“I would not dream of denying the evolutionary heritage present in our bodies” - Marlene Zuk, author of Paleofantasy: What Evolution Really Tells us About Sex, Diet, and How we Live
Well, the "paleofantasy" is back again, and this time in full force as a book by Marlene Zuk. When I wrote my last blog post, a biological anthropologist used the same word to describe why people mimicking cavemen were wrong. Which is true, of course. But is Zuk saying anything other than the obvious: 'you shouldn't commit the naturalistic fallacy'?
I'm not sure she's saying anything substantial at all, really. All the true things she says no one disagrees with, and all the false things she says are obviously wrong.
She's proud of a moment she had vs. Loren Cordain after one of his talks. She rendered him speechless when she argued that the Neolithic was plenty of time to adapt to Neolithic foods.
So there's the first assertion: the Neolithic was "plenty of time" to adapt to bread, rice, and potatoes.Cordain pronounced several foods (bread, rice, potatoes) to be the cause of a fatal condition in people carrying certain genes. Intrigued, Zuk stood up and asked Cordain why this genetic inability to digest so many common foods had persisted. “Surely it would have been selected out of the population,” she suggested.Cordain, who has a Ph.D in exercise physiology, assured Zuk that human beings had not had time to adapt to foods that only became staples with the advent of agriculture. “It’s only been ten thousand years,” he explained. Zuk’s response: “Plenty of time.” He looked at her blankly, and she repeated: “Plenty of time.” Zuk goes on to write, “we never resolved our disagreement.”
Nevermind that Cordain also offers the same point for refined sugar, vegetable oils, high fructose corn syrup, BPA, and refined salt, all of which I'm sure <sarcasm>have nothing to do with evolution</sarcasm>. (Had they been a significant part of human evolution, we would have evolved to consume them more safely. But hence, they were not significantly; nor were processed bread, rice, and potatoes, to a lesser extent.)
It's a valid question: is the Neolithic "plenty of time" to adapt to new food sources? Unfortunately, the answer is obviously not.
Zuk's central thesis hinges on Neolithic evolution.
This is a great example of Zuk being right about something yet at the same time being wrong about everything. Yes, humans evolved during the Neolithic, as they are evolving now. Yes, they evolved faster than before. But she misinterprets these facts in their entirety.The most persuasive argument Zuk marshals against such views has to do with the potential for relatively rapid evolution, major changes that can appear over a time as short as, or even shorter than, the 10,000 years Cordain scoffed at. There are plenty of examples of this in humans and other species.
She seems to imply that Cordain doesn't believe in Neolithic evolution, or at least that he doesn't believe it's relevant to human health. I'm sure this is untrue, since I've seen Cordain address lactase persistence, a point Zuk brings up herself. And then she goes one step further to accuse "educated individuals" of not believing in Neolithic evolution:
Zuk detects an unspoken, barely formed assumption that humanity essentially stopped evolving in the Stone Age and that our bodies are “stuck” in a state that was perfectly adapted to survive in the paleolithic environment.I don't even know how to address this straw man. I mean, who says that?
Nobody says that.
Yet Zuk is the one with a misconception that "Surely, [bad genes] would have been selected out of the population" since we had "plenty of time" to evolve during the Neolithic. She explains why this is a misconception herself:
“A strong body of evidence,” Zuk writes, “points to many changes in our genome since humans spread across the planet and developed agriculture..."Part of that "strong body of evidence" demonstrates that the vast majority of bad genes in existence today arose during the last 400 generations (1). In one study, 86% of those bad mutations appeared in the last 10,000 years (2). This means that bad genes are not necessarily being selected against, and good genes are not necessarily being selected for. There are so many people reproducing according to such chaotic pressures, we are evolving like crazy.
The assumption Zuk gets wrong is that evolution is the same in the context of civilization as it is in the wild. The truth is that evolutionary pressures change so drastically in the environment of civilization that the very term 'natural selection' is a misnomer, because the way nature select for traits in the wild is not applicable to the environment of civilization. It is the pressures of the civilization itself that are choosing traits, not only "nature" in strict terms. This is the background that explains why the pace of Neolthic evolution increased so rapidly in the first place, something she seems to overlook. I call this evolutionary mechanism 'semi-natural selection' in order to emphasize the sea change in evolutionary pressure.
Zuk brings up some interesting examples, all of which prove, if interpreted correctly, that she is wrong about the significance of Neolithic evolution. The examples are a quickly-evolving cricket, lactase persistence, and early grain cultivation.
First, a fascinating story about crickets:
In one astonishing case, a type of cricket Zuk studied, when transplanted from its original habitat to Hawaii, became almost entirely silent in the course of a mere five years. (A parasitical fly used the insects’ sounds to locate hosts.) This was all the more remarkable because audible leg-rubbing was the crickets’ main way of attracting mates, literally the raison d’etre of male crickets. The Hawaiian crickets constitute “one of the fastest cases of evolution in the wild, taking not hundreds or thousands of generations, but a mere handful,” Zuk writes. Adjusted to human years, that amounts to “only a few centuries.”Crickets are a false analogy to humans (wild vs. civilization). In order to rectify the analogy, we would have to assume that bad genes are selected against in civilization. So people with celiac, for instance, are removed from the gene pool. However, this is not the case, because civilization makes it quite easy for people with celiac to survive and reproduce, sending their genes along into eternity. In a small population in the wild, if food was scarce and wheat was the only option, it's likely that those genes would see extinction. And in "only a few centuries" they would disappear. (This may very well be true to some degree for populations who saw this kind of evolutionary pressure at the turn of the Neolithic. Quite literally, people who could not thrive on grains may have just died out during times of scarcity. So, to some degree, we are partially evolved in that direction, an idea I'll cover later.) Evolution and survival in the wild is mathematical: the greater the pressure, the faster the pace of evolution. Too much pressure, the species goes extinct, as 99.99% of all species have. The crickets in this story probably almost did go extinct due to the pressure to survive, but they made it out of the throes of extinction by evolving rapidly, according to pressure. For humans, these pressures are wholly different in society.
Lactase persistence is another example of a partially formed adaptation that proves nothing. Some people produce lactase into maturity while most people do not. But can't you already see why this point is moot? All humans are evolved to consume milk, as animals have been since the dawn of mammals. It's only a small number of people today who can do it comfortably into maturity with the milk of other animals. There is still a gray area of evidence about whether it's safe for these people, since they still get disease. And it's only a handful of people, so how is that "plenty of time"? And is she really going to argue that 7,000 years is enough time to evolve to drink milk, but 3,400,000 years is not enough for meat???
Early grain cultivation is an interesting point, and I think it's true that we are better suited to more "natural" grains, in evolutionary terms. However, like Miller points out about vegetables, none of these exist today. Grains are genetically modified and processed. While it's true that we have been eating them longer than corn syrup, they are still relatively new to the human diet, offer little in nutritional terms, and are just a bad idea all around.
Miller mocks generalizations about evolution before introducing one of Zuk's own that humans probably ate "whatever they could get." Um, what does that even mean? Doesn't everyone eat what they can get? Is she implying that humans would literally eat whatever they can get? That could be a lot or a little depending on lots of things. Ultimately, this is just another bad generalization. Let me introduce a better one: humans ate food available in the wild. Hence, why they are evolved to those kinds of foods. Isn't that the logic behind why we should choose natural food sources?
And then there's the most obvious fact of all that destroys Zuk's "plenty of time" thesis. If the Neolithic was plenty of time to evolve to a Neolithic lifestyle then why is our society rife with disease, illness, and nearly ubiquitous personal anguish? Is this who we are "stuck being" as Laura Miller suggests? Are we going to be able to consume high fructose corn syrup in a "few centuries"?
Ridiculous.
But another thing Zuk is right about: just because something is new does not mean it is bad. I recall a podcast with Mat Lalonde and Chris Kresser where Lalonde argues, "There are plenty of examples of animals taking up a new food source and thriving." I also recall thinking, how is he measuring that "thriving"? Population growth? Lifespan? Because if population growth and lifespan are indicative of thriving, then agriculture and civilization obviously spur human thriving! I mean, humans do technically 'thrive' on agriculture and civilization, but that doesn't mean you thrive eating pizza and heel-striking treadmills.
Ultimately, I still have no idea where Zuk and Miller are going with all this. We shouldn't eat meat? We shouldn't enjoy nature? We shouldn't pursue healthy sexual relationships? What is she getting at? Is she saying anything of substance at all? I guess I gotta read the book. But I'm not going to.
References
1. Keinan and Clark (2012). Recent explosive human population growth has resulted in an excess of rare genetic variants. Science 336 (6082): 740-743.
2.Fu et al (2012). Analysis of 6,515 exomes reveals the origin of most human protein-coding variants. Nature [ePub ahead of print] Retrieved from http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11690.html
