One of the memes frequently tossed about -- especially by promoters of the various "caveman" diets -- is how "we" (meaning all human beings) have not evolved since Upper Paleolithic times, and that illness results from our failure to limit our diet to what our Cro Magnon ancestors ate. The premise is that thousands of years of daily consumption of dairy products by ethnicities in some regions, or lots of rice in others, or lots of fish in others -- had no effect whatsoever on the evolution of these populations. Not to knock the possible health benefits of the Caveman Diet, but I've always been a bit skeptical of that particular premise, because if you think about it, modern medicine has only been around for a century or so, and as there was no one to diagnose or treat health problems caused by food, the people who couldn't hack their prevailing regional diets were unlikely to live long enough to contribute to the gene pool. But what the hell do I know? I have not studied human genetics in sufficient detail to know for sure. Not that a little thing like that would stop people who are not geneticists from saying they know we have not evolved, and that we should return to eating raw meat (preferably from wild animals killed with our bare hands....)

Anyway, this piece about dog genetics is a reminder that evolution might occur a lot more rapidly than most of us realize:

Like humans, dogs are more than 99 percent genetically identical to one another - despite a lot more diversity in shapes and sizes.

When scientists examined the head shapes of different breeds, they found as much diversity in dogs as existed across the much wider group of animals called carnivora - which includes walruses, cats, skunks, and weasels as well as dogs.

That was surprising, considering how fast this diversity came about in dogs, said biologist Abby Drake, lead author of the study. Most of the 400 known breeds emerged in just the last several centuries.

And yet they haven't branched off into different species: Technically, most breeds can produce fertile offspring with any other breed (though size differences might make it tough for some).

Humans have allowed some of this variety to come about by interfering with the normal workings of natural selection - thus allowing all kinds of things that might not last long in the wild. Imagine Chihuahuas or miniature poodles competing against wolves. "It's a massive evolutionary experiment we've conducted," Drake said.

Asians tend to be allergic to milk and milk products. This is because of lactose intolerance:

Lactose intolerance is the inability to metabolize lactose, because of a lack of the required enzyme lactase in the digestive system. It is estimated that 75% of adults worldwide show some decrease in lactase activity during adulthood.[1] The frequency of decreased lactase activity ranges from as little as 5% in northern Europe, up to 71% for Sicily, to more than 90% in some African and Asian countries.[2]

....certain human populations have a mutation on chromosome 2 which eliminates the shutdown in lactase production, making it possible for members of these populations to continue consumption of fresh milk and other dairy products throughout their lives without difficulty. This appears to be an evolutionarily recent adaptation to dairy consumption, and has occurred independently in both northern Europe and east Africa in populations with a historically pastoral lifestyle.[10] Lactase persistence, allowing lactose digestion to continue into adulthood, is a dominant allele, making lactose intolerance a recessive genetic trait. A noncoding variation in the MCM6 gene has been strongly associated with adult type hypolactasia (lactose intolerance)[4].

But I try to keep an open mind about these things. Perhaps I should sample some fresh road kill and see whether I feel better.

ADDITIONAL NOTE: I realize that what we call "processed foods" (especially milled flour, sugar, and the various preservative-laden fast foods) are of recent origin, and that "we" have not had time to adapt to them genetically. But this does not mean that they would affect all people the same way. Nor does it necessarily follow that because they are new and we have not sorted out the evolutionary implications, that they are bad.

UPDATE: Oregon Guy links a fascinating post about the European bison, which makes me wish I'd titled this post "Traditional Pleistocene Values."

MORE: Alan Kellogg links Razib Khan "for a good introduction to the subject of human evolution"; I found this post about rice, alcohol and genes especially fascinating:

....in many pre-modern societies alcohol consumption was very widespread. In societies where nutritional stress was common it was a major source of calories, and as I note above its advantage in terms of low pathogen load vis-a-vis water was probably a major factor in its healthful effects (many ancient societies mixed water and wine freely). Not only does alcohol provide energy, but its psychological boost is obvious when it comes to the grinding life of a farmer. Rum rations was one of the major factors which allowed Caribbean slavery to be as economically profitable as it was, its existence made the short and brutal lives of human chattel more tolerable. The attraction of people who had little experience with alcohol, in particular its more potent varieties, to the substance seems a clear signal that once discovered it would inevitably exhibit a magnetic appeal. In this case the bias in favor of those who were more metabolically suited toward processing the new source of calories with the least deleterious consequences would have a great fitness consequence.

"We" are not all the same.

If you are one of those mean-spirited people who hates "good" veggies like Brussel Sprouts or broccoli, did you ever wonder why?

That, too, might be evolutionary -- natural selection favoring the survival of humans who avoided bitter tastes:

MADRID - Spanish researchers say they're a step closer to resolving a "mystery of evolution" -- why some people like Brussels sprouts but others hate them.

They have found that a gene in modern humans that makes some people dislike a bitter chemical called phenylthiocarbamide, or PTC, was also present in Neanderthals hundreds of thousands of years ago.

The scientists made the discovery after recovering and sequencing a fragment of the TAS2R38 gene taken from 48,000-year-old Neanderthal bones found at a site in El Sidron, in northern Spain, they said in a report released Wednesday by the Spanish National Research Council (CSIC).

"This indicates that variation in bitter taste perception predates the divergence of the lineages leading to Neanderthals and modern humans," they said.

Substances similar to PTC give a bitter taste to green vegetables such as Brussels sprouts, broccoli and cabbage as well as some fruits.

But they are also present in some poisonous plants, so having a distaste for it makes evolutionary sense.

"The sense of bitter taste protects us from ingesting toxic substances," the report said.

Antifreeze has a sweet taste, which appeals to animals and children. A dog can walk through antifreeze spilled on the driveway and ingest a fatal amount just from licking its paws clean.

AND MORE: "Human evolution speeding up."

Why it would have stopped 20,000 years ago, no one has explained.