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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.

28 May 2011

Fallback Food Fight: Of Course, The Experts Say It Better

I knew it was out there somewhere. A couple of years ago, I read a paper by Richard Wrangham and "some other dude" (as I called him after I forgot his name) that laid out fairly rigorous definitions of fallback food and preferred food. It was that paper that informed my position in this debate with the Permavegan, but I hadn't been able to remember where I'd read it.

Well, while doing research on Google Scholar for an upcoming post on chimp vs. human evolution, I found the long-lost paper in question, Evolutionary Consequences of Fallback Foods. And it's worth quoting extensively, for clarity's sake (emphasis added):
Although FBFs are not always operationally defined, the term most often refers to items assumed to be of relatively poor nutritional quality and high abundance, eaten particularly during periods when preferred foods are scarce (Hanya 2004; Knott 2005; Laden and Wrangham 2005; Lambert et al. 2004; Ungar 2004, Yamakoshi 2004a).
Accordingly, one can operationally define FBFs as foods whose use is negatively correlated with the availability of preferred foods (cf. Altmann 1998; Conklin-Brittain et al. 1998; Doran et al. 2002). Two points about the concept should be stressed. First, the definition of fallback foods implies a distinction between preference and importance. Whereas preference is a matter of dietary choice, importance is a measure of dietary composition. For example, the importance of a particular item might refer to its use as a proportion of total caloric intake, or the percentage of total feeding time spent eating it. Although preferred foods are in some circumstances important, they need not be, as illustrated in Table I. Similarly, high importance of an item in the diet does not necessarily imply positive selectivity or high preference. Fallback foods tend to be foods of low preference but of high importance seasonally.
This is the distinction I was driving at in my "Definitions & Clarifications" post. I.e., the fact that a primate regularly eats a large amount of a given food does not necessarily make that food "preferred," nor does infrequency of consumption make a given food "fallback."

So, if a fallback food is "negatively correlated with the availability of preferred food," what then is a preferred food according to Marshall & Wrangham?
We advocate a classic definition: preferred items are overselected. In other words, preferred food items are selected disproportionately often relative to their abundance within the population’s habitat (Leighton 1993; Manly et al. 2002). Thus, preference is defined as the relationship between 2 parameters: availability and usage. Neither rarity nor frequent utilization is alone sufficient to characterize a food as preferred.
Fallback foods influence adaptations for processing (i.e., mastication, digestion, etc.) and preferred foods influence adaptations for harvesting (i.e., locomotion, tool use, etc.).

On the question of whether meat was a "fallback food of last resort," as the Permavegan contends, much will depend on which stage of hominin evolution we choose to focus on. To me, it is clear that by the time Homo arrives on the scene, meat is a preferred food, often over-selected (at the end of the Pleistocene, to great ecological detriment) as our intelligence and technological capacities made us more efficient hunters.

For the australopiths, the picture is a bit murkier. There is some evidence that they ate meat, but whether it served as a preferred food or a fallback food for them is open to debate, which I guess is what this little tete-a-tete between vegans is all about.

But that gives us the additional problem of trying to decide which australopiths or other pre-Homo species we decide to claim is ancestral -- and thus, most relevant -- to Homo. And I don't think we're going to figure that one out any time soon.

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.

14 May 2011

What, No Bugs?! -- Paleo-Diet Paper Reveals Glaring Blind Spot

I don't pay as much attention to the "paleo diet" blogosphere as I probably should, seeing as how my humble blog now appears on their Paleobuzz site... so it took me a while to come across this paper written by several head honchos of the paleo diet movement. From what I can tell, it hasn't been discussed too much on any of the paleo-diet blogs.

Now maybe that's because because I don't pay much attention to them and simply haven't noticed. Or maybe it's because the authors undermine an important tenet of the "paleo-diet's" paleofantastical view of the Stone Age:
Secondly, in contrast to common belief, hunting probably played a less dominant role from a nutritional point of view compared with gathering, and on average, it makes up 35% of the subsistence base for present-day worldwide hunter–gatherers, independent of latitude or
environment(27,37). For example, hunting by some surviving hunter–gatherers is still not very successful: the probability for a kill in !Kung bushmen is only 23%(37), and the subsistence of Hadzabe, as described by Woodburn(39), consists of 80% plant foods. In the Paleolithic, however, hunting might have been more productive, due to both higher animal biomass and hunter–gatherers not being displaced to marginal environments, unattractive for crop cultivation or cattle. Consequently, we chose the employed ratios within the range of the most commonly observed hunter–gatherer subsistence ratios(26,27).
In other words, if extant hunter-gatherers equipped with advanced stone tools and modern weapons have such low hunting success rates, it's probably not reasonable to assume that Paleolithic ones did much better. They likely relied more on subsistence plant foods and scavenged meats than they did on big game hunting. This notion contradicts a great deal of what I, at least, have seen in my brief sojourns through the paleo-diet realm, where you'd think hominids are descended from wolves or something, the way resident armchair anthropologists lionize paleo-hunting at the expense of paleo-gathering.

For this reason, the team exclude from their studied ranges the possibility of Paleolithic diets gaining more than 70 percent of the their energy from animal-derived sources; a higher percentage seems inconceivable to them, given the technological constraints they note (to their credit). Personally, I'd say even the 70 percent range is being awfully generous, and would set the upper possible range no higher than 50 percent, and even that would be pushing it.

But that's just splitting hairs. What's more interesting to me about this paper isn't which foods it includes, but which ones it leaves out. The team focus their models on the conundrum of whether early man met his protein and fatty acid needs through various ratios of fish-to-plants-to-terrestrial mammal organs; and in doing so, they unknowingly reveal a confirmation bias in favor of the sorts of animals that modern Western humans prefer to eat.

In short, there are no bugs or worms in this paper. It's as though someone took a big can of Raid to the authors' paleo-imaginations. So steeped are they in their Western food bias and paleofantasies that the possibility of Paleolithic man fulfilling his nutrient requirements with a diet of creepy-crawlies never occurred to them.

But it should have. Insects, grubs, worms and other terrestrial invertebrates have long provided humans and other primates with nutrients, and continue doing so today in most parts of the world. The UN, at least, if not the paleo-diet movement, has taken notice.

What's more, insects have essential fatty acid and protein profiles comparable to poultry and fish. There's no good reason terrestrial invertebrates -- hell, let's just call them "bugs" --  should be excluded either from studies or lifestyles that purport to replicate H. sapiens' "ancestral" diet. But they usually are.

For the most part, bugs remain invisible to such researchers, and to the movement they spawned. By and large, paleo-diet bloggers and writers focus on the traditional American meat sources and indulge themselves in fantasies of a Paleolithic populated by spear-toting personal trainers. Bug-eating just doesn't sell books, I guess.

Entomophagy is conspicuously absent from this "paleo-diet" study, as it is from most of the paleo-diet movement that I have seen. And further, this study itself has been conspicuously absent from the "paleo" blogosphere. Both absences tell us more about the confirmation biases and paleofantasies of modern Western humans than the study itself can ever tell us about the trophic strategies of Paleolithic hominids.

I, of course, do not advocate eating insects or any other animals. But that's just me, and a bunch of other wacky vegans. Nonetheless, I'd be interested to see how popular these (allegedly) "paleo"-diet authors and bloggers would remain if they started admitting that the Paleolithic diet was probably more Fear Factor than Fat Head.

At least National Geographic, bless them, was kind enough to lend a pre-emptive helping hand with some handy bug recipes. Eat that, Cordain, Eaton, et. al.

10 May 2011

What's In A Nomen?

I'm considering a name change, both to my handle and to the blog itself. I'd keep the same URL, but part of me thinks the current title gives too much of the wrong impression, as though I'm trying to say there's a necessary connection between paleontology and veganism.

The new name, and possibly the new avatar handle as well, would be The Humane Hominid.

I'd love some feedback from my readers about it. What do y'all think?

07 May 2011

Forks Over Knives: A Reflection

I'll concede, I went in a little dubious. The health argument for veganism ultimately fails, not because veganism is unhealthy, but because framing veganism primarily as a "diet" or medical treatment restricts its appeal to those who are either sick and seeking "alternative" therapies; or vain, and chasing the latest fad. This approach obscures the ethical argument that's the basis of veganism (that applies to everyone), and only nominally makes a positive impact for exploited animals. As Ginny Messina puts it:
The counter-argument to all of this, of course, is that getting people to go vegan for any reason is a good thing. It reduces animal use and it helps shift paradigms about food choices—which can eventually open minds to the issue of animal liberation. I’m in favor of most efforts and campaigns that do those things. But here is the problem with using the health argument in this way—it’s that there isn’t any health argument for veganism.
There is, of course, a pretty good argument for eating more plants (lots more plants) and less animal food, but no one has shown that you must eat a 100 percent plant diet in order to be healthy. So to make an argument for a 100% vegan diet based on health benefits alone, we have no choice but to stretch the truth. We have to overstate the benefits of vegan diets, and sometimes minimize or dismiss the risks. And as soon as we stray from actual facts, our advocacy is on shaky ground.
So, I was glad to see a (brief) interview with Gary Baur of Farm Sanctuary, and a nod (however grudging) to the animal rights argument. I was also glad to see that the film restricts itself mostly to the phrase "whole-foods, plant-based diet" rather than "vegan" (in fact, the only person in the whole film who utters the word "vegan" is Mac Danzig, and you know better than to correct him...). The first because I think the ethical argument should always be front and center, and we shouldn't be playing a shell game with people, tricking them into the subculture. And the second because, as Messina says, the argument for a whole foods, plant-based diet, however strong, is not in itself an argument for veganism.

Mixed feelings aside, I still recommend the film. It's an engaging and moving portrait of Drs. T. Colin Cambpell and Caldwell Esselstyn, and the people whose lives they've saved with their approach. I found it particularly poignant that both men grew up on dairy farms, then had their minds changed by evidence and experience. It helped me see them not as advocates for a cause, but as honest scientists promoting their work.

And thankfully, there's zero talk about homeopathy, naturopathy and other forms of unproven, unethical quackery; and only a brief bit of borderline conspiracy thinking.

Overall, it's a great documentary that will probably convince a lot of people that they need to eat lots more plants. I'm not sure how much it will help the animal rights movement, but at least Mac Danzig will keep kicking ass for the film's audience on TV.

Not a perfect film for the vegan cause, but we can't all be Earthlings.

Back Atcha, PermaVegan! -- Fallback Food Fight, Round 2

Image courtesy of Kenyathropus.com
I should thank the PermaVegan for engaging me in this debate, for it has goaded me into performing one of the most essential elements of scientific thinking: arguing against one's own bias. In contemplating and researching a response to his latest entry, I realized that I, like many vegans, was clinging to the hope that our hominin ancestors were herbivorous. Consciously, I knew this wasn't exactly true, but emotionally, I wanted it to be true. And thus, what I'm about to do feels like a betrayal, even though it isn't. Veganism, as I've said, is a modern ethical stance, formulated in response to modern challenges. What our ancestors ate isn't morally or ethically relevant.

Nonetheless, the PermaVegan asks a good question, in four parts, that deserves a robust answer:
My question, though simple -  "How do you resolve the abrupt evolutionary reversal that appears to be implied in a proposed hominin preference for meat?" - is best introduced in four parts: 

  1. As you read the scientific literature, what is the earliest date (in millions of years ago, or Mya) for which you think it is reasonable to argue that our line of descent was frugivorous/folivorous?
  2. By what date, approximately, do you believe our line of descent can be said to have demonstrated a dietary preference for meat over fruits and vegetables?
  3. How do you argue that a new preference for the consumption of meat over fruits and vegetables arose prior to a generalized or plant-foraging adaptation that only secondarily made meat acquisition a marginally better energy deal in times of fruit and vegetable scarcity?    
  4. As a result of what major environmental and/or genetic modification do you believe the consumption of meat became a more optimal foraging strategy (in net energy terms) than the acquisition of previously preferred plant-based foods?       
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 (as opposed to hominids; see the addendum, below) have always been at least somewhat behaviorally carnivorous.

Before getting into the meat of the matter, as it were, I should offer a few caveats, all of which you should keep in mind whenever you read any article on the subject of diet and human evolution:
  1. The fossil record of hominin evolution is spotty, relying heavily on incomplete skeletal remains and teeth. Thus, conclusions about diet drawn from it are tentative. 
  2. The fossil record is biased in favor of meat-eating evidence. Bones and teeth fossilize more readily than plant material or soft body parts. This, again, is a reason to draw only tentative conclusions about the relative importance of meat in hominin diets; aside from isotopic data (which has its own issues), evidence about the prominence of plant foods in hominin diets simply doesn't preserve as well. Thus, we run the risk of over-stating the case for meat.
  3. The evolutionary relationships between hominin taxa are murky, and still controversial. Anthropologists still argue over which lineages are ancestral to Homo. So, again, conclusions must be tentative.
Bearing that in mind, however, the fossil record does give us good indications of early hominin diets... but the catch is deciding precisely which hominin taxa are directly relevant to the case. It's always been assumed (reasonably) that at least some of the australopithecines were direct ancestors of genus Homo. As a result, the debate over just how carnivorous our ancestors were has tended to focus on the question of which australopith was most likely to be our ancestor. Those who preferred the interpretation that A. afarensis was a direct ancestor of all subsequent hominins gave points to the vegan camp (whether they knew it or not), while those who preferred the interpretation that A. africanus wasn't descended directly from A. afarensis but was ancestral to Homo gave points to the carnist camp (whether they knew it or not).

But, a few recent fossil finds have cast doubt on whether the australopiths were actually our ancestors at all; turns out, they might have just been a sister taxa to the Homo line, and thus an evolutionary dead-end with no direct relevance to us.Which, if true, means that the hominins actually related to us were (slightly) more carnivorous than their australopith cousins.

Consider Kenyanthropus platyops, discovered in 1999 by Justus Erus, working on Maeve Leakey's team (yes, of those Leakeys!) at Lake Turkana, Kenya. This enigmatic hominin discovery sparked a debate that rages to this day. Leakey's team suggested then, and still do today, that Kenyathropus deserved its own genus, and may have been an ancestor of Homo rudolfensis. This suggestion would take Homo out of the australopith line of descent altogether, and turn australopiths into an evolutionary dead-end; a radical move! Understandably, other paleoanthropologists dispute their findings, and the issue has not been settled.

Kenyanthropus and its descendants had teeth adapted to a diet of soft, rich foods like tubers, fruits and meat. And if it really is its own genus separate from australopithecines, as the Leakey team suggests, then its dental adaptations would have been inherited from as-yet-undiscovered, non-australopithecine hominin ancestors going all the way back to the chimp-human divergence. And that means, in turn, that the omnivorous capability of our Homo lineage has been with us for 7 million years.

While we're on the topic of omnivory, now would be a good time to point out another concept that needs clarification: the presumed conflict between a frugivorous and an ominvorous morphology. The PermaVegan -- and many other fellow vegans, as well as most carnist armchair anthropologists -- talk about them as if they are different things, but they're not. At least, not exactly.

Among mammals, herbivory and carnivory are both highly specialized adaptations, viewable in the dental and (among extant species) gut morphologies of the relevant species. Frugivory has always been considered intermediate between the two; as Hladik, et. al., noted in their critique of the expensive-tissue hypothesis:
The “faunivore” trend, as well as the “folivore” trend, are morphological specialization – corresponding to different allometric relationships – that are not likely to allow a large plasticity, as for any specialized character. A specialized carnivorous adaptation in humans that would correspond to a minimized gut size is obviously not supported by our data (fig. 1). Large variations presently observed in human diets (Hladik and Simmen, 1996) are probably allowed by our gut morphology as an unspecialized type of “frugivore”, a flexibility allowing Pygmies, Inuit, and several other populations, present and past, to feed extensively on animal matter, for whom most of the energy is mostly derived from fat (Speth, 1987).
In other words, modern human guts are adapted to a diet of soft, energy-dense foods, a condition they inherited from "frugivorous" ancestors but that accidentally also allows them to be better at digesting meat than other primates.  To put it succinctly, H. sapiens are functionally omnivorous because of their frugivory, not in spite of it (a point that threatens to undo the whole debate before it even starts)!

A final point to consider before I answer the PermaVegan's question directly is one I've raised before: the behavioral distinction between "herbivore," "omnivore" and "carnivore" isn't always clear-cut, and isn't always a reflection of skeletal or gut specializations. Witness, as evidence, the strange case of the meat-eating deer; or the lovable panda, a herbivorous carnivore.

So, in answer to the PermaVegan's core question --  "How do you resolve the abrupt evolutionary reversal that appears to be implied in a proposed hominin preference for meat?" -- I'd contend there really isn't any "abrupt reversal" that needs resolving. 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. The burden of proof, I'd say, rests with those who contend that meat-eating is somehow anomalous among hominins... especially if the K. platyops evidence turns out in favor of the Leaky team's interpretation.

Of course, an ancestral behavior of meat-eating does not necessarily imply that meat made up the bulk of an extinct hominin species' daily diet; a great deal remains open to interpretation, and bias can always creep in. Which brings us to the PermaVegan's sub-questions:

1) As you read the scientific literature, what is the earliest date (in millions of years ago, or Mya) for which you think it is reasonable to argue that our line of descent was frugivorous/folivorous?
I'd say our line of descent has been frugivorous (not folivorous! -- they are different adaptions, and using them in the slash style, implying they're the same thing, is inaccurate) since about 55 Ma, during the Eocene radiation of the adapiformes. Many of these animals' descendants developed folivorous capabilities, it's true, but that's when the first reasonably-identifiable frugivorous adaptations (as distinct from their insectivorous ancestry) are notable.

2)By what date, approximately, do you believe our line of descent can be said to have demonstrated a dietary preference for meat over fruits and vegetables? 
Subject to the caveats I offered earlier, I'd say around the same time as the PermaVegan and professional researchers do -- ca. 2.5 to 1.5 Ma. That's when the fossil record gives us robust, somewhat direct evidence that hominins were eating other animals. But again, it's likely this behavior has been with us right from the start.

3) How do you argue that a new preference for the consumption of meat over fruits and vegetables arose prior to a generalized or plant-foraging adaptation that only secondarily made meat acquisition a marginally better energy deal in times of fruit and vegetable scarcity? 
Again, I'd argue that hominins have always had some preference for meat, and there's nothing "new" about it. This can be inferred from observations of chimpanzee hunting in the wild, and the fossil record of our dental development.  My working mental model is that early hominins relied on fruit and tuber foraging most of the time, but snatched the opportunity for meat whenever they could... in a strategy similar to that of modern chimps.

4) As a result of what major environmental and/or genetic modification do you believe the consumption of meat became a more optimal foraging strategy (in net energy terms) than the acquisition of previously preferred plant-based foods? 
The earliest robust evidence for hominin meat-eating appears towards the end of the Pliocene global cooling, which saw the decline of rain forests and the spread of arid grasslands and savannahs; and extends into the cold Pleistocene. The first hominin dental adaptations to a rich, soft-food diet appear a bit earlier than that, in the mid-Pliocene with K. platyops. I'd say that's when the shift began to happen, and wouldn't want to get more specific than that, because I don't think such a shift would have been "abrupt," as the PermaVegan described it. As noted, it's my evaluation that hominins have always had some preference for meat.

I realize this may not be what a lot of vegans want to hear. It's not what I want to hear, either. In my heart, I wish we had descended from purely herbivorous ancestors; if nothing else, it would make the case for veganism a bit easier. But I cannot ignore the evidence of the fossil record; that would be intellectually dishonest. The case for veganism -- or at least, my case for veganism -- isn't built on the details of human evolution. It doesn't have to be. The systems of animal and environmental exploitation we face today are unprecedented, and veganism is a form of conscientious objection from those systems. That it didn't exist in coherent form prior to the modern age should not trouble vegans any more than the absence of ancient Roman skyscrapers troubles architects.

ADDENDUM: Some readers may be confused by use of the words "hominid" and "hominin." The difference is easy to remember, though. Hominin refers to the ancestral line of Homo and all of its sister taxa except the great apes. Hominid includes Homo, its hominin relatives, and the great apes (and their ancestors). So, chimps and humans are both hominids, but only humans are hominins.

06 May 2011

Your Inner Fish Is All Over Your Face

Well, okay, it's mostly just on your philtrum, that little groove that runs from your nose to your upper lip. If you're like most people, you see it in the mirror every day and don't think much of it. If you're like me, you sometimes wonder, "WTF?"

Well, turns out the philtrum is an evolutionary remnant of our descent from bony, lobe-finned fishes. The BBC has an awesome (though unfortunately un-embeddable) video up today about the formation of the human face during gestation, when we go from looking like one of our fish ancestors to looking like us.

It's a bit freakish to look at, but all the more mesmerizing for it. The accompanying article also explains the fishy origin of hernias and hiccups, but they're explored much more in depth by Neil Shubin's excellent book, Your Inner Fish.