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):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.
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.
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):
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.
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.
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.