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I am a politically-progressive, ethically-herbivorous anthropoid pursuing a paleontology education in the Los Angeles Basin. I am largely nocturnal, have rarely been photographed, and cannot thrive in captivity.

20 May 2011

Fallback Food Fight: Defintions & Clarifications

I blame myself. It seems that despite my best efforts, the Permavegan and I have been talking past each other. His latest response in our ongoing debate reveals this quite clearly; in the first half of his article, the Permavegan calls me to the carpet about the imprecise use of language:
In the above passage, the Humane Hominid is not using the terms preferred food and fallback food in a manner that is consistent with optimal foraging theory, or with the understanding of fallback foods that emerged during early primatological studies, as I cited from Constantino and Wright (2009) in my contribution to round two:
The fallback food concept appeared relatively early in primatology. It seems to have been introduced by Hladik (1973) who was commenting on chimpanzees’ increased consumption of leaves and stems during periods of low fruit abundance (Tutin et al., 1985). Although the term ‘‘fallback food’’ does not seem to have been widely used at this time, seasonal variation in primate diets quickly became a regular part of primate feeding studies (e.g., Waser, 1975; Chivers, 1977; Fossey and Harcourt, 1977; Hladik, 1977; Wrangham, 1977). These studies made it clear that most primate diets shifted seasonally, even in species living in ‘‘stable’’ tropical forests (Hladik, 1988). In light of optimal foraging theory (MacArthur and Pianka, 1966), researchers also recognized that certain primate foods should be more ‘‘preferred’’ than others. For example, in a study of the feeding behavior of Bornean orangutans, Rodman (1977) discussed the difference between ‘‘preferred’’ and ‘‘less preferred’’ foods and argued that bark was less preferred than fruit because it has a lower energy yield and greater cost of procurement. The combination of these two concepts, dietary seasonality and the prioritization of food resources, led to the understanding that many primates experience a particular time of the year when preferred foods are in short supply and that certain fallback foods can be critical for the survival of these populations (Leighton and Leighton, 1983).
In the case of chimpanzees and Bornean orangutans, the staple food of fruit is defined as the preferred food, and those plant foods which have a lower energy yield, are more costly to procure, or are relied upon during periods of seasonal stress are designated less preferred or fallback foods.  Curiously, the Humane Hominid admits that "fruits, tubers and seeds" were what our hominin ancestors "depended on most of the time for our daily survival," but for some reason he is not comfortable referring to these plant-based foods as preferred foods!
 But, it doesn't stop there! Next, he points out another apparent contradiction on my part:
On the other side of the inversion - that meat is a preferred food in the hominin diet - the Humane Hominid responded to my round two challenge as follows (emphasis added):
This question -- and all four of its sub-questions -- seem to me premised on a single, probably flawed, assumption: that there was ever a time that hominins didn't eat other animals. I am skeptical that any such time ever existed. As far as we can tell, hominins...have always been at least somewhat behaviorally carnivorous.
This rather subdued appeal to peripheral behavioral carnivorism is a completely different assertion than the earlier proposition that plant-based staples were the fallback foods and meat was the preferred food for our line of descent.
To the first part of this implicit charge, I must plead guilty. My definition of "fallback food" was indeed imprecise, leading to the present confusion. So, let's back up a bit.

Floating around unspoken in my mind during our debate thus far has been the definition of fallback food summarized in the paper by Marshall, et. al., to which I had linked in my first installment (emphasis added):
Physical anthropologists use the term ‘‘fallback foods’’ to denote resources of relatively poor nutritional quality that become particularly important dietary components during periods when preferred foods are scarce.
Also, Richard Wrangham's summary of the definition influenced my responses (again, emphasis added):

The term fallback foods refer to foods poor in nutritional value compared to preferred foods and ones that become important in the diet when preferred OR commonly eaten foods are unavailable. Operationally, however, the term is used more broadly. For example, Hadza foragers take more tubers (USOs) when honey, meat, berries, and baobab are less available, yet tubers are eaten in all seasons constituting a significant portion of total diet. In contrast, core diet components for yellow baboon are defined as anything taken in amounts >1%. The concept should prove useful once a consistent definition is accepted by users.
As can be seen by Wrangham's final sentence, as well as a close reading of the Marshall, et. al., paper, anthropologists haven't yet settled on a single precise definition of the term. But they are getting close, and key to both major proposed definitions is the concept of "dietary quality" or "nutritional value," meaning not how healthy a particular food is for a given individual, but which ones are the most calorically-dense; i.e., which foods provide more energy than it takes to acquire them. I neglected to emphasize this point in both of my responses, and so I must ask the Permavegan's and the reader's forgiveness for the confusion this caused.

That a food is eaten as a staple, or seasonally, does not by itself make it a preferred food. Nor need fallback foods be eaten rarely; after all, I prefer vegan chocolate chip cookies by the bag-full, but I rarely eat them. Whether a food is considered fallback or preferred depends on "dietary quality" as well as, if not more than, frequency of consumption.

Fallback foods are food sources of low energy pay-off that a species uses to "get by" during lean times. They are often (though not always) eaten more frequently than preferred foods, or common foods with higher nutrient densities, and for this reason sometimes appear to influence a species' evolution.

Once we understand that the key issue here is nutritional quality, we can see that there's actually no contradiction my two seemingly incongruous comments. Primates will go to great lengths to procure a preferred food, though some are lucky enough to have their preferred foods available to them for long periods of time (I could, for instance, go to Trader Joe's right now and have a good chance of finding a bag of vegan chocolate chip cookies; thus, for minimal effort, I can acquire a tasty food that's high in calories). They will also fall back on less-preferred foods when the more-preferred ones are scarce (maybe Trader Joe's is out of vegan cookies, so I go back home and make a whole-food smoothie instead). The foods they adopt during these scarce times might actually be calorie-dense themselves (like fruits and tubers), but if they're less calorie-dense than the more-preferred foods, they'd be classified as fallbacks.

Admittedly, I find it all a bit arbitrary, and have complaints that it seems to simply assume (without testing) that meat was a better energy deal for hominins than calorie-dense plant foods were. But here, paleontologists can only work with the evidence they have; it's impossible to test how efficient, say, Homo ergaster was at digesting meat compared to plants. The best we can do is look at current human characteristics in comparison to those of other extant primates, and extrapolate logically backward into the fossil record, using the scientific method to look for clues in the morphology of our ancestors and the rock record of their enviornment. I'll deal with that issue later, though. Right now, we should focus on getting our definitions straight.

When I echo the standard anthropologist line that meat is properly classified as a preferred food for hominins -- or at least for the genus Homo -- I am not necessarily saying that meat was commonly eaten, or easier to acquire than plant foods (though again, much depends on which hominin species one wishes to emphasize). I am simply thinking of the caloric pay-off that meat -- particularly cooked meat -- granted to early humans, for which they demonstrated a growing preference over evolutionary time, affecting both their dental morphology and behavior, culminating in the great megafaunal extinctions of the late Pleistocene. In short, as Homo's ancestors and then Homo themselves became better at tool-use and hunting, meat-acquisition no longer violated the parameters optimal foraging theory because they could spend progressively less energy in the effort, and meat thus became increasingly preferred. That's the standard paleontological view of human evolution, and one that I think is pretty much in accord with the fossil evidence, subject to the caveats I offered in my last post on this topic.

So, to re-iterate, I have been assuming that the term fallback food refers to food of low nutritional quality that an animal relies on at times when preferred foods are scarce. Preferred foods are foods of high nutritional quality that may or may not be eaten regularly. So, when the Permavegan pauses to ask me directly:
when we are talking just about the plant-based portion of the chimp diet, isn't it most logical to describe the staple fruits and greens as the preferred foods, and relegate the pith, bark, and seeds to the fallback food category - especially to the extent the latter foods are consumed during lean, dry seasons, when the former foods are scarce or unavailable?
I would answer "yes, absolutely. That, however, does not mean that the rarely-consumed meat in chimp diets is also a fallback food. Whether food is classed as fallback or preferred depends on the food's nutritional quality as well as the frequency of its consumption."

All In The Family?
Before we close, however, another terminological question looms. The Permavegan notes:
I am confident it is just a slip of the tongue in the Humane Hominid's exposition, but my understanding is that chimps, bonobos, and humans are indeed all hominins. 
This confusion stems from a proposal by a team at Wayne State University School of Medicine in Detroit, Michigan, to re-classify chimps as members of genus Homo based on genetic similarity. Wikipedia treats this proposal as though it's been accepted, including chimps and bonobos in the taxon, but in fact, it is still being debated. Linnaean classification is traditionally based on morphological rather than genetic characters, and as of this writing, chimps and bonobos have not been incorporated into the tribe Hominini* (though I would not be opposed to this proposed change).

So, to the second half of the Permavegan's implicit charge, I plead not guilty, and instead blame the system.

Much of this common misunderstanding has to do with the use of Latin suffixes in taxonomy. While it is true that humans, chimps, bonobos and gorillas are grouped together in the subfamily Homininae, they are not all part of the tribe Hominini. The Homininae are divided into the tribes of Gorillini (gorillas), Hominini (humans and their fossil ancestors) and Panini (chimps and bonobos and their fossil ancestors). Roughly speaking, the word "hominin" now refers to what used to be called "hominid"; that is, H. sapiens and their extinct fossil ancestors, including all of the genera Homo and Australopithecus, along with Paranthropus, Ardipithecus, Kenyathropus, and the various other ancient forms.

I hope this helps clear some of the cobwebs out of our discussion, especially since the Permavegan has had much to say over the last week about other topics touched on in my last response, such as vegan bias in this debate, whether veganism is an exclusively modern ethical stance, and whether our ancestors' diet has moral implications for us today. Rather than devote blog space to each of these questions here, I will attempt to address them in the comments section of the Permavegan's blog and save Paleoveganology for the main spine of our discussion.

So, keep checking his site, and be on the look out here for further installments. I won't move on to a discussion of chimps vs. humans until we have sorted out this terminological issue.

*This is why I prefer Citizendium, where expert review carries some proper weight, over Wikipedia, and always check it first when looking for explanatory links.


  1. It is not easy, Humane Hominid, to subject our thoughts to the scrutiny of an opponent in an extended public debate. I very much appreciate your diplomacy and your spirited marshalling of arguments and evidence.

    The latest post you reference is an excellent clarification of your position. I appreciate your rapid and constructive response; it really helps to pinpoint the crux of our definitional disagreement. I believe there are genuine contradictions in your proposed definitions, and that these contradictions are in turn based on a misplaced emphasis on "nutritional quality" in the excerpts of Wrangham and Marshall et al that you cite. In my next post on this topic, I will further explain my position by elaborating on the discussion of Darwin's finches in the touchstone paper by Constantino and Wright.

    I am not yet convinced that a reductionist emphasis on "nutritional quality" - further reduced to caloric density - is the central concept in a discussion about preferred and fallback foods. Nor am I comfortable to so quickly conflate cultural concepts of "preferred" and "fallback" foods with ecological and evolutionary meanings that may be completely opposite the cultural conception, as I submit is the case with Hadza tuber consumption. The starchy tuber is undoubtedly a preferred food for Homo, though a late-comer relative to fruit and greens, while meat is one of our most costly and risky fallback foods, in terms of morphological evolution via natural selection, no matter what cultural preferences have evolved since the emergence of our species. I understand this is a controversial assertion, but I don't believe my hypothesis is that easy to rule out. At any rate, I think we might as well take our discussion of these concepts all the way back to square one - to the ecological and evolutionary importance of fallback foods as evidenced in the case of a Darwin finch - and build back up to chimps, following the lead of Constantino and Wright. It may be easier to grasp the distinction between preferred and fallback foods without making anthropomorphic errors if we begin with an even more clear-cut case in finch morphology.

    The Wikipedia article from which I drew very much treated Pan as a genus distinct from Homo, but your point is well taken that the best working definition of a hominin, for our purposes, may not be the one advanced by scientists who refuse to look at both genetic and morphological evidence in a balanced fashion. We might as well keep DNA analysis out of the courtroom. Fortunately, we are independent bloggers - and you are anonymous - so we can employ the Wikipedia definition of hominin with the appropriate caveats and without fear of academic censure if that is the definition we think the science best supports.

    I very much welcome any thoughts you have on the various side-issue posts I have peeled away from the main trunk of our dialogue, but neither do I mind if we let them go for now in order to focus our energy on a shared understanding of preferred foods and fallback foods. Feel free to proceed as time allows.

    Tech Note: I tried to post much of this comment on your blog last night, but that earlier version is either awaiting moderation, filtered as spam, or didn't save. Feel free to toss it if you find it. For some reason, I can't comment on Blogger recently using my Google account. Something is up with Blogger or my account, so I am commenting here using name/url.

  2. Jonathan,

    Somehow, both your comments got flagged as spam by Blogger, but I have resurrected them, unsure of which one you'd prefer to have appear here.

    In a short while, I'll be posting a link to a paper by Marshall and Wrangham that contains much more rigorous definitions of "fallback" and "preferred" than I used in this post, though they are along similar lines.

    As for the hominind/hominin question, I actually don't think the science supports including chimps as the latter, though as I said, I am not automatically opposed to the idea and am willing to be convinced. I'm working on a post about the significant anatomical and morphological differences between chimps and humans that make using chimps as an analogue for Homo problematic at best. But, I was planning on waiting til we sort this fallback v. preferred terminological issue out.

    I should note here that the definitions I'm using are not my proposed definitions, but the definitions I have been taught. To some extant, I am playing devil's advocate in supporting them uncritically, since my bias leans towards you. But even so, I don't think they are completely arbitrary or anthropomorphic, either.

    If you prefer one of your comments over the other, let me know and I will delete the other one.

  3. Thanks for the update and the offer, Humane Hominid; go ahead and delete my first comment, per the tech note in the second.

    I have had a chance to read your most recent post citing the definitions of fallback foods and preferred foods by Marshall and Wrangham. It is a very useful contribution in terms of explaining and justifying your line of thought, but in my view these new definitions are just as problematic as the ones cited above. This is not to say the definitions are "completely arbitrary and anthropomorphic," but in my view there is an anthropomorphic error in the above. I will elaborate on this in an upcoming post.

    I do not mind treating "hominin" as exclusive of Pan if there are still good reasons to maintain the division after the genetic arguments have been duly considered. In your last post you said, "Hominins have always eaten other animals, to some degree or another. Modern chimps (who are hominids, not hominins, but still closely enough related to us that we can make reasonable inferences) are known to prefer meat whenever it's available to them or whenever they can catch prey; thus, we can reasonably assume that this preference is ancestral to Homo, as well."

    Curiously, you now seem inclined to argue exactly the reverse, i.e., to minimize the "reasonable inferences" we might draw about hominin fallback foods from our study of the chimp diet. I am not sure why you are reversing direction.

    I very much appreciate your point that you are to some extent uncritically supporting the definitions you have been taught because it fits within the role of devil's advocate I have asked you play - not because these are the definitions to which you are necessarily the most logically or ethically committed. In the same way, I am being less cautious and more spontaneous than I would in a scientific publication, because it fits the spirit of the dialogue. Thank you for your willingness to play the harder role!

    I am not yet sure it is accurate, however, to say that your bias leans toward me. Just because we are both vegan, we are not necessarily biased in the same intellectual and philosophical ways. Although we are both genuinely committed to a vegan lifestyle, our systems of justification are quite different. This makes sense in part because we are two different people with two different intellectual histories, but it also makes sense because (as I contend) our veganism is based as much on a psychobiological reality of empathy as it is on various abstract conclusions we derive from scientific speculation.

  4. Re: chimps --

    I actually haven't changed position at all! The key word in my comment was "ancestral," which in the study of evolution is distinguished from "derived" or "unique." My position is that omnivory is ancestral to primates in general, and thus for both chimps and humans, but that degrees of frugivory or carnivory are derived traits. As I will show in my chimp post, chimps are adapted to a greater degree of frugivory and humans to a greater capacity for carnivory.

  5. So at this point in our clarification of terms, there is not really a need for you to bring chimp-human differences into the picture. Whether you think chimps are more adapted to frugivory or less adapted to carnivory than humans is irrelevant, because we do not yet agree on the classification of meat as a preferred food or a fallback food in the chimp diet alone!

    You say that whether meat should be put in a fallback or preferred category of the chimp diet depends on its nutritional quality, the frequency with which it is consumed, and the energy return. What nutritional evidence do you cite that meat is a food of higher nutritional quality for chimps than fruits and greens? How do you contradict my claim of distinct fallback seasonality in chimp consumption of meat? And what evidence do you have that meat affords chimps a better energy return than staple fruits and greens?

    I addressed the frequency issue in my chimp diet post, and I have suggested that energy return cannot be separated from either morphology or ecological niche in my comments. With respect to nutrition, I think you face a heavy challenge on a great many fronts, not the least of which is chimp Vitamin C dependency.

  6. I agree there isn't a need to bring chimp-human differences into the discussion, yet. Except, that the differences between them may, in fact, be both determinative of and influenced by which foods are fallback and which are preferred for each species. And anyway, I'm only trying to prepare for the eventuality that however we resolved the preferred/fallback issue WRT to chimps, you'd cite chimp behavior and diet as a meaningful analog for early hominins; you may not end up doing that, in which case, it won't be necessary (though I may do it in any case, because it's darned interesting on its own merits).

    In terms of specific nutritional information on chimps, I admit I have none at this point. I just know that meat, in general, is classified as a high-quality food among anthropologists because of its caloric density and ability to make an organism feel sated, thus freeing them up to do other things than forage. It may well turn out I was mistaken in asserting that meat is considered a preferred food for chimps, specifically; but the fact that they actively seek it out rather than just eat it opportunistically has generally led to the conclusion (so I've been taught, though my none of my teachers thus far have been primate specialists) that it's a preferred food rather than a fallback one. Chimps can digest cooked chicken and raw boned beef with no digestive problems, at least in controlled amounts, and in captivity appear to relish them both.

    This gets at your questions in paragraph three, above, as well as your suggestion that energy return can't be separated from morphology or ecological niche. Under the rubric of the definitions offered by Marshall & Wrangham (which are the ones I had intended to use all along, and which I think are largely the same as what I wrote in this post, though more precise), staple fruits, greens and meat would be preferred foods, while the bark/pith/seeds category would be fallback. Again, the fact that meat is consumed seasonally by chimps does not, by itself, make it a fallback food... although it might. Its apparent role in sexual selection argues for it being preferred, not fallback. We'd have to look at whether chimps who hunt animals overselect them relative to their abundance in the local habitat to figure out if it should be considered a preferred or fallback food.

    WRT to chimp vitamin C deficiency, I don't think there is contradiction. That chimps have a nutritional dependency on fruit does not logically preclude meat from being a preferred food for them; the preferred status of a food isn't tied to the specific nutrient needs of a given species, but to its role in sating their hunger in the quickest, easiest way possible for the longest amount of time. Nutrient/calorie dense foods do this better than nutrient/calorie poor ones do.

    Before closing, let me add that I'm working out my thought process on this issue in the open, in writing, so it's likely my position will shift; also, that my blog takes a back-seat to my actual daily studies, so my work here isn't always as rigorous as it could be (right now, I'm study for finals and gearing up for a summer internship!). I apologize for the confusion this seems to entail. I will endeavor towards more precision for the sake of this debate.