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April 26, 2005

Slow and diverse food

I suspect most long-time GNXP readers would be surprised to know that over the past few hours I just read a book that sported blurbs from the modern Malthus, Paul Ehrlich, anti-transhumanist author Bill Mckibben and world famous chef Alice Waters. But Gary Nabhan's book, Why Some Like it Hot, intersects with a personal interest of mine, the relationship between biological predispositions and our gastronomic preferences and nutritional "optimum." I have posted before on the genetic factors that shape our experience of taste multiple times (see here, here and here), so readers will find the chapter which is reflected in the title of Nabhan's book covering familiar ground, with talk of PTC, PROP and "supertasters," and an emphasis on the physiological response to capsaicin.

My interest in the topic is shaped by my own life experience. The natal cultural background into which I was born is rather liberal in its use of spices, and in particular in the apportionment of chili pepper. But even among other Bengalis the extremes to which my paternal side used chilis was considered rather exceptional, and living alone, without parental supervision, I have taken it to the "next level," and only the fact that I can not dispense with 2 hours every day writhing in pain due to stomach cramps prevents me from the copious consumption of habañeros. Instead, I settle for a small dispenser of cayenne which serves as a constant flavor companion.

In past I have wondered if this predeliction of mine was partially heritable in the genetic sense, or simply imitation of my father. More precisely, I was curious as to whether there was genetic variation underlying some of the phenotypic variation on this trait, so 6 years ago I undertook to scour some back issues of The American Journal of Human Genetics, and that was where I found the first references to PTC, PROP and the possible correlates of the sensitivity to these chemicals with various natural flavors. I have reviewed much of the literature in detail at the links provided above, so I will simply quote Nabhan, "About 25 to 30 percent of all Mediterranean residents were taste-blind, while only 7 percent of Lapps, 3 percent of the West Africans, and 2 percent of the Navajos sampled were notasters. In Asia, taste blindness varies from 43 percent in India to 7 percent in Japan." I want to both emphasize the the modal frequency of taste blindness in South Asia, as well as the possible tenuous connection between "taste blindness" and insensitivity to chili peppers. As my links above make clear, attempting to scry a proportional relationship between taste blindness and particular cuisine or use of spice can be a sketchy proposition. Nevertheless, I think the data will be firm enough in a few years that we can start decomposing the relationship between genetics and cultural traditions in the domain of food (for the record, I am a PTC non-taster).

But Nabhan's book is far more than about chili peppers. He focuses a great deal on nutrition and its evolutionary background, as well as attempting to offer cost vs. benefit analyses in light of his values. All for the good, but there are a few problems with his narrative. Several times in the text Nabhan declares he is not a "Darwinian." His assertion is grounded in his conception of Darwinian theory as assuming a "slow" and "gradual" evolutionary change, while Nabhan believes that selective sweeps, genetic drift, population isolation and persistent directional selection can alter phenotypic expression and genotypic frequencies on the order of thousands (dozens of generations), even hundreds (a few generations), of years. He notes that his thesis is predicated on microevolution.

Well, I guess it shouldn't surprise us that evolution doesn't make sense to John Q. Public if a man who promotes himself as an "ethnobiologist" and "nutritional ecologist," and admits to taking genetics courses in college, can't really keep things straight (PhD. Arid Lands Resource Sciences, University of Arizona, 1983 M.S. Plant Sciences, University of Arizona, 1978). In The Genetical Theory of Natural Selection the modern day prophet of Darwinism, R.A. Fisher, spent half his book discussing the impact of microevolutionary pressures on human societies exactly on the time scales that Nabhan assumes is not "Darwinian." It seems that Nabhan conflated macroevolution with microevolution, and forgot that the latter is the true heart of Neo-Darwinian theory. I pointed to Fisher's Fundmental Theorem of Natural Selection in an earlier post, and an astute reader suggested that there are serious problems with this model in a multi-locus context. Even disregarding that many of the traits that Nabhan alludes to are single-locus, the empirical "breeder's equation," R = h2*S1 offers one a sense of the rate at which evolution can work. Something like the black death, or perhaps a period of famine, could certainly result in a great deal of selection, and as Nabhan himself states, many populations suffered endemic malaria or frequent drought related die offs, so it is highly plausible that microevolutionary forces are working within conventional Neo-Darwinian models could effect widespread genotypic change. Additionally, though the term never comes up, I can't but help thinking that Nabhan is simply presenting an adaptive landscape narrative (epistasis, geographical isolation, etc.) as formulated by Sewall Wright, as much a Darwianian as Fisher (though perhaps not an ultra-ultra-Darwinian).

Which brings us to the elephant in the room. Human biodiversity. Nabhan might not even come close to the cognitive taboo, but, he is quite clearly arguing for the relevance of functional genomic differences between populations. His examples of the tragedy that occurs when Native Americans become addicted to alcohol, the response of Sardinian males to fava beans and malaria, the changes wrought upon the physique of aboriginal peoples by processed carbohydrates and the ability of Cretans to live on a diet rich in greens and high in fat all underscore that he is focused on difference, sometimes individual, but usually populational. All that said, he does trot out Richard Lewontin's famous 85-15 figure, but promptly skips over on the next page to an approving excerpt of Sally Satel's I Am a Racially Profiling Doctor. Ultimately, Nabhan's book starts to turn into a jeremiad against the Axiom of Uniformity.2 On the one hand Nabhan dismisses with little consideration the contention of Lewontinesque arguments, but he takes a rather large bite out of the Paleo Diet assumption that we can assume an Environment of (Gastronomic) Evolutionary Adaptedness. Here I believe he is on extremely strong ground, the Baldwin Effect has had an immense influence on human beings since the Neolithc Revolution. As Nabhan and others have noted, humans have taken control of the natural world and we now reshape our own environment of selection, so the adult metabolism of lactose is likely a product of human choices in domestication subtly changing selective pressures on the population doing the domesticating. The assumption of fixation of allele frequencies (that is, tendencies are monomorphic) in an EEA in the nutritional realm probably does do a great deal of harm, and I think Nabhan's stridency is probably warranted. Death to the Universal Diet!

Coevolution between culture and genes plays a large role in Nabhan's narrative. Sardinian's relationships with the fava bean and their evolutionary response to endemic malaria is a tight and relatively tidy tale that offers sharp insights on the importance of microevolutionary forces. This was probably the reason that this was the first heavily scientific chapter. The problem, from my vantage point, is when Nabhan begins to move from specific cases to general political-philosophical implications. When a dust jacket declares that the author is a leader in the "Slow Food Movement," you have a good indicator as to the conclusions the author will reach from the data at hand. I can agree with Nabhan that doctors and public health policy makers need to consider the genetic vulnerabilities of Native Americans to alcohol when allocating scarce resources so as to optimize yield. I can also agree with Nabhan some interpersonal confusions about the character of foods can cause a great deal of stress in one's life, I suspect some individuals become offended when I pepper their food (ie; they prepared it), but I also suspect those same individuals would be dousing their dinner with cayenne if they ever had to face the gaping void of blandness that often stares me in the face. But an emphasis on cultural diversity, preservation of indigenous traditions and a precautionary turning back upon genetic and medical advances in favor of the "old ways" seems a bit too far. I am to some extent likely caricaturing Nabhan, but not necessarily painting a false picture of his outlook, which to me resembles Russell Kirk more than J.S. Mill (the old is better than the new, the particular better than the general).

His portrayl of nutritional disaster that befell indigenous peoples of the Americas and Australia thanks to their flash immersion in modernity is spot on in its description. Many isolated populations seem to bloat up and contort their internal catabolism of sugars when they become part of the modern agricultural-industrial distribution system. Nabhan admits that Europeans and other agricultural peoples probably went through selection pressures after the Neolithic revolution so as to be able to more efficiently (or less deleteriously) metabolize grains, and though the experience of indigenous peoples is not analogous (thanks to modern medicine) it is not totally inaccurate to say that they have spanned centuries in generations when it comes to their lifestyle. Instead of "genetic fixes" via gene therapy (he strangely avoids selective abortion, which wouldn't alter the germ line in a direct fashion) or GMOed crops Nabhan councils many of these people return to their traditional foods. It is this drastic prescription where I think he has unmoored himself from science to values. He talks enthusiastically about Australian Aboriginals returning to the hunter-gatherer foraging patterns of their ancestors. It might be a lifestyle they wish to endure for the sake of their health, but would they see a "genetic fix" as such a terrible price to participate in a 9-5 modern world where there simply isn't enough time to go into the bush every day to retrieve wild game, herbs and roots? Nabhan does not seem particularly sympathetic to individual choice, and well he shouldn't be as one of his close friends was a Navajo Indian who died of self-induced alcoholism, but, he also constrains the field of action to the dead past and the sub-optimal present. He doesn't see much hope in a future where reason can "cure" many "ailments" that are the legacy of our genes. Who is the "Panglossian" now? If Nature made it, don't break it. Despite his nostalgia for the "old ways," modern Western medicine has done great things (or does Nabhan only visit a Navajo shaman?). The quality of life that hunter-gatherers have is not all that, judging from the fact that many of them stream into cities to work as menial laborers when they get the chance, disappointing their "defenders" in their relative fickleness and preference for the consumer goods of the global culture. Additionally, this also does not speak to the fact that some of the building blocks that Nabhan uses to construct the edifice of an organic, holistic and functionally adaptive traditional culture are tenuous and scattered. He cautions us toward being too greedy in our need to erect a simple model and redesign nature based upon it, but he engages in the same sin himself, mapping fuzzy and not "proven" science directly on to his values.

I am not here to deny that "Slow Food" and traditional ways have any use, or that people shouldn't be allowed to choose them, but Nabhan seems to assume that there is no way most "indigenous" people would want to live as moderns, and that the predicament they are in is in part an outcome of the choices they make in their own life. He brings up the term "bioculture," and minimizes what clearly seems a Navajo genetic illness related to blood albumin and its response to a particular chemical found in desert plant because it brings life experience to the individual and furthers the cohesion of the tribe. I can just see him lecturing, "some must suffer for the tribe to prosper." This sort of functionalist argument is not something I am particularly sympathetic to in terms of the values I espouse as a post-Enlightenment individualist, we do not today live for society, we live within society. Nabhan has lost the trees in the forest. I suspect in his everyday life Gary Nabhan also lives within society rather than for it (after all, it is a globalist consumer machine), and I wish he were more open to offerring others the same opportunities, and granting that they might not be totally irrational to try their luck with the tool that is modern science. Appeals to "holism," "traditions," and "spirituality" sound to my ear an awful lot like noble savage romanticism. Finally, I would add that though Nabhan tends to focus on populations, as he acknowledges in the near future we will be able to zoom in on the scale of individual genomes. Decisions must be made in the light of the information on hand, and in the age of only sketchy information about individual genomes populationally relevant data is crucial, and so I can grant the importance of tradition mediated through the group in this context, but it seems somewhat superfluous in the looming post-genomic age.

In short, lots of interesting stuff collected in one place (though do a literature search, his interpretation is somewhat sketchy often), but also a bizarre window into how the pro-traditionalist-if-you-are-not-white Left might view issues of human biodiversity.

1 - Response = narrow sense heritability * Differential between total population mean and breeding population mean.

2 - See here for an elucidation of "Major Axioms" espoused by some on this weblog.

Posted by razib at 08:06 PM