’t happen at all. One specific example is historic human populations in African areas with endemic malaria, which evolved resistance to malaria. Bit of a drawback to it, as it increased the chance of sickle-cell anemia, but better than malaria.
And in the long, long, run, the fact that humans have a complex immune system with white blood cells and antibodies and stuff is genetically determined (NOT the specifics of what each person’s immune system is trained to deal with, but the fact that it is there at all). so you could see that as a general evolved resistance to a broad spectrum of pathogens.
This is all a completely different thing that an individual human gaining ‘immunity’ to chicken pox, of course.
Measles. Well, and other diseases, but it’s happened with measles. For us, measles is primarily a childhood illness. You get it, and get sick, with a fever and a rash, but most people recover. While deaths from the disease happen, they’re not usual.
When the settlers came over to the Americas from Europe, they encountered a population that didn’t know about measles, and caused epidemics that killed a large number of people.
AARRGGHH.
Bacteria do not develop immunity AT ALL. What we call immunity in bacteria is properly called RESISTANCE. An antibiotic has a mechanism by which it kills, or prevents reproduction by, bacteria. If a particular bacterium has a mutation that prevents that mechanism from working, that bacterium will survive and thrive and reproduce in the presence of that antibiotic, and all of its progeny will carry the same mutation.
Immunity, in humans, involves antibodies and T-cells and such, none of which are present in bacteria, and none of which are inheritable.