MARLENE ZUK IS AN EVOLUTIONARY BIOLOGIST at the University of Minnesota. Her last book was a pithily entertaining look at sex on six legs. In her new book, she has jumped from bugs to humans. Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live contains a tiny bit about two-legged sex, quite a bit more about human diet, but mostly it dissects our fantasies about the distant Paleo-past. In particular, it addresses the currently popular notion that if we adopt the lifestyle of our Paleolithic ancestors — whether that means running barefoot, or heaving boulders in one of the nation’s “CrossFit” studios, or eating raw meat still dripping with blood — then we’ll be more in sync with our real natures. As she points out, a growing number of Manhattan urbanites and Silicon Valley types are zealously, indeed quasi-religiously, trying to access their inner “Grok” (lingo, in case you didn’t know, for their Paleo- or cave-selves). But, they’re barking up the wrong tree, and missing the real lessons of evolution, according to Zuk.


Michele Pridmore-Brown: You just wrote Sex on Six Legs, which makes sense in terms of your work on crickets and sexual selection, but now, in this book, you’re busting a cultural myth about our hominid evolutionary past. How are they related?

Marlene Zuk: The two books are more connected than people might think. A lot of my day job — as a biology professor and researcher — got me interested in rapid evolution and how quickly change can happen. Our work on crickets showed that a mutation that alters their wings and makes males unable to chirp spread throughout the population in fewer than 20 generations, remarkably quickly in evolutionary terms. Being unable to chirp protected them from a parasitic fly, so that’s why the mutation was advantageous. I started thinking more about what determines the rate of evolution. Lots of new evidence is suggesting that some traits in people, such as adaptation to high altitude, might also have evolved very quickly. This then made me ultrasensitive to all these mentions in the press and popular literature and even in conversation about how we humans have gotten out of sync with our environments because we evolved as hunter-gatherers in the Paleolithic — some x thousand years ago, say 10,000 to 200,000 years ago. The idea is that, because of modern life, we have developed this awful malaise: we’re out of sync with our real selves and the best way to remedy that is to mimic the diet, exercise, and childrearing practices of way back when.

MPB: In your book, you’re very specific about the form these attempts at mimicry take — for instance, supposed Paleo diets that eschew starch and allow only roots, berries and meat; so-called “CrossFit” exercises that mimic running from lions and heaving boulders, and so on. It seems like you’ve got two things going on: consumers misunderstanding evolution, and then Paleo-fantasies as a kind of secular religion.

MZ: When I was researching this book, I read a lot of stuff on Paleo blogs and websites, and I can tell you I was struck by how deeply invested people are in a particular version of what the past is like. And now I should mention my caveat that I am not writing a diet book. I don’t care what people eat; or rather, I’m not giving advice on what the best diet is. I’m not even saying whether the Paleo diet is good for you. Not my concern. Rather, I’m interested in this use of a vision of the past to base decisions on. So often, you get this response from Paleo aficionados of: “Well I’ve switched to a Paleo diet and my allergies are much better and my sex life is improved,” and so on. That’s fine for them, but if we want to understand which diets are best for people, we need to look at the data.

MPB: I guess you could say our fantasies about the Paleo-past smack of the 18th century French philosopher Jean-Jacques Rousseau’s return-to-nature cult. Did he not promulgate accessing one’s inner “noble savage” as a way of curing the ills of civilization?

MZ: Absolutely. Our Paleo-fantasies play into this whole nostalgia thing. Humans have always looked to the past, even their own childhoods, as a better, more wonderful time, when life was simpler, easier, healthier. Maybe these Paleo fantasies are just an über-manifestation of nostalgia for a lost past. I’d be curious what people in other fields think about the pervasiveness of this idea that we’re mismatched to our environment — and what it would mean to feel well suited to it.

MPB: In your book, you mentioned a 1987 piece by Jared Diamond in Discover entitled “The Worst Mistake in the History of the Human Race.” He’s referring to agriculture, which seems to be framed as a kind of original sin. Did he have a hand in launching this Paleo-craze?

MZ: I haven’t read his current book, but I think his focus is more on what we can learn from foraging tribes. I certainly agree with that. My objection is to the assumption that what we did before — say, pre-agriculture — was healthier, or even ideal, and then, somehow, we got kicked out of the Garden of Eden, and it’s all been downhill. Diamond talks about the ways in which agriculture was bad, and he is right about those costs. Of course, walking upright is bad for us too, at least in some ways, but that ship has sailed. I think a deeper understanding of evolution helps you better understand the futility of pointing to a moment in time as being the perfect one.

MPB: Can you say a bit about how we’ve evolved since the dawn of agriculture, 10–12,000 years ago? And how there’s no going back to some prelapsarian moment, even if there was one, which there wasn’t? We were never happy savages, or even just disease-free.

MZ: Right, there was never a time when our bodies or minds were in perfect sync with the environment. Besides, humans aren’t all alike, and we never were; people have been variable throughout our history. And, yes, it’s clear that human health got worse right after the adoption of agriculture — in part because there were a lot more people around. In other words, if you have a steady food supply, then people have more babies, and then there’s crowding, which means an increase in diseases that you don’t get when there’s separation. And if you are sedentary, diseases like cholera, which are spread through contaminated water, are more likely to occur.

MPB: Getting back to your point about rapid evolution, what are some examples of the ways humans have evolved since agriculture? Besides the lactase gene (for digesting milk), are there other dramatic examples uncovered in recent years by genomic research? In other words, part of your point is that we can’t return because we are already different, so we’d be even more mismatched to the past than we are to the present.

MZ: New genetic tools are allowing scientists to scan the human genome looking for signatures of selection, and they are finding evidence of recent evolution all the time. Depending on our ancestry, we have new genes for resisting disease, for living at high altitudes, and for digesting starch, all abilities that our more distant ancestors lacked.

MPB: You use a nice metaphor of a maloccluded zipper to describe the fit between an organism and his or her environment. We are always, almost by definition, maloccluded, it seems?

MZ: Oh, yeah. It’s not like everything is going to line up. If you’re a real organism, then the fit is only just “good enough.” The Nobel-winning biologist François Jacob famously said that “evolution is a tinkerer, not an engineer.” An engineer says, “I need to solve this problem and I’m going to find the best parts, put them together in the most efficient way possible, with a clear endpoint or finished product in mind” — the finished product being, for instance, a bridge or a computer chip. Evolution doesn’t work like that. Rather, the tinkerer just has stuff lying around in, say, the garage, and this tinkerer can only work with the materials he’s already got. As organisms, we ourselves carry around in our bodies all the materials that evolution can act on, and some of it we’ve had since life began. Noah Shubin’s book Your Inner Fish talks about this: if you look at human anatomy, you can see traces of our evolutionary past. There’s all these parts that don’t work ideally because initially “the tinkerer” was working with a fish skeleton and there’s only so much you can do if you need to breathe air but have gills. You’re always handicapped, or jury-rigged, or sometimes it’s a happy facilitation, but in any case evolution is always tinkering and there’s no endpoint. That’s the other point of my book: that there is no engineer saying, “Oh, we need to get from here to there and then we’ll be done.”

MPB: Getting back to your title: I assume that part of the Paleo-fantasy regarding sex is that we were meant, by fiat of nature, as it were, to be either overtly or covertly promiscuous?

MZ: Well, the myths are variable. There’s also, on the other hand, this myth that we’re meant to be monogamous or to live in idealized Cleaver-like families — and that we’re going to hell because we aren’t. Everybody is interested in this idea that there are certain universals — like raising kids, or parents loving their kids, for instance. But you get on shaky ground when you extrapolate further. The promiscuous label is interesting because people play that one on both sides, depending on their agenda.

MPB: You have an interesting point in your book about human males and adaptability. We’ve heard a lot recently in the news, especially in the The Alantic, about the limits of male adaptability (as compared to females). I was intrigued because you refer to testosterone as in fact a mediator of evolution.

MZ: Yeah, well, this stuff has to happen through some mechanism. It’s like thinking about those parts in the garage, and what’s lying around. If you’ve got testosterone lying around in your garage, then you tinker with it. Testosterone has a lot of different effects. To think about testosterone as this chemical that destines men to be surly, uncommunicative, and violent is missing the point entirely. Selection can act in a lot of different ways, including on testosterone. In many species of male birds, elevated levels mean that they start to sing in the spring, and yet, clearly, it doesn’t have that effect in human males. In other words, testosterone does different things in different organisms, and in the same organism but different contexts. New fathers, for instance, have lower levels of testosterone compared to what they had before the kids were born. And if they sleep with the new baby, they have even lower levels. In other words, there’s a complex dance going between the environment and the body. It’s an ongoing back and forth.

MPB: This seems like an argument for paternity leave.

MZ: Sure, you could say that. I’m not going to say all men will react to infants in this way or that we should institute a policy. Rather, my point is that males with high levels initially may end up with lower levels, depending on their environments. Men can adapt to childrearing — and changes in testosterone levels mediate this adaptation. This idea that they’re destined to want to spread their seed, well, it’s a myth of sorts.

MPB: You mentioned old fathers as a rich source of mutations, which I know is not good at an individual level, even if these mutations do provide raw material for natural selection. I wondered if you might speculate about what effect IVF, contraception, and parental postponement is likely to have in the longer run?

MZ: Whether more raw material and variation will end up resulting in more rapid evolution … I don’t know. One of the most apt quotes I came across in the literature was this: When someone asked: are we still evolving? The answer was the question: are we all having the same number of children? Since the answer to that question is no, we’re evolving and will continue to do so.

MPB: One more question about your book: what’s next or what do you feel that you left out?

MZ: There’s a chapter I almost wrote for the Paleo book, and I ended up not having time because I was moving from California to Minnesota. It was about Paleo-fantasy pets. There’s so much we’re finding out now, about dogs and other domesticated animals. An article just came out about how dogs have amylase genes, which allows them to digest starch. When dogs were domesticated, they must have foraged in the dumps of early humans, and were also able to eat scraps. So, it’s possible that even your dog didn’t eat a Paleo diet. It illustrates the point. The noncarnivorous dogs (with the gene) must have outbred the purely carnivorous ones. So, not only have there been recent genetic changes in us, but also in the organisms we interact with.

MPB: Here’s a writerly question. You run a lab at the University of Minnesota, you pursue research on crickets in Hawaii, you teach and direct graduate students, you go to conferences, you write academic articles — how do you manage to write popular science books as well?

MZ: [Laughs] Sometimes one or the other ball is falling! The writing is fun. I get to interact with people I wouldn’t otherwise interact with. It’s just not enough to live a life where I’m doing science and interacting with scientists. As for method, I write in bits and pieces. I do substantial parts of my books on sabbatical. In general, though, I do try to be pretty disciplined. I have a word goal of 1,000 words a day. So, if I get to a hard part in the middle, I have to keep going to get the 1,000 words. But, it’s never continuous because my life just isn’t like that. When my students who are writing dissertations tell me that they have to have x number of uninterrupted hours, and it has to be in the morning or whatever, well, then I tell them they’re in the wrong line of work.

MPB: What do your colleagues think of your books?

MZ: I don’t want to come across as snarky here, but some my colleagues have this attitude of, “Oh yeah, you write for the general public. I would if I weren’t doing something more important.” And, naturally, they think they could do it really easily! There was always this question of whether, if you do books for the general audience, does this count as scholarly output, or is it more along the lines of outreach, or, say, teaching. I made the case that it was scholarly; in other words, just because it’s not wet lab work — I’m not collecting data and so on — it’s still got scholarly implications, or so I argued.

MPB: For you, which is harder: the pure science or the popular science writing?

MZ: Well, I don’t know. [Long pause.] You have more control with writing, whereas with science you don’t know what’s going to happen. At the same time, not knowing is soothing in a way. You have to wait and let it unfold, and I don’t know if that makes it easier or harder. That’s an interesting question. The difference definitely lies with control. In science, you can exert control in the sense that you can design your experiments, and decide what questions you’re going to ask, but nature’s doing what it’s doing and you can’t control that.