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The default position for the human genome is lactose intolerance (why would human mammals ever need to metabolize another mammal's milk?), it's actually a mutation that allows humans to successfully synthesize lactase, the enzyme necessary to metabolize lactose.
Probably. There are lots of mutations that are not widespread. For example, a relatively recent mutation has been discovered that gives some immunity to HIV. It's possible that this could become fixed in populations at risk of HIV where HIV medication is not, or is only sparsely, available. It's not fixed until it, as the name suggests, is, for all intents and purposes, permanently established in the population, so you only know with hindsight.
"The ability to digest lactose into adulthood (lactase persistence) would have only been useful to humans after the invention of animal husbandry and the domestication of animal species that could provide a consistent source of milk. Hunter-gatherer populations before theNeolithic revolution were overwhelmingly lactose intolerant,[17][18] as are modern hunter-gatherers. Genetic studies suggest that the oldest mutations associated with lactase persistence only reached appreciable levels in human populations in the last 10,000 years.[2][19] Therefore, lactase persistence is often cited as an example of both recent human evolution[20][21] and, as lactase persistence is a genetic trait but animal husbandry a cultural trait, gene-culture coevolution in the mutual human-animal symbiosis initiated with the advent of agriculture.[22] In Northern European populations, the spread of the lactase-persistence allele is most closely correlated with positive selection due to added vitamin D into the diet. Whereas in African populations, where vitamin D deficiency is not as much of an issue, the spread of the allele is most closely correlated with the added calories and nutrition from pastoralism.[2]"
Some people are known to have immunity to HIV and they also have dual copies of a mutated gene that changes a cell receptor protein that HIV needs to infect cells. See The Evolving Genetics of HIV. Occasionally it is that simple.
I don't know the details of those. Probably they'd revert to metabolising the old diet. It depends on what has changed - if they evolved a cellulose breakdown pathway in addition to the existing pathways (a new enzyme perhaps), they might be able to just switch the old system back on (some bacteria have 'switchable' metabolic pathways, depending on what's available). If their existing pathway(s) had been substantially modified, they'd need to repopulate from regressive mutants. Or they might die out - but, in general, the populations are so large and reproduce so rapidly, with a consequently large number of genetic variations, that I'd expect them to persist.
Because the allele codon sequence in that lineage varies from that of the rest of the population in a manner consistent with known forms of mutation. See Evolution of CCR5 Allele & Evidence for a Single Mutation for a brief summary.
Yep, and Archeans remain Archeans, and Eukaryotes remain Eukaryotes. No problem with that. A hallmark of evolution is that species necessarily remain within their ancestral rank.
Amphibians are really just fish that have evolved to be sufficiently different (limbs, living out of water, skin respiration, etc) to justify their own clade or class. Even today there are eleven different genera of fish ('amphibious fish') that demonstrate various stages of that kind of transition (mudskippers, rockskippers, eels, labyrinth fish, etc).
Quite likely (depending what you mean by 'seen'). Consider how many generations it would take for even a strongly beneficial mutation to become fixed in even a small human population. The Kuru immunity mutation is a possible candidate, although there may be better ones.
There's all that talk again. Take it this way, twist it around that way, then turn it under sideways down, and add a few more words until you have convinced yourself you really have a point. The epitome of Atheist speak.
I'm very serious.
Enjoy!
