genes

I just finished The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending. It's an interesting book, but ultimately hard to review because much of it seems like smattering of anecdotes and speculation. At its cores it attacks the idea that humans haven't changed much since the paleolithic and that the reason our world has changed is because of culture, not genetic change. It's a popular idea and one that's unfortunately associated with evolutionary nutrition. 

I see time and time again this idea that evolutionary nutrition works because we are the same as our ancestors. We aren't the same. As this book points out, genome sequencing shows that the change over the past few thousand years is far greater than this long term rate over the past few million years, on the order of 100 times greater. More controversially, this book argues that the change hasn't been uniform and that there are significant differences between human populations.

This book will upset blank slaters who want to believe that human differences are only skin deep more than it will upset paleo dieters. Why would genes for skin color and nose shape be selected for, and not those for cognitive capacities and digestion of novel foods?

What if we had a time machine and kidnapped a human baby from Stone Age Africa and raised him? Would that baby look, think, or act like a modern human? 

Unfortunately the baby would probably die pretty young. Probably because of human leukocyte antigen, which has been under strong selection from the advent of agriculture. If you are reading this your ancestors way back were probably Middle Eastern or Asian farmers. Their lives sucked. They toiled as serfs day after day. They ate gruel and slept amongst their dirty livestock. They got sick constantly. Many of them died, but some with robust immune systems survived.

By the time we get to the Age of Exploration, their human leukocyte antigens are quite diverse. Which is important, because human leukocyte antigen protects us from disease. Unfortunately they carried those diseases they were at least somewhat protected from over the ocean to a population that had diverged before the advent of animal agriculture (though they had developed their own agriculture). As explained eloquently in Guns, Germs, and Steel, the Amerindians didn't have much good animal stock to draw from when inventing their own forms of agriculture. The germs Europeans brought over killed about 90% of this population.

Other allelles that have been under modern selection are those for serotonin receptors, axon growth, synapse formation, layers of cerbral cortex, and brain growth. And that's just what we know about so far. I have some doubt that the baby would have an easy time with our educational and economic system.

This book also delves into some differences between ethnic populations, particularly the Ashkenazi Jews, which are quite controversial. Even more controversial perhaps is the idea of human domestication. After the advent of agriculture, did elites "domesticate" their peasants through culling/executions/arranging marriages? It's an intriguing idea, but I think the effect is quite limited for reasons I will outline in a future post on agricultural regression. Their other theory that the "bourgeois virtues" have some genetic component seems more realistic to me, but then again it seems most evidence for or against is still mostly in the hypothesis stage, though there have been some tantalizing studies.

Where does that leave the paleo diet? I think it still stands as a valid concept. Start at the beginning and let self-experimentation and science flesh out the rest. Few "paleo dieters" are eating anything that looks much like what we would have eaten in the paleolithic. That's because it's about the premises, not the foods. Paleo diet is about looking at idea, such as the common misconception that saturated fat is bad for us, and asking if it makes since from an evolutionary perspective. I think this evolutionary approach to nutrition will improve as genetic tests do, but right now it's mainly to self-experimentation with a little speculation. 

Some known "recent" genetic mutations and population differences in the book related to food include:

- A gene for salt conservation common in Tropical Africa, but not Eurasia

- Lactase persistence

- TCF7L2 gene variants connected to metabolism, particularly to the pathogenesis of diabetes

- Processing of alcohol, which leds to variable risks for fetal alcohol syndrome between populations

- A fairly rare ApoA-I mutation ( ApoA-Im), which makes its carriers process cholesterol more efficiently

Many of these are connected to ethnicity. Recently I was discussing salt with a friend of Tropical African decent. He said that even cooking with salt at home (the use of salt at home is trivial compared to that used in restaurants or in processed foods) made his blood pressure rise dangerously. For me, if I don't cook with salt my blood pressure gets quite low. I imagine my ancestors on the windy coast of Scotland would have not survived if their salted meat and fish that they relied on had such an effect.

Much of this book is speculation, but much of what went to press in 2009 has turned out to be true. The idea that humans hybridized with neanderthals, for example, has turned out to have a strong scientific basis.

But they hypothesize that the 7R allele of the dopamine D4 receptor, which is thought to be related to the ADHD, was related to farming, when really it seems more related to migration. An interesting take away from the linked paper, Population Migration and the Variation of Dopamine D4 Receptor (DRD4) Allele Frequencies Around the Globe, is that cultures sometimes portrayed as being "wild" have low incidence of this allele.

I guess that brings me to say that this book is very interesting and thought provoking, but it lacks a core to really evaluate for a review. I know a lot of bloggers who have read this book and most of them haven't reviewed it.