We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
...people today are genetically more different from people living 5,000 years ago than those humans were different from the Neanderthals who vanished 30,000 years ago, according to anthropologist John Hawks of the University of Wisconsin. (Reuters)
We were puzzled by the report about accelerating evolution in humans. Didn't seem to make sense because one would think that the power of selection would diminish as mankind controls and creates his own environment.
But it turns out that one of the authors of the suddenly-famous study is on our blogroll - paleo-anthropologist John Hawks. In a blog entry, Why Human Evolution Accelerated, he begins to explain the theory. It's all about population size. Simple math. A quote:
...the ecological changes documented in human history and the archaeological record create an exceptional situation. Humans faced new selective pressures during the last 40,000 years, related to disease, agricultural diets, sedentism, city life, greater lifespan, and many other ecological changes. This created a need for selection.
Larger population sizes allowed the rapid response to selection -- more new adaptive mutations. Together, the the two patterns of historical change have placed humans far from an equilibrium. In that case, we expect that the pace of genetic change due to positive selection should recently have been radically higher than at other times in human evolution.
Except, of course, that we have no DNA or RNA samples from Neanderthals...
What we do see in populations are things like Island Gigantism and Dwarfism - in which habitat will shift the calorie budget based on availability. Thus in island situations we have seen 'dwarf' elephants that are reduced in size due to selective pressures of reduced food availability on islands. Contrarily in the islands of Oceania we have seen gigantic rat which have the benefit of being scaled to an environment that shifts them up the predator ladder as larger predators lose food source availability... thus they scale up in size.
The fun thing about these is that they are entirely due to habitat and not to genetics, save the 'starter effect' of populations that determines food mass availability for given body mass. Genetically there is very little difference in these animals from their mainland stock. Humans have seen this since the invention of 'indoor plumbing' and 'sanitation' to remove human bodily waste products from the environment. We also eat far better than we did 6,000 years ago due to advancement of this thing known as: agriculture.
Thus, today, those in industrialized nations are: taller, live longer, have much better likelihood to survive past 30 and can worry about such things as 'hair care products'.
Evolutionary theory puts forward a concept known as: genetic drift in isolated populations. We have seen that at work globally where island populations do drift genetically as there is reduced competition for food sources based on parent starting populations. This is a different thing than the gigantism/dwarfism issue, although that may lead to sustained drift due to changes in population size and food availability. When there are large populations in a set environment with no way to put selective pressure on the population for or against any change in genetics you do not get any form of 'evolution'. You can get the build-up of some nasty genetic diseases, actually, but selective pressures usually take care of that.
Finally we are coming to understand the time-based need for isolation to enforce genetic drift away from parent stock, and that also requires high environmental pressures to have happen. Humanity has not only removed the environmental pressures, we have also changed external nutritional factors beyond anything that nature could provide. In such an environment just about anything that can survive will survive. A small lake in California had an initial population of one species of small fish... the lake started to serve as a great place for algae to grow and the fish population exploded. Soon fish without pectoral fins, without parts of their tail and even without such things as a lower jaw started to show up as random genetic events. Anthing that could move and shift water into its digestive tract would survive. I remember the paleontologist professor putting forth that without selective pressure this would continue on...
I chimed in: 'Right up to the first fish that gets some teeth and a taste for its fellow fish.'