As I understand the core argument for paleo, modern man retains what is essentially a 100,000-year old gene map, and many of our current health and psychological issues result from nutritional and behavioral departures from what Grok's genome was optimized for. However, not all paleoanthropologists appear to agree on that premise. This is from a NY Times interview with Chris Stringer on 16 July 2012:
In the introduction to your book, you list the kinds of questions you’re always getting from people. One of them will be the closing question: What is the future of human evolution?
That’s a tough one to answer. There’s a lot of data, not my research, but mainly geneticists have been working on this, and they’ve showed just how many genetic changes there have been in the last few thousand years in the human genome. And this is because we’ve undergone great changes with urbanization, with agriculture, very big changes in lifestyles. And this has influenced our genetic makeup as much as living in the Paleolithic had done. We’ve seen, if anything, an acceleration of genetic changes in humans due to these lifestyle changes. So, I think human evolution has been going on quite rapidly recently, and it’s going to carry on.
Not everyone agrees. My colleague in London, Steve Jones, has argued essentially that evolution has stopped in humans because we are in control of it. We have medical care. Nearly everyone reaches reproductive age. Everyone has enough food and water. So natural selection has been nullified in humans. I disagree with him because, of course, there are still a lot of people in the world who don’t have the best medical care, who don’t have enough food and water. Think of the impact of AIDS in Africa.
So selection is still operating on many human populations just as much as it ever has done, really. Also, all of us probably have 50 mutations in our DNA compared with our parents. So that’s going on every generation as well. We are still evolving. We will continue to evolve.
If, in fact, there have been significant post-agricultural (i.e. Neolithic) changes to our DNA beyond relatively superficial things like lactose tolerance in some populations, do we need to re-think our argument?
I would agree with the second paragraph that human beings are no longer evolving due to natural selection. The moment humans began adapting the environment to suit their needs they no longer adapted themselves to the environment. Essentially, Humans removed natural selection from the human equation when agriculture was invented. At that point, 'survival of the fittest' no longer applied.
As to how quickly, compared to what? Evolutionary change is harder for us to identify because we no longer understand it's mechanisms as it applies to humans. Evolution up to the advent of agriculture meant bioforms adapting to natural conditions. This was achieved by a limited number of bioforms reaching adulthood, breeding, and passing on 'fit' genes. This mechanism is no longer in place as almost the entire human population reaches adulthood and breeds. All genes are passed on regardless of their 'fitness'.
There can even be a case made that we as a species are devolving. IQ's are higher in populations that still live paleolithic lifestyles compared to 'advanced' civilizations. Simply put, 'advanced' civilizations are allowing the less fit portions of their populations to breed at a higher rate than their most fit. Reverse survival of the fittest!
This may sound all like semantics. I don't think anyone can deny that we as a species have changed throughout the centuries. Just go look at a suit of armor in a castle...looks awfully small for a big bad knight.
When you ask the question "Are we evolving?" the important question is "towards what?"
Stated more precisely: "What are the selection pressures on modern humans vs. Paleolithic humans?"
Civilization has exerted extremely strong selection pressure for disease resistance: look at the history of smallpox in the Americas to see what happens when a population selected for that resistance meets one that hasn't been. Civilization has exerted reasonably strong selection pressure against the HLAs associated with celiac: the longer a population has been agricultural, the less common they are. And civilization has exerted strong selection pressure for the ability to be passive and survive starvation, vs. the desire to be rebellious, self-sufficient, and healthy: those who refuse to submit are almost always killed by the reigning authority.
However, civilization has exerted very little selection pressure (relatively speaking) for strength, health, long life, or intelligence -- and when traits are not positively selected for, they tend to disappear. For example, brain size has decreased 10-15% since agriculture, most likely because pushing a plow is much easier than hunting and gathering. (If foraging weren't difficult, we wouldn't have developed such big brains in the first place.)
Are we evolving? Sure. Are we evolving towards an outcome most of us would find desirable? Perhaps not. (And this is amongst the conundrums presented by The Gnoll Credo.)
I had to laugh the above comment, because it reminded me of the movie Idiocrasy. I do find this and interesting topic. Nothing I say is set in stone, but makes for good conversation.
I don't think we're evolving like we used to. We're also trading genes around more than 100 years ago because of the advent of ships, cars and airplanes, making the genealogy insanely hard to track from a anthropology standpoint.
Notice that in other regions, such as Europe, China, Africa, there are traditional foods people eat and ways of living to stay healthy (probably playing to the strength of their population pool's genes as whole). They do not seem to get the volume of immigration from vastly different population pools like the United States. They probably have a tendency to know what the common illnesses are too and how to treat it.
In the U.S. we're a mixing pot and it's encouraged to assimilate. Many traditions and foods are lost in the name of commerce, and convenience. Genes are traded around as well; some from ancestry we do not know we have. It's not a wonder that it's hard to find a diet and lifestyle to play to each of our strengths. I do not think the same type of stabilization in the genes for certain populations will occur like it did in the past unless we stop globalization and population growth.
Old factors of selection: health, fitness, intelligence, fertility.
Results: hunter gather groups, self sufficient, longer life span (if we didn't tear ourselves up and get injured/killed/eaten), fewer numbers.
New factors of selection: fertility, enough intelligence to make money to live on, ability to handle tolerate grain and low protein, socialization (hive like concept/mind due to recent leap in technology and communications).
Results: Performs a specific function in society. Think people who don't know where their food comes from, or how to purify water nor are they interested in it because the time will never come when they need to perform outside their drone group's duties. Just like when I was making homemade chicken noodles in college. A girl from Chicago watched me make it for a while. Then became disinterested and left telling me 'Well, I buy my food.' The concept of why would you need to make food yourself was foreign to her because it wasn't necessary. dependent on other groups, shorter life span due to poorer/few food sources because of overpopulation (Monsanto and rationing), larger numbers.
I think it will take a while for the rest of the world to catch up with what the U.S. is doing, but we're getting there.
The ability to handle grains, sugar, low protein, and inverted Omega 3's and 6's profiles in the diet is a must.
In a normal situation, I'd say an animal population boom would even out before the above adaptation in present in the majority of animals such that it would cause problems in generations in times of plenty. However man can alter his environment and keep things going for a long time before the downturn in population hits. That being said, in times of plenty after the population decline I see lots of people who will be predispositioned to not be able to handle large amounts of grain. They will be too efficient at using the carbohydrate energy, and excess from times a plenty will be stored the excess as fat eventually leading us toward becoming a diabetic species. But who knows, maybe the population plummet will be so hard that those who survive have to work extra hard to survive and reverse the trend? Or not, they might still have the knowledge from before and do the same thing all over again at a faster rate making us weaker as a species until we die out.
Food for thought. Now I'm hungry.
The human genome is designed with a certain degree of structural instability. This is largely a function of DNA repair and maintenance mechanisms conserved across all cell based life. The rate of repair - or corollary, rate of mutation - determines the rate of evolution.
There is evidence to suggest that the rate of DNA repair is inversely proportional to lifespan. If we accept this hypothesis to be valid, a slowing of the rate of human evolution should go hand in hand with an increase in lifespan. There is no evidence that the upper limit of human lifespan has changed.
Importantly, selection pressures have not been reduced but - as others have also mentioned - have altered in emphasis. To use a sociological group dynamic example, physical traits that enabled dominance may no longer be as important a selective trait as emotional and intellectual skills that allow for more nuanced social interactions.
Despite significant changes in the control of our environment there is a competition for finite resources and this factor alone is sufficient to drive selection pressure and maintain evolution.
It's true that culture and our ability to modify our environments has resulted in a neutralization of the classic selection pressures (such as disease and access to adequate nutrition) on humans. In animal populations with low selection pressure overall, we often see genetic and phenotypic diversification. This is really quite remarkable: it means that the likelihood of some portion of the population surviving the moment a significant selection pressure appears is increased.
People like to say that the dinosaurs were wiped out by the mass extinction event of 65 million years ago, but that's not completely accurate. The big animals that needed lots of food were wiped out, but their descendants still live among us as reptiles and birds. That's the legacy of a diverse population that lived under small selection pressures for many years.
"We" are not evolving toward anything -- every individual is a point sample, a result of all the selections and mutations (that last one is important!) that came before. Also important: whatever came before, every person is unique, and I don't mean that in the "everyone is special" sense. Every person is unique because, whatever you get from mother and father, you're lugging around, say, anywhere between 8 and 15 functionally significant mutations that happened during gametogenesis. In that respect, you're different from both of them and from everything that came before.
Harry is right: rate of mutation and the efficiency and quality of DNA repair have as much an impact on evolution as selection pressures.
And Harry (and others) are also right about this: selection pressure is not gone, it has simply changed in nature. Consider the people who choose to go childless, for whatever reasons -- something about their makeup has influenced them, in the current circumstances, not to have children. (Then there are those who are childless due to any number of other factors: reckless behaviour resulting in premature death of the children, or disease, or failure to socialize sufficiently, etc.) In this way, they can be said to not be optimally suited for the conditions, and the genes responsible for these vulnerabilities, under these prevailing conditions, will be gradually selected out of the population.
In humans, selection is now influenced by culture and technology. The ability to form social groups and to cooperate has conferred an enormous survival advantage, but it also means that individuals need to maintain the ability to socialized; that's a selection pressure. In a high technology society, the ability to work and provide for your family also depends increasingly on higher cognition; that's also a selection pressure.
With a global population of seven billion, all of humanity is hurtling toward the really big test: Who will survive when the environmental limits are reached? Or, will we -- collectively -- realize what needs to be done to prevent a cataclysm and find a way to do it?
You could think of that as a kind of cultural natural selection.
While it is true that there have been genetic changes in the last 10,000 years, and while it is also true that the population continues to change, it's undeniable that big portions of what most humans are evolved not simply over the last 100,000 years, but over millions of years, and a great place to see that is in the brain: going inward from the cortex towards the brain stem is like taking a trip through time. It's a matter of how you weight things.
I can see no way that the rate of biological human evolution can possibly keep pace with the huge changes to our lifestyle and environment of the last two centuries. The conditions of my life are so vastly different from those of my father that we might as well have lived on different planets.
An evolutionary perspective on biology and behaviour isn't going to lose its relevance as long as we are mortal, reproducing organisms.
Why would lactose tolerance and salivary amylase be "superficial" @Dan? These are the reasons that there are no longer any true Paleos - selective adaptation has made them extinct. There are things about paleos that are worth emulating, but the human race has moved on, and there's no way back evolution-wise. If you inherit amylase and lactose tolerance there's nothing you can do about it. It's in your DNA, and heritable by your offspring no matter how much grass-fed liver you eat or pizza you avoid.