evolution

I guess I’m kind of late to the party on reviewing this book, but I actually haven’t noticed a lot of reviews of it, which is surprising given the amount of buzz the articles about it generated. I also suspect some reviewers didn’t actually read it, since they seemed abnormally fixated on defending their paleo diet, when the book only has two out of ten chapters devoted solely to diet and covers many other topics.

Like Marlene Zuk, I am also quite critical of some of the movements that use (and mis-use) evolutionary logic like the paleo diet. So I wanted to like this book.

It has its good moments, but is overall in need of a good editor. It could be much shorter. And much less meandering.

Much of the skepticism is directly towards the frequently-inane postings on online discussion boards, which I a have the misfortune of being very familiar with having moderated one of the most popular until I rage-quit in annoyance.

While a lot of people get dumb advice on internet discussion boards, do they really define these movements? While they are fun strawmen to take down easily, most people don’t take such posts seriously. What they take seriously is the often scientific-sounding books written by various gurus, often with many letters, legitimate and not, preceding and following their names. While she mentions them, it’s only in passing. Her “paleofantasy” seems to consist mainly of cacophony of crowd-sourced internet discussion.

Not to say you won’t learn anything from this book, but it hardly challenges the status quo, which makes the hysteric reactions of many against it and the author seem all the more ridiculous. A lot of it reminds me of the excellent The Beak of The Finch or The 10,000 Year Explosion. She covers many methods that evolutionary biologists use to understand evolution, why they matter, and common misconceptions about them.

But if only people were talking about evolution when they were talking about the paleo diet. Talk about actual evolutionary biology and you might be met by some of the silent crickets that Zuk studies. Only 54% of paleo dieters in a recent survey accept evolution as a fact.

But it’s beyond that the increasing specialization in of academia becomes a limitation. Zuk specializes in the evolution of crickets, which yes, does have surprisingly broad applicability, but she spends a long time on that and other similar research that I think a skeptic would find irrelevant and unconvincing. I read The Beak of the Finch, which discusses this type of research in length, in high school, and it didn't stop me from adopting the paleo diet narrative. I think the most common problems with the “paleo” worldview come from anthropology. For example, misinterpretations of isotopic studies, coprolite fossils, and paleopathological surveys are used very often to justify “paleo” diets.

On the cultural anthropology side of things, people often seem very confused by terms like “hunter-gatherer” or “forager.” Rather than elucidating the complexity of historical humans lifestyles, the book muddles this further in parts. If you were confused about this before, you’ll stay confused, and a clarification would improve her arguments anyway. For example, whether or not the Yanomani (of the Chagnon controversy) are relevant to revealing some aspect of hunter-gatherer “human nature” is pretty questionable considering that while they do forage and hunt for some of their food, they are horticulturalists, a lifestyle that probably not much older than agriculture. Same goes for Jared Diamonds extrapolations from the horticulturalists of Papua New Guinea in The World Before Yesterday.

This is also common in Paleo diet books– authors like Cordain cite starch-cultivating horticulturalists like The Kitavans when convenient, while recommending a diet that bears little resemblance to theirs. I noticed recently that paleo guru Art De Vany’s blog header has a picture of some imposingly muscular tribal warriors. The site doesn’t seem to say anything about them, but I knew they are Asaro “mudmen” of Papua New Guinea, who are horticulturalists and grow many crops that De Vany would view as unhealthy. It is a shame to see them exploited to promote his diet and as of late, extensive advertising of his own supplements.

Fuled by sweet potatoes, sugary fruit, and peanuts they grew in their forest gardens

If you are confused, for almost all of the paleolithic humans were nomadic hunter-gatherers with primitive weapons. There are really no people today who practice this lifestyle. If agriculture is a drop in the bucket of human history from a relative perspective, even the innovations of the Middle and Upper Paleolithic, are similar in relative timescale. These innovations included better weapons- the atlatl and later the bow and arrow, which would have affected hunting significantly. They also included the culinarily important pottery and grease-processing (smashing up bones to make a fat and protein rich broth). I made this crappy timeline that gives a vague idea of some of these innovations in human history. What time do you choose as the optimum? 

Our ancestors’ diets clearly changed dramatically and repeatedly over the last tens, not to mention hundreds, of thousands of years, even before the advent of agriculture.

Even the few representatives of nomadic hunter-gatherers that exist on the planet use these relatively modern technologies, like the Hadza’s bows.

I don’t think these groups of people are irrelevant to health discussions though, if anything, these people show that diversity of lifeways in which our species has been able to thrive, a thread that seems constant no matter the time. And every lifeway has involved trade-offs. For example, while rheumatoid arthritis, which is common in industrialized first world cultures these days, seems to have been rare in foraging cultures, osteoarthritis seems to have been more common.

And in the end while it’s fascinating to think about how so much we are familiar with is “new” in their scale of geologic time, Zuk rightly points that evolution works faster than many might imagine.

I think the sections on lactase tolerance, which talk about in how many places and ways humans acquired this trait, are fascinating. But left also many unanswered questions that show just how far we have to go to understanding human evolution.

Interestingly, about half of the Hadza people of Tanzania were found to have the lactase persistence gene—a hefty proportion, given that they are hunter-gatherers, not herders. Why did the Hadza evolve a trait they don’t use? Tishkoff and coworkers speculate that the gene might be useful in a different context. The same enzyme that enables the splitting of the lactose molecule is also used to break down phlorizin, a bitter compound in some of the native plants of Tanzania. Could the lactase persistence gene also help with digestion of other substances? No one knows for sure, but the idea certainly bears further investigation.

But while she mentions a little elephant in the room, which is our microbiota. Of “our” cells, bacterial cells outnumber “human” cells ten to one. And they have had a lot more generations to evolve than “we” have.

Microbiologist Jeffrey Gordon says, “The gut microbial community can be viewed as a metabolic organ—an organ within an organ . . . It’s like bringing a set of utensils to a dinner party that the host does not have.” 44 As our diets change, so does our internal menagerie, which in turn allows us to eat more and different kinds of foods. The caveman wouldn’t just find our modern cuisine foreign; the microbes inside of us, were he able to see them, would be at least as strange. 

I like that she takes on the common narrative of “people were really healthy until they became farmers and then they shrunk and had bad teeth etc.” The reality is while some of the earliest agrarian cultures did seem to suffer compared to their predecessors, it wasn’t all about the food and people by and large recovered. Besides, if we were going to pick diets based on bone and teeth health, we might as well pick the pastoralists like Masaai, who tend to be much much much taller than any hunter-gatherers.

Then a funny thing happened on the way from the preagricultural Mediterranean to the giant farms of today: people, at least some of them, got healthier, presumably as we adapted to the new way of life and food became more evenly distributed. The collection of skeletons from Egypt also shows that by 4,000 years ago, height had returned to its preagricultural levels, and only 20 percent of the population had telltale signs of poor nutrition in their teeth. Those trying to make the point that agriculture is bad for our bodies generally use skeletal material from immediately after the shift to farming as evidence, but a more long-term view is starting to tell a different story. 

Many paleo diet books present our species as that of fragile creatures rather than what we really are, which is the consummate omnivore resilient and adaptable enough to thrive on a large range of foods. A curious being, that was travelled far and wide and tasted many things, rather than being defined by fear and a narrow food exceptionalism. I’ve even seen people, some of them fairly well-known bloggers, on Twitter and Facebook discussing buying an island where “paleo dieters” could be free from “non-foods” like grains and the people that eat them. It’s not as bad as blog posts from paleo dieters travelling in foreign countries who talk about how difficult it is to explain their special food to the local people. Traditional cultures are venerated, maybe even exploited, unless they don’t fit the paleo narrative.

The question is whether the various forms of the paleo diet really do replicate what our ancestors ate.

Unfortunately Paleofantasy focuses on this absurd strawman of dietary replication and only begins to scratch the surface of neurotic botany of many paleo writings. Books that fret about whether or not “nightshades” grew in Paleolithic Savanna Africa and their plant chemicals, while blithely consuming other classes of similarly alien plants with other potentially problematic chemicals. Because that’s what plants are– bundles of chemicals that can be friend or foe depending on amounts and contexts.

 The skeptics she cites aren’t much better than the internet commenters representing paleo. They include the Ethnographic Atlas, a survey of modern populations, that she claims puts to “rest the notion of our carnivorous ancestors.” Or the U.S. News & World Report’s rating of diets.

It doesn’t take an evolutionary biologist to understand what the paleo diet has become, especially in alliance with the low-carb diet promoters, industrial supplement companies, or the standard dieting-culture food fear mongerers. It functions not as an attempt to use evolutionary biology to understand the human diet, but has become a social engineering scam to sell mediocre books, processed powders, and other crap. It was only about evolution in the beginning, mostly it’s just a diet in caveman clothing now.

Paleofantasy has just come along for the ride. It’s not going to convince very many people caught in the scam. It’s just going to make those who haven’t feel smug. At least it might teach a few people about evolutionary biology.

And I liked the section about attachment parenting, which is surprisingly rational about the matter, a welcome break from so many writings that either are almost religious about it or decry it as some kind of upper middle class fad.

The evolutionary psychology section is also not as critical as I thought it would be from the reactions of those are are enamoured with the subject.

There is a long section on barefoot running, which talks about how some paleo diet proponents like Art De Vany think we did not evolve for long-distance running and other evolutionary fitness advocates like anthropologist Dan Lieberman think is it a critical part of our evolutionary heritage. I think this highlights the fact that the past is so hazy that it’s pretty easy to use it to support a whole host of contradictory arguments.

It’s a shame Zuk tilted at internet idiot windmills and not at the far more sophisticated arguments that are dressed up as science. I sometimes wonder if publishing companies don’t want authors to criticize other authors. They have 199 Paleo Fried Chicken Recipes (I made that up, but it’s not that far out) and other book-like products to push before people get bored.

These books are also relentlessly shallow shadows of some of the earliest texts in the genre of using the deep past to better understand how we should live. Recently I was struck by the similarity in the cover of The Primal Connection: Follow Your Genetic Blueprint to Health and Happiness and the late Paul Shepard’s Coming Home to the Pleistocene.

I read Coming Home to the Pleistocene when I was twenty. While I certainly don’t agree with everything in it, it is beautifully-written and thought-provoking. It challenged the way I thought about the world. Paul was not afraid to espouse controversial ideas, unlike the books from the diet industry that turn the original ideas into drivelling Flintstones platitudes in order to appeal to everyone. I suspect people will still be reading Shepard in a decade when all the paleo publishing bubble books languish in the bargain bin.

Zuk says in closing that “I am all for examining human health and behavior in an evolutionary context, and part of that context requires understanding the environment in which we evolved.” I agree with this. I think evolution is important and will continue to improve our understanding of our world. And I eagerly await a book that more fervently challenges common misconceptions about it.  

 I've seen the idea that there are no primates adapted to eating grains, but actually there is a primate that is better adapted to such a diet than any others. It's the gelada (Theropithecus gelada), which lives only in the Ethopian highland grasslands. The gelada is the only living member of genus the Theropithecus. Several larger gelada species once roamed most of Africa, including the terrifying giant gelada, which was around the size of a modern gorilla. But now there is just one, which is also one of the few primates that endures sub-freezing temperatures, which occur at night in the highlands. 

The gelada is also quite interesting because it is a grazer, relying mainly on grass. It prefers the seeds of the grass, which are yes, grains. 

This is unusual for primates. Some, like anthropologist Clifford Jolly, have speculated that hominids once occupied a similar niche. But this was mostly in the 1970s and this model for understanding human origins has fallen out of favor. Some extinct lines on the family tree (Paranthropus for example) were thought to have eaten similar diets based on low-quality plants, but more recent evidence has cast doubt on this theory. Frederick Szalay's reply to Jolly's paper in 1975 noted that as climate changed, hominids and the ancestors of gelada may have both moved into the grasslands.

But as hominids rose, the Theropithecus genus fell, backed into a corner by adapatations to eating grass that seem incomplete and inefficient. Geladas require very high quality grass, not the low quality grass that started to dominate as Africa warmed up again.

The gelada and related baboon line seems to have a longer history of consuming starchier foods than the frugivorous lines that led to us. One piece of evidence is that baboons and geladas have higher salivary amylase expression than even humans cultures adapted to high starch diets. 

Unfortunately, it seems that particular this genus adapted itself into a corner, with adaptations not good enough to compete with animals like zebras for the increasingly low-quality grasses in the warmer low-altitude grasslands, but complete enough that grass-eating was probably obligatory. Primates with an ability to consume a more flexible diet, like our ancestors, rose, while most Theropithecus died out.  

Why such big scary teeth on a grass eater? Big scary teeth are about more than food, they are also the hallmark of territorial species where males fight for domination of harems of females as seen in this video of a gelada male battle.

While geladas were busy chomping on grass pretty much all day, there is some good evidence our ancestors were scavenging large animal carcasses, developing a taste for meat and perhaps spurring us to eventually hunt and develop tools to acquire more protein this way. The geladas went the route of low-quality protein, while the hominids went the route of high-quality protein, protein that may have allowed us to develop large brains and free up time from foraging to develop advanced culture. Geladas probably got less intelligent due to their overspecialization, while hominids and their closely related baboon cousins used their intelligence and flexibility to thrive in a variety of habitats. 

Later, our niches would cross again as humans developed our own way to extract energy more efficiently from grass through technology and selective breeding for grain yields. Not surprisingly, geladas are thrilled to munch on such high quality grasses. While they are not a big as their ancestors, they are still a formidable pest ,as this Human Planet video shows:

Researching geladas might give us valuable clues to understanding our own species. For example, looking at the adaptations geladas have to eating their diet could tell us something about the kind of challenges a grain-eating primate faces and we could compare them to our own physiology to see how well we have adapted or not adapted to similar dietary challenges. However, geladas eat wild uncooked grasses, whereas humans have an entire culture of complex preparation that alters the structure and composition of our food significantly through grinding, fermenting, cooking, and other technology. 

 In my last post, I wrote about how it's impossible for epigenetic changes from very cold environments 3-4 billion years ago to have been conserved. Somehow people thought I was accusing Dr. Kruse of making up cold-adapted monkey ancestors or something. 

No, I realize he doesn't mention cold-adapted monkeys, but he also doesn't stick to bacteria living in sad cold slurries either. He also mentions ancient mammals. Dr. Kruse also has an interesting belief that all mammals “evolved in the polar environments on earth.” 

I can't find any evidence that early eutherian mammals evolved in such an environment or even a later candidate for a polar eutherian that could be a possible ancestor. They discovered the earliest known (so far) eutherian fossil last year in China, Juramaia sinensis, in a Late Jurassic formation. The climate in the area at the time was relatively warm and dry. Juramaia sinensis' teeth suggests it was an insectivore. Many other early mammal fossils have been found in Asia, but as we know, mammals went on to colonize a variety of environments and climates. 

Dr. Kruse says "mammals were ideally adapted for hibernation too, until they got too smart for their own genes sake.” It is indeed true that Juramaia sinensis and other early eutherians did hibernate. Mevolutionary biologists now consider the origin of biological changes distinct to hibernation behaviors to have originated even before the evolution of class mammalia and are displayed even in reptiles who live in very warm environments.

Why did most mammals stop hibernating then? As the excellent paper The Evolution of Endothermy and Its Diversity in Mammals and Birds says “ energy-optimization-related selection pressures, often dictated by the energetic costs of reproduction, apparently favored abandonment of the capacity for short- or long-term torpors." In most primates, it seems this abandonment was characterized by a species with a large brain and increased adaptability to a variety of foods and climates.

That's too bad, because hibernation (or even torpor, a less extreme form) would be very useful for things like organ transplantations, surgery recoveries, or long space flights. In the future, if we figure out how to do it, being able to trigger hibernation would be incredibly useful. Unforunately, the exact way to trigger hibernation is not currently known, though there are many promising candidates. Dr. Kruse however believes that the stimuli is already known: “the stimulus for hibernation in eutherian mammals and their descendants are tied to high dietary carbohydrate intake (proven fact already in science and not controversial).” If only it were that easy. A search of the scientific literature found no papers that posited that carbohydrate consumption triggers hibernation, though it is established that carbohydrate metabolism undergoes changes before and after hibernation. Scientists who propose triggering hibernation believe it would probably involve injection of chemicals produced by hibernating animals. This would be possible because many of the genes related to hibernation are still present in primates, not because we hibernate, but because they have other functions. We'd also have to figure out how to prevent brain damage, which has been a major challenge to such research since humans appear to suffer memory loss from brain changes normal to hibernating mammals.

Evolution is efficient and while genes that had interesting past uses (wouldn't it be cool if we could "reawaken" gills or the ability to lay eggs??) are often conserved in our genome, they are often expressed in radically different ways. It seems the areas that once encoded for gills, for example, are now related to the bones in the ear. As for those that don't seem to be in use now, as geneticist Paul Szauter says:

If genes are not expressed in the human genome, they do not survive intact over evolutionary time, because they accumulate mutations in the absence of selection. If there were squid genes in the human genome that could be "activated," it is likely that the accumulated mutations would result in a truncated gene product (3 of the 64 codons are "stop") with many changes in its  sequence.
 

Dr. Kruse believes that humans, like all mammals, are optimized for hibernation and that remnants of mammalian hibernation are activated in humans based on certain times of the day: "It appears 12-3 AM are the critical hours at night are where the remnants of mammalian hibernation lies for our species". This is a far cry from the current state on literature related to hibernation. The idea that remnants of hibernation occur in humans at night also goes against the definition of hibernation. An excellent paper authored by another McEwen, Dr. Bruce McEwen, has a great concise definition "Hibernation is a highly regulated physiological response to adverse environmental conditions characterized by hypothermia and drastic reductions of metabolic rate"

Re-definition and special unique definitions of terms is another of Melia’s characteristics of bad books: “ The texts of these books all continue in the same excited first-person voice. They often introduce vague, undefined or invented terms.” A good example of this is in Dr. Kruse’s PaleoFX talk, where he references “ geothermal circadian cycles.” It sounds scientific, but there are no known circadian cycles that are tied to Earth’s internal heat* and it appears Dr. Kruse invented the concept since it is found nowhere else. It is a particularly deceptive practice, made easier by the fact that many of the terms that are often mis-used by these authors, such as the species concept or even hibernation, are the subject of some academic contention. But while academics might be arguing about whether or not bears are “true hibernators,” we can be assured that no one is considering that humans are hibernating every night because that doesn’t even fit into the realm of contention or the fringes of what is considered hibernation.

The only known primate that hibernates is Cheirogaleus medius, member of suborder Strepsirrhini, which diverged from the evolutionary line that led to humans over 70 million years ago. They also store a lot of fat beforehand, so I don't know if I'd like to hibernate like them anyway. I don't think I'd look so good and I probably wouldn't get much work done.

Even if it were conserved, Dr. Kruse makes the mistake of tying hibernation to extreme cold: “Cold environments are found as mammals hibernate in normal circadian biology…….this completely reverses IR in mammals and wakes them up when conditions are better for life.” Dr. Kruse’s cold therapy involves exposure to freezing temperatures, because he thinks that is linked to hibernation in humans. Kruses asks his readers if maybe diabetes has “become thought of as a neolithic disease in humans because we we have simultaneously lost the ability to hibernate because we evolved the ability to control our environment completely?” However, there are many animals that hibernate without exposure to very cold temperatures and biologists are still debating whether or not relative cold is even needed to trigger hibernation at all. For example, the only hibernating primate, the aforementioned Cheirogaleus medius, hibernates at 30 degree celsius (86 F). And if humans had lost the ability to hibernate because we control our environment, we would find the ability in related primates who do not control their environments. But we do not. The northernmost living non-human primate, Macaca fuscata, does not show any evidence of hibernation or even torpor, even those that do not visit hot springs. Interestingly, their winter diet does include digging for roots.

Why do so few primates hibernate? Around the equator, where primates evolved, seasons operate quite differently than they do in the arctic and other regions far from the equator. Because the environments and climates of Africa are so diverse, with many micro-climates in certain regions, most primates closely related to humans have evolved to be able to adapt to scarcity regardless of Earth’s axis tilt through the reliance on “fall back foods.” Possibly because of this evolutionary strategy, there is no particular dietary pattern that consistently characterizes the seasons for primates as an order or even within species.

Even in non-primates that live in the north, a very small percentage hibernate. For example, some squirrels hibernate, some don't. Those that don't often will cache food and eat it later. Some humans are known to raid rodent caches for carbohydrates. This contrasts with Dr. Kruse’s idea of seasonal biological changes being triggered by changing to carbohydrates or one season being devoid of carbohydrates: “it appears that dietary carbohydrates, which are only present in long light cycles in the summer in cold places, induce mammals to add PUFA’s to our cells to become fluid so we can function as we hibernate.”

According to Kruse, since carbohydrate consumption is tied to hibernation in cold environments, since we don’t really hibernate now (except sort-of, at night according to Kruse), carbohydrates might not be safe to consume: “Since we no longer hibernate……..maybe you need to consider how you eat carbohydrates within the circadian controls? Maybe what you thought was safe………really is not?” The implication is that carbohydrate consumption is only “safe” for mammals in the context of nature’s “design” for hibernation. In terms of our evolutionary line, that makes little sense. The vast majority of primate species consume diets of mainly carbohydrate, with two main digestive strategies. The evidence is that ancestors of modern hominins relied on a mainly-carbohydrate diet until somewhat recently.

If Dr. Kruse’s line of reasoning is true, most primates are living out of balance with nature and have been for millions of years. Some of his followers have said that this only applies if you live in the north since there are somehow some circadian controls only in the North that are tied to carbohydrates (zero evidence provided), but then the mice and squirrels who are eating stored or underground roots are violating natures law. And the idea that if you put an individual primate in the north that it will change its underlying biology to fit the north's light cycles does not have any evidence behind it (and in fact the fact that individual humans don't adapt particularly well to northern light cycles is perhaps behind the etiology of many modern illnesses).

As I will write in my next post, some human populations (and possibly other hominin lines) have genetic adaptations to more polar light cycles, but these are recent adaptations and are not shared by all humans. And one unique thing is that humans that inhabit cold regions have a raised metabolic rate during the coldest season, not a lowered one characteristic of torpor or hibernation, which suggests adaptations more similar to those found in wolves rather than ground squirrels**. Also, I must also discuss longevity being derived rather than ancestral. But I'll leave that to the next post. 

 * Geothermal according to the OED is “ 1. Geol. Relating to or resulting from the internal heat of the earth; (of a locality or region) having hot springs, geysers, fumaroles, etc., heated by underlying magma.””

** are non-hibernating squirrels naughty "nature's law" breakers? Particularly if they are eating stored carbohydrates?

 I usually don't like to watch people speak about stuff. Maybe that's why I almost never went to lectures in college. I prefer to read things. As Data from Star Trek might say, I find it to be the most efficient form of assimilating information. So you can watch my talk on Vimeo thanks to AHS, but if you read much faster (or you are hearing impaired), you can read the transcript below, which was donated by Averbach Transcription, which is run by a paleo enthusiast and you should consider hiring him if you need a transcript:

"Clues from the colon: How this organ illuminates our digestive evolution and microniche" by Melissa McEwen from Ancestry on Vimeo.

Dynamic Evolution and The Gut

  [applause] So, hi everyone. I was at Mat Lalonde's talk this morning, and I was thinking, "How am I going to introduce myself, what are my credentials?" And I don’t really have any. I have a degree in agriculture and I study anthropology currently at Columbia University, but I'm not in the Ph.D. program.
But I have had the pleasure to study with Professor Ralph Holloway, who's a really excellent physical anthropologist, and he inspired a lot of this presentation. And I have a website, it's called huntgatherlove.com, and you can visit it, and I have also a lot of the stuff from this presentation is there, and a lot of the references to the papers, if you want to read the original ones.

And yeah, I'm not a core scientist, but my boyfriend Chris is, and I try to study, you know, remind myself that chemistry and biology are really important even in anthropology, and I think a good physical anthropologist tries to really incorporate that into their studies.

What is so special about the human gut? Why do we care about it? Why don't we just eat like this nice ape in this picture on the left and just eat some healthy, high-fiber diet, which is low in fat? Just eat like a salad, because everyone knows that salad is really really healthy.

Well, the problem is we are not like gorillas; we're great apes, we have a shared history with gorillas, but we have our own unique niche. And I think when I'm reading a lot of the literature on evolutionary health, I'm seeing these different viewpoints. One I'm going to call statics, and it has an emphasis on what has been conserved from our evolutionary past from some time period, often which is defined somewhat arbitrarily.

And it also focuses on primate relatives such as gorillas. You know, we're great apes, they're great apes, we should eat like them maybe. And I think of course they have very interesting lessons, but I'm going to emphasize more the dynamic view of evolution, the emphasis on unique adaptations that humans have to their own niche, and our continuing evolution even now.

We're evolving as we speak.

So the static viewpoint is that the ancient human diet of some timespan, you know, Precambrian, Upper Paleolithic, was the optimal human diet. And there was a great deal of emphasis on the fossil record. Professor Holloway always likes to say, "When you look at the fossil record, sample size equals two, because there's not that many fossils from certain periods."

You know, we have part of a cranium and that's it of some periods. So it's pretty hard to abstract from the fossil record. And also emphasize related species that we share a common ancestor with. And a lot of times some of this research comes to the conclusion that a high-fiber diet consisting primarily of plants is optimal, and that everybody, every human being should be able to eat this way and be healthy.

There's a lot of Paleolithic Diet papers, but why not the Cambrian Diet? I mean that was a really long timespan, it was 52 million years versus like two and a half, and these creatures look perfectly healthy to me, and they seem way healthier than I am.

Here's a quote from Stephen Jay Gould that, I was a fan of Stephen Jay Gould for a long time, and I still admire him, but I don't agree with this quote, that, "There's been no biological change in humans for the past 40,000 or 50,000 years. Everything we call culture or civilization we built with the same body and brain."
And I thought Stephen Jay Gould was just this nice guy who talked about dinosaurs, but actually Professor Holloway told me that he has some questionable stuff in his research, and that idea that humans haven't changed for a long time is one of those. Another one is that he denies modern human variation quite strongly.
He has this idea that we're mostly the same, which in some ways is true; in some ways it's not true. And I think it denies the fact that we can gain a lot from looking at continuing evolution. And the dynamic view, which I'm going to talk more about, is humans are unique among the great apes, and recent human evolution has led to important changes, especially in digestion.

And besides our own genetics, we have the bacterial microbiome, and our evolution in that has been even more rapid, because bacteria have many more generations, they reproduce faster than we do. And there's high variation among modern humans, particularly with a growing population and introduction into new environments.

So there's probably high variability in [their optimal diet]. And a book that's been a big influence to me is "10,000-Year Explosion" by Gregory Cochrane and Henry Harpending, and it's, "How Civilization Accelerated Human Evolution." And it has pretty convincing evidence that human evolution not only didn't stop 10,000 years ago at the end of the Paleolithic; it's continued to accelerate greater and greater because of all this new environments and greater populations, and also the changes in culture and technology that have happened since then, which have been very rapid.

And in dynamism we have these four keystones I like to think about. One of them is our unique anatomy. Another one is our unique cultural behaviors. Another is our unique bacterial microbiome, which isn't shared with any other primate, and each person has a unique one. But also just in general a very high variability among humans.

And a lot of this is relatively unexplored because it's very controversial. It's hard to get funding. I've met people who do studies on human variability who can't publish them because they're so controversial.

And especially very important in unique cultural behaviors is a shift towards exogenous food processing. So in humans, in our evolutionary past, we processed food inside of ourselves, but in modern humans and in our evolution towards modern humans we have a shift towards processing food outside the body with cooking and grinding and soaking and all these other processes.

So when we're thinking about human evolution, we have to think of—this is an estimate of cells in the human body, and that there's maybe 10 trillion human cells and 100 trillion bacterial cells. And these bacteria are evolving faster than we are. And they're very very important.

They process nutrients, they produce nutrients, they fight off infections, are an important part of our immune system. They have a role in nearly every disease, even diseases you might not even expect, such as heart disease. There's a new paper that shows that metabolites produced by certain gut bacteria that some people have and some people don't have, in response to certain foods, can produce things that are implicated in heart disease.

And also, behavior. I mean, we can't do many of these studies in humans because they're unethical, but in fruit flies if you change the gut bacteria, you can change their sexual orientation. And you can understand why we can't do that experiment with humans; that wouldn't be good.

So there's several factors with these bacteria, and we have to think about interspecific competition—competition between different species, which is driving a lot of this evolution, intra-specific competition—so within even one species, you have tons of strains that are very different, and they're competing with each other, often in one person.

You can have several strains of one bacteria within you at one time. The host function, our own unique anatomy and genetics; our host fitness, which is quite important nowadays, now that a lot of people aren't as healthy as they once were. Particularly in the gut, there's a lot of people with dysfunctional gut permeability, which really affects the bacterial population.

You have food ingested by the host, and you have the metabolites themselves in microbiota, which is tons of different chemicals and fatty acids. And quite important for humans but not unique to humans is culture and technology. These can affect the gut microbiota too.

And there's a bunch of papers that are quite interesting that have more of a static view, and static's this view that we're going to look at other great apes and see what we should eat today. And I think a lot of this research is very admirable, but I think sometimes they come to conclusions that don't make sense in the light of our own unique anatomy.

One of them is Nutritional characteristics of wild primate foods: do the diets of our closest living relatives have lessons for us by talented primatologist Katharine Milton. Then you have this paper, "The Western Lowland Gorilla Diet, are there implications for health of humans. "

And here's a sample sentence from a paper like this, this paper is called "Case Closed: Diverculitis, Epidemiology and Fiber." It says, "The western lowland gorilla, whose diet may approximate a Paleolithic human diet, has an estimated intake of nearly 60% of its calories through the colon," and the second part of this sentence really puts a question mark on the first part:

You can see that this is quite interesting about gorillas. You know, they eat a diet very high in fiber, and it's all plants, pretty much, and they're getting a lot of carbohydrates in the diet, ingesting in their mouth. But then their colon, the bacteria in the colon is this giant bio-reactor. It's turning this carbohydrate, this fiber, this otherwise indigestible fiber into something called short-chain fatty acids.

And short-chain fatty acids are providing over 60% of calories for the gorilla. So the gorilla is eating a high-fat diet, actually; it's just not eating the fat directly. It's turning the carbohydrates that it's eating into fat, fatty acids.

And humans are quite different from other great apes. Here's a famous paper called "The Expensive-Tissue Hypothesis" by Aiello and Wheeler. You can see they did some linear regressions that looked at, based on other primates that we have data for, what should human organ weights look like?

And here's the expected human organ weights, and here's the observed. And what is different? Look how big our brain is and how small our gut is. But even within our gut, there's reorganization, and the reorganization, the driver of this is this food quality. And when I talk about food quality, I'm not talking about [Hardee's] versus Whole Foods; I'm talking about caloric density.

And with this high caloric density, there's less need for this processing equipment that's internal, these internal organs. And so energy is freed up for other organs, such as the brain, in this expensive-tissue hypothesis.

In this gut-brain tradeoff, you have higher diet quality, increased energy availability, and so larger brain. The small gut with the higher diet quality also frees up energy; larger brain. And more complex foraging behaviors, which keep enable… It's driving like a feedback cycle. You know, the more energy we're getting for our brain, the better—the bigger our brain is and the smaller our gut can get.

And you can see that the organization of the gut too, versus other primates—you have all these great apes here, and you have humans here, and look at the human small intestine; look how much bigger that is compared to the other great apes. And the colon is so much smaller. And you can see this in this chart from the Beyond Veg site, which is a great site.

You can see the chimpanzee has a quite long, well-developed colon. The orangutan does as well. But look at the human colon—it's very under-developed and small compared to these other apes. And we're not sure when this change happened in our evolutionary history. It's not like you can find frozen Paleolithic apes very easily.
But we do have this gut—in the post-cranial anatomy you have some indicators that might correspond to a smaller gut or a larger gut. And here is a chimpanzee here, a modern human here, and Australopithecus afarensis, living around maybe 2-3 million years ago, perhaps one of our ancestors.

And you can see this funnel shape in the ribcage, and a large pelvis, which could accommodate a bigger gut. And humans have this defined waist, which we also find very attractive in humans, and a smaller pelvis. And here's some of these apes stripped down, where you can see this giant gut in the gorilla, and the chimpanzee has a pretty bit gut, and an orangutan does.

Humans and gibbons do not. Gibbons are frugivores, so they eat a higher-quality diet than even the more leafy, kind of sticks and stuff that these other apes eat. And here's a human waist—very small compared to the other great apes, except for the gibbon.

And so in humans, how much do we get from short-chain fatty acids? How much do we get from the colon? The colon's smaller. And the human current maximum estimate is maybe nine percent from short-chain fatty acids. So if we go and eat a gorilla diet, we're not going to get as much out of it as the gorilla does.

We'll probably die if we just eat leaves because we can't turn it into short-chain fatty acids with the efficiency that a gorilla does. We don't have the equipment. But I must add a caveat to that. Most of these studies have been done in Westerners, and there's this new hypothesis floating around in papers, this idea that Westerners are the weirdest people in the world—and we are.

Our culture is totally different from most other cultures, and very unique in the history of the world. And so when we're taking data from Westerners, we have to be cautious, and we need more data from other cultures. Because as I say, humans have high variability. Maybe there are people who can get more short-chain fatty acids from fiber than the average Westerner.

And there's very few papers on this, but I found one from South Africa, and they look at autopsies of humans, and they found that some humans have different-shaped colons than other humans, and divided them up into three different kind of morphological types. Here is a short pelvic sigmoid colon, the so-called "classic type", and the long, narrow type.

And different people had different colons. And certain people, like Africans were more likely to have this colon type, and Indians and whites were more likely to have this smaller colon type. And whether or not this has implications for digestion, I don't know. And I think we really need to explore this, because if this colon is so much bigger, what kind of implications does this have?

Can this person get more energy from short-chain fatty acids? Is this person better adapted to a high-fiber diet? And you can see why this sort of research is controversial, because it also has data about different races. But it's very interesting to me. A lot of papers on this subject are not published in English journals at all; you have to read like Czech or something, so it's hard to track down. But it is out there.

What about the evidence that we see in some papers on the Paleolithic Diet, that Paleolithic humans ate 150 grams of fiber a day? I don't know anyone who eats that much fiber, and there's no known modern human culture that eats that much fiber. And most of those estimates are based on [coprolites], and the method for estimating that is quite questionable to me.

We also have to consider the cultural context. There are some good coprolites from hunter-gatherers in the Pecos Basin. But when you look at those coprolites
and the skulls they're associated with, not all Paleolithic or Stone Age or foraging humans are healthy. The Pecos Basin hunter-gatherers have high amounts of tooth decay.

And some anthropologists who study these skeletons say that these are caused by [tooth wear], but this Ota tribesman, he has extensive tooth wear, which is purposeful in this culture. They wear the teeth down to make them look like that, because it's considered beautiful, and they don't have high rates of tooth decay.

If you look at the Pecos Basin skulls, you'll find that they have really high rates of tooth decay. We need to look at whether or not there's impairment of calcium and vitamin D metabolism, and there's a lot of studies that show that really high-fiber diets can impair these. And unfortunately, some of these studies have come about because in places where the macrobiotic diet is popular—the macrobiotic diet, it idolizes high-fiber, particularly brown rice—and in England, in some communities that eat this macrobiotic diet, they're seeing a return of a disease that is associated with developing countries, which is rickets.

And it's infants on macrobiotic diets that have this. And I think there's an upper limit to fiber consumption that's way below some of these so-called Paleolithic accidents. But there's data you can see in some older papers, in particular data from modern hunter-gatherers, foraging people, like this bushman or the Hanza, and they see that these people eat a very high-fiber diet.

But if you look at the later papers, you really have to look at those because they realized that their method for measuring fiber was incorrect. And you can see, this is a very interesting thing. Here's from one of the papers where they're regretting that it was incorrect. And this is inedible material recovered after these Hanza tribe members were eating wild tubers.

They were sending, when they were doing the original fiber assay, they just sent the wild tubers to the lab and they were like, "Estimate the fiber of this," but as you can see here, these people don't eat all the fiber; they're chewing these tubers and spitting out this part of it. So just like you don't eat the tops of your bell peppers, I hope, or the peels of your bananas—although I did meet a raw vegan who was eating banana peels, [laughs]

So cultural evolution is important, and culture isn't even uniquely human. You can see this primate here, this chimpanzee, it's hard to see, but he's taking a leaf and chewing it, and then putting it in this tree that has a hole filled with water and then pulling it out and chewing on it again, and he's doing that to get water.
Humans have even more elaborate techniques. And one of these, of course, is cooking. And we don't know how old cooking is. I mean, you can ask every different anthropologist and they'll give you a different answer. But here we have sago palm starch processing—sego palm is, you know, they're eating a tree. It's not very edible.

Once you cook it, you pound it, and it's quite delicious. I mean it's bland, but it's good to eat; it provides starch for these people, which is very valuable to them. But we also should think about how is food being changed by cooking? It's increasing the food quality, it's increasing the amount of calories you can get from each amount of food.

But it's also really changing some of the nature, the chemical nature of the fibers. Different types of fiber feed different bacteria different ways. So that's very important. And you can look at markers for this. Here's a different kind of culture that a lot of people don’t think about—literal culture, cultured foods.
Fermented foods are universal in nearly every culture. And fermentation increases the bioavailability of protein and several micronutrients. It preserves food. It is a source of short-chain fatty acids. Perhaps it provides us with essential bacteria. Sadly, some fermented foods are in danger of dying out.

And here's an interesting chart—it's comparing the colonic fermentation, this inner fermentation, with exogenous fermentation in fermented foods. And fermented foods can play many of the same roles as colonic fermentation. And perhaps in our evolution as we're shifting towards eating more fermented foods, this was replacing, this exogenous processing was replacing some of the role of colonic fermentation and cooking provides all kinds of different micro-substrates, short chain fatty acids, bacteria, all kinds of metabolites, which also colonic bacteria provide…

They both modulate the system, actually, and there are studies that show fermented food has all kinds of strange effects that you wouldn't expect if it didn't have all these different weird bacteria in it and stuff—to help people lose weight and the way that non-cultured milk would, yogurt is very interesting.

And in terms of metabolites, here's a really interesting one: Butyric acid. It is produced by fiber. Research has focused on just the bulking properties of the fiber. So a lot of early people who wrote about fiber, they were going to Africa and seeing that a lot of different people who ate a very high-fiber diet didn't have the digestive diseases that Americans have.

And they were saying, "No, because it's because fiber is a bulking agent and it increases transit time, keeps toxins from spending a lot of time in the body." But after they were studying more, they found that there were people in Africa who didn't have these digestive disorders who weren't eating a lot of fiber. But what they were eating were other fermentable carbohydrates.

And so now research has shifted away from just fiber as bulking agent, and into seeing fiber more as food for bacteria, whether bad or good. Unfortunately, a lot of research in this area has focused more on fiber being a universal good, when actually it can also feed pathogenic bacteria.

And butyric acid is an interesting byproduct of some of these bacteria. People with colitis, Crohn's Disease, have low amounts of this butyric acid, and butyric acid is very important for modulating inflammation and all kinds of other processes too. They fed these mice the same diet, and the ones that had butyrate didn't gain weight, and the ones that did, that were fed butyrate gained weight. So, pretty interesting.

But you know, when you're thinking of fiber, often your doctors tell you eat more fiber, but different fiber has different effects. And now that we're thinking of fiber more as food for bacteria, you don't need to just think about fiber. And scientists are looking at more of these like resistant starch, for example, and other different complex polysaccharides and carbohydrates. You can see some types of resistant starch are produced by cooking.

Like if you cook potatoes and you leave them in the fridge, then that's resistant starch, and it's very good at producing butyrate. Some of these other fibers aren't so good at making butyrate. A lot of these fibers, a lot of doctors recommend, for example, wheat bran, and that's not even very good at increasing butyrate.
And I'm very sad that there's not a lot of research that is using a lot of these fibers that traditional foraging or horticultural societies eating. A lot of research uses synthetic fibers that's never been eaten before. And they're interesting, but I'd like to see more research on natural fibers.

But also, as humans have developed culture, we have exogenous butyric acid. A lot of people don't know this, but butyric is in the dairy fats and some of the fat under the skin of some animals, particularly cows, goats, sheep. There's a little in elephants too. And there's some in some fermented foods.

Like this is Ogi, it's a pretty delicious fermented food, although it's an acquired taste a bit. But it has some butyric acid. Most Western fermented foods don't have butyric acid because Westerners don't like the taste. If you have tasted skunked beer, you know the taste and you know why we don't like it.

So, it's incrappy traditional foods, you know, foods we don't really like from around the world. But there is one food that you will eat that has butyric acid, and that is butter. The butter is delicious and it has butyric acid. But we don't know whether or not this butyric acid has the same effect as butyric acid produced by colonic fermentation, there's not a lot of research on it.

This presentation's more about hunting hypotheses than presenting research. I'd love to see research on this; maybe I'll do it when I enroll in a program.
But also, not only do humans have all these differences from primates in terms of anatomy and our culture; we have different microbiomes in the gut. And this is a really great study because it looked at the gut biota of wild primates. Most of the other studies have been primates in labs. And you can see, even among these chimpanzees here, these chimpanzees are, some of them are quite geographically isolated from each other.

They have very different branches in the microbiota. They have different gut bacteria. Humans are here. But you can see, we need more data, especially since a lot of these unique cultures are dying out. We should try to collect gut bacteria from them before that, because, so we can get a real accurate reflection of human biodiversity.

And if you think about gut bacteria, it's very complicated because gut bacteria interact with each other, they interact with the metabolites of each other. You have all kinds of diversity among people. Like some people are methane excreters, and some people are not methane excreters. And scientists aren't sure why that is—if that's something that people acquire at a very young age, or if it's something that can be changed.

Methane excreters are quite unfortunate because when they have this bacteria, when it excretes methane, it smells quite bad. So if you're a smelly person, it's probably because you're a methane excreter. But there's just so many questions about why some people are like this and why some people aren't.

And there's so many different sources of gut variation: Cooking and food prep techniques, microbes in food, types of fiber in food, total fiber consumption. Most of us get most of our gut bacteria actually from our mothers, and when we're born, going through the birth canal, we're colonized.

But a lot of us didn't go through the birth canal. I was born by C-section, and C-section babies have different gut microbiota than non-C-section babies, and what is the impact of this? There's some preliminary evidence that C-section babies are more susceptible to certain digestive disorders.

Antibiotic use:antibiotics, if you take them, they can affect your gut microbiota for years. And there's some interactions with genes too. The real question is how plastic is our gut? How much can we change? As adults right now, if we eat differently now, can we really change our gut? Big question.

Here's a really interesting study. This is children in Burkina Faso; this is children in the EU. You can see, you have all these different species, and they differ between these two populations, in different amounts and different species. There are species here that you don't see here. It's interesting because they followed these children when they were breastfeeding, and they had kind of the same gut bacteria when they were breastfeeding.

But when they started eating solid food, their gut bacteria really differentiated. When does this plasticity end? Is it when a child eats its first food? Is that going to really affect the future of that microbiota? Can an adult do this? We suspect they're already there, but in smaller amounts when the infant was breastfeeding.
And then when the solid food was eaten, did it really differentiate based on the food or because of the population seeds planted at birth? We really need to do these studies while different cultures exist because all our multinational corporations are expanding into the developing world, and soon everybody's going to eat the same crappy diet, pretty much, and we won't have this diversity.

And here's the traditional diet of Burkina Faso, a lot of really high-fiber fermented grains. And the environment is very dry. Also, an interesting thing about gut bacteria: Genetic engineering's very controversial, but bacteria have been genetically engineering stuff for ages; it's called horizontal transfer.
A very interesting study looked at Japanese gut bacteria, and they found that some Japanese gut bacteria had species, they had some genes that the gut bacteria had taken from bacteria that live on seaweed, and these bacteria used to digest carbohydrates in seaweed. So these gut bacteria were able to steal these genes and digest these seaweed carbohydrates.

And only Japanese individuals have them, and even breastfed infants have them. So they've probably been in this population for a while. But it really brings it to highlight that our co-evolution with plants, how long have we been doing this? How many genes do we have that are from plant bacteria, for example?
What about the future? Now that we're genetically engineering plants, are we going to acquire some of that bacteria?

And we can use gut bacteria to track human migraation such as h. pylori. H. pylori's considered a pest in the United States because it's associated with some cancers, but actually in Africa, the African strain is not as pathogenic, it's not associated with these things. So these strains are diverse, and you can use their DNA, changes in the DNA to track h. pylori and human colonization of the world.

H. pylori's been with us for 100,000 years, they think. And right now, and most of us don't have it anymore because we tried to eradicate it. What is that doing to us? Did it have positive effects on us that now we've gotten rid of it? There's a lot of variation with it. And also h. pylori has—there's a lot of epigenetic switches that it turns on and off in response to diet.

And a lot of Westerners who do have h. pylori have two strains: They have the non-pathogenic strain and the pathogenic strain. And it's possible that diet can effect an overgrowth in this pathogenic strain. And perhaps the Western diet is taking this h. pylori and turning it into a monster.
But you know, when I'm looking at these different studies, what I said before about Westerners being weird, you really have to question what is normal. There's a hypothesis in anthropology that humans got their first meat and their first high-quality food from scavenging carcasses. It's controversial, though, because most of us don't have the equipment to process rotten meat, although I have met people in the Paleolithic community that are eating rotten meat, and they say they feel fine.

So, you know, that really begs the question if it's normal. And stomach acid, they is genetic variation in stomach acid, but also it's affected by h. pylori—different kinds of h. pylori can affect stomach acid in different ways. Your diet can affect stomach acid. Inflammation. Actually, we associate gastric cancers with the developed world, but actually there are certain types of cancer that are more common in developing nations, such as squamous cell carcinoma, and this is very common in Africa communities that just adopted corn as a staple crop.

And the theory is that, you know, this corn, this omega-6 excess in the diet increases prostaglandin E-2 and it increases inflammation, and that decreases the acidity of the stomach, and leads to heartburn, which is not treated in these developing nations, and then that leads to cancer. There's also an issue I realized studying carrion scavenging, that humans have high transit time variation.

You can feed two people the exact same diet and it'll go through their stomach in different times. And transit time, if you eat carrion, you want a high transit time, and that just varies between humans. An interesting [disease] that I found out about is called [pig bel], and it's people who are in Papua, New Guinea, many who are cultural foraging people, and they eat mainly a very low-protein diet.

They eat primarily tubers, like sweet potatoes and yams. And occasionally they get a pig, and they're very excited about this pig. So they eat it all really quickly. And they get this thing called clostridial necrotizing enteritis. And if I ate this meat, I wouldn't get this, but because they don't eat meat very much, they have low amounts of protease in their gut, so they can't destroy the toxins made by this and can't digest this meat properly.

And it kills some children in these cultures. So, you know, what you eat can affect the different enzymes in your gut too.
And also, the also case of this in a Western individual was a vegetarian who was living in Samoa, and they ate some fish because they were training for a marathon, and they got this disease.

So the point of my talk is that humans are truly unique, and we're not really sure how we got this way, so I'm hunting hypotheses. And within our population diversity is waiting to be discovered. And I'm really worried about loss of biodiversity in cultural adaptations, and what the implications for this are when we're trying to study and trying to flesh out our human history.

When we don't have very much biodiversity to work with, it'll be harder, I think.

And you know, I think the key is balance. I very much admire some of these models that are looking towards the past, and looking at our primate relatives. But also I'm really excited about plant adaptations, new technology and new mutations in human and microbiota DNA.

I think we have to look at both of these things when we're looking at, you know, looking for the best diet for humans. But it also, you know, we often wonder—I have an uncle who's been a vegan for a long time and he's very healthy, and he says, "I've been a vegan for 30 years," and I was a vegan for only a short time and I felt awful.

And we're related to each other, but there's probably some difference in our microbiota or our genes that make him better adapted to this diet than I was. So it gives a new viewpoint on why do some people do better on one diet or another?

So I'd like to thank Ralph Holloway, Chris Masterjohn, Stephan Guyenet and John Speth. They've really helped out. So thank you.
[applause]
Male Voice: So you would say that your main point is that the diversity of humans is under-appreciated and the difference between people is under-appreciated? Is that fair?
Melissa: Yeah. That people are very different from each other, and will thrive on different diets.

Male Voice: I was struck by a thing you said about most of the gut bacteria comes from your mother when you're born. I was wondering what the implications are for celiac, whether that can spread celiac disease.
Melissa: Yeah. I think a lot of celiac research has focused maybe too much on our own genome, what we share, that there's genes that make us susceptible to celiac. But there's also probably gut bacteria that make us susceptible to celiac, and genes within our gut bacteria. So I think that'll be a future avenue of research in the future.
Male Voice: I was wondering about [unintelligible] research on doctor [unintelligible] work? He looked at the microbiota and found that people have different communities, three communities of microbiota.
Melissa: Oh yeah, I saw that. But they're not sure what the implications of that are. They couldn't connect it with anything, like obesity or any diseases yet. But it's very interesting. They found that some people have very specific—that they divide Westerners, at least, into three specific groups of dominant bacterias. And it was fascinating, but I'm really excited to see what that doctor comes up with.
[applause]