TPNS 6: A Novel Pitch for Low Carb

Primitive Nutrition 6:
A Novel Pitch for Low Carb

If you want to breathe new life into the tired old low carb idea, you're going to need a fresh way to scare people away from carbs.  The unique innovation that Paleo brings to the low carb business is the claim that grains and beans were first eaten too recently to be something our bodies can handle now.

In Paleo-speak, these foods are evolutionarily novel.  I think this view is composed of three assumptions.  The first is that these foods were new for humans 10,000 years ago. The second assumption is that some major adaptations to these foods were necessary. The third is that 10,000 years wouldn't have allowed enough time for these adaptations to become established in our population. If we grant that a typical human generation was around 20 years, then 10,000 years makes for 500 generations.

To address the first assumption, we’ll need to fact check their history.  Here is evidence of cereals being consumed 19,000 years ago.  That amounts to 950 generations.

Here is evidence going back 23,000 years.  That's 1150 generations.

And here is evidence going back 30,000 years.  These authors call grain use commonplace and widespread across Europe.  Now we're up to 1500 generations.

There is even some evidence that grains were consumed as long ago as 100,000 years. Now we're up to 5000 generations.  So much for that first assumption.  The second, that adaptations to beans and legumes were necessary, I will address in just a moment.

Let's skip to the third assumption, the one saying 500 generations wouldn't have been enough for any important adaptations to become established, if we pretend for the moment that that's the right number.  What evidence is there for that?  Here we see that salmon can undergo reproductive speciation in fewer than 13 generations.

Here are lizards that developed a completely new gut structure that allowed better digestion of a vegetarian diet in only decades.

Here are a few other examples of quick evolution in animals.

What about in humans?   Here you see that Tibetans have evolved a capacity to thrive at high altitudes in only 3000 years.

Native Americans have an adaptation to heat stress that needed as few as 12,000 years to develop, which is in the ballpark.

To scientists not invested in the Paleo diet idea, an insistence that humans have not evolved much since the Paleolithic is not an easy sell.  These authors argue that the speed of evolution in humans has been quickened by the introduction of agriculture.

Human cultural change has subjected up to 10% of our genes to positive selection within the last 10,000 to 20,000 years.

The famous Paleoanthropologist John Hawks sees a recent quickening of evolution as well.  He says lactase persistence, which allows some people to tolerate milk in adulthood, occurred in less than 5000 years.

I think the Paleo people are under the misapprehension that if blunt natural selection mechanisms have been less strong since civilization began, that somehow means we are not evolving.  Actually, for evolution to happen, there only needs to be different traits with different effects on fitness.  If a trait is advantageous, it should spread through a population faster than a trait that is not.

The concept of fitness seems to confuse Mark Sisson.  Somehow he thinks humans were not subject to positive selection after the agricultural revolution.  I'm not sure where he gets this idea, and I'd be interested to know who the many researchers are who say we are genetically identical to what he calls our primal ancestors, whatever primal means.

This is some of the best material I can find to support Sisson's claim that, as he says, "evolution essentially ground to a halt."  The gist of this article is that maybe evolution has slowed down but it is hard to tell. I haven't seen any scholar outside of Paleo say anything about evolution grinding to halt.

In either case, this Paleo belief creates a paradox.  If you believe it, then on the one hand, the Neolithic suddenly brought an easy life with no struggle to survive.  Evolution halted.

But on the other, human health was stressed in new and devastating ways by bad nutrition.  Should we imagine these nutrition problems did not create selection pressures?  And should we avoid grains because of their troubles?

Paleo thinkers tell us people got shorter and less healthy when they started farming.  They base this on the fact that human remains from back then show shorter stature and signs of nutritional stress.  Not everyone is in agreement about this, but let's just concede this point.

So let's think about this paradox.  Whether it was good for them or not, these people did eat grains.  When a Paleo promoter says these grains were really bad for them, that means they should have been a force of purifying selection.  The worse these foods were for them, the better we should be adapted to them today.  Or, looked at another way, if humans haven't adapted much to grains since then, that means they weren't such a big problem.  This is part of my response to that second assumption, that adaptations to grains and beans were necessary.  Either way, it doesn't help the Paleo idea.  So can we tell which scenario actually happened?  It's hard to say.  Genetic research suggests humans have improved their ability to digest starches since the beginnings of agricultural.  That means that long ago people could not digest these starches as well as we can today, so it was an important issue.  We benefit from this fact today.

But there are more important reasons we see evidence of stress in the skeletons of people who lived through this period.  The most obvious one is that they simply hadn't figured out agriculture yet.  They didn't get things right immediately.  The new agricultural economy created new social and economic stratification that lead to conflict and repression, and this affected health.  Those are hardly purely nutritional problems.

Another factor is that people of this time had not yet developed cultivars that met human nutritional needs the way our crops do today.  To give you a sense of the importance of this, here is a potential range in nutrient densities among varieties of one crop, wheat.

Carrots give us a good example of how the nutrient density of a crop has improved over time.  Visit this page and you'll see carrots have an interesting history.  Wild carrots didn't offer the nutrition of today's cultivated orange carrots.

There were also new stresses from infectious diseases, a byproduct of the greater population concentrations enabled by agriculture.  Infectious diseases need dense populations to spread.  Surely this source of stress affected their health and therefore their remains.

This source also raises another issue.  People also hadn't figured out the need for complementary proteins in their crops.  We shouldn't be surprised that populations trying to survive on a very few staples ran into problems.

Cultures throughout the world have independently come to combine crops to meet their protein needs.  These practices needed time to become established.

It is highly likely your culture has these issues sorted out better than the first farmers did.

Possibly the worst generator of disease in humans since the Neolithic is zoonotic infection.  These are diseases that jump from animal species into humans. The establishment of a sedentary way of life allowed for the domestication of animals for meat and milk.  Zoonotic infections remain a wellspring of pathogens for humans today, from the consumption of bush meat that likely gave humans the HIV virus, to the recent swine flu scare that originated in factory farms.

Past exposure to these diseases has shaped our immune system.

Here's another factor.  Iron deficiency has been observed in human remains from back then.  Parasitic infection was a likely cause of some of this.

Since we are talking about a diet that is based on evolution, we can look to Darwin himself for further insights into the challenges of those days.  He understood the importance of population density.  Populations can't multiply indefinitely. Eventually they are limited by the carrying capacity of their environment.  That carrying capacity is dynamic.  At some point a population will be severely stressed.  People back then would have faced blight or drought with only weak coping strategies.  They also would not have established robust trading systems to buffer them in times of shortages.  Surely this accounts for some the hardships represented in their remains.

One mechanism that would have reduced population density, and therefore disease, for the stone agers was their extremely high levels of violence.  Paleo promoters don't usually mention this side benefit to Stone Age culture.

The violent life of the hunter gatherers might have contributed to selection pressures for body size.  It was more of an advantage to be bigger and stronger in a violent world.  Once agriculture became established and the world became a bit more civilized, males might have become smaller.

Moreover, around the same time, hunter gatherers got smaller as well, in addition to many other mammals.  This is a pretty damaging fact for the Paleo pushers.  Changing climate might have caused this, rather than beans.

With all these far more parsimonious explanations, does it really make sense to blame grains and legumes for causing worse health for the first farmers? From my reading it seems Loren Cordain did not have a lot of company when he first made his case against cultivated crops.  Give him some credit.  At least his idea was evolutionarily novel.

In the next video, I will circle back to the idea that your genes require you to follow a Paleo diet.