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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 August 2010

(Cave) Man vs. (Cave) Bear

A new study provides more evidence for the Overkill Hypothesis:
The cave bear started to become extinct in Europe 24,000 years ago, but until now the cause was unknown. An international team of scientists has analysed mitochondrial DNA sequences from 17 new fossil samples, and compared these with the modern brown bear. The results show that the decline of the cave bear started 50,000 years ago, and was caused more by human expansion than by climate change.
On the other hand, another new study -- this one from the field of paleobotany -- provides evidence for the Climate Change Hypothesis of Pleistocene Extinction.

I still back the Overkill Hypothesis, because I think the bulk of the evidence supports it. But, I am not immune to confirmation bias, so I provide you, dear reader, with evidence from both camps.

24 August 2010

Why I Won't Debate Most Commenters

Another Anonymous turned up here today, and demanded evidence for something. It's pretty clear that they haven't read most of the posts here, or even most of the post to which they responded, but that's beside the point.

I'm just taking this as an opportunity to announce my Comments policy. I won't debate most commenters, regardless of their points. This isn't because I fear "losing," but because there's nothing to be gained by the effort.

Today's daily dose of Vegan Outreach sums it up well:
But our goal isn't to show how awesome veganism is; what is important is saving animals. To do this requires an honest evaluation of reality, from the nutritional aspects of veganism to the possibilities and psychology of how people can and do change.
Of course, if a commenter points out genuine errors, grammatical issues, or unclear writing, I will of course respond with thanks and corrections.

But I'm not here to argue. I'm here to share my love of paleontology and my love of animals, in the hope that doing so will inspire others onto both paths.

23 August 2010

Sex and the (newly-)single paleobotanist

BBC profile of early feminist Marie Stopes. Thankfully, it focuses equally on her contributions to paleobotany and women's sex ed.

22 August 2010

R.I.P., E.T.H. (Expensive-Tissue Hypothesis)?

My brain won't let go of my post about the new Ethiopian hominid find. As a result, I've gotten no work done on the dinocephalians installment of History Of Your Teeth. I'll get to that next week.

Here's what's nagging me:

You'll recall John Hawks opined that the discovery undermined the popular Expensive-Tissue Hypothesis, or ETH. The ETH is often wielded by carnists as proof that humans must eat meat, in order to fuel our large brains; and further, that it proves meat-eating kick-started and drove hominid brain development through the Pleistocene. In short, the ETH is summarized in popular language as "meat made us smart" (though that was never actually what its authors argued).

It occurred to me that some readers of this blog may not quite get what Hawks meant by commenting that,
(a) 2.6-million-year-old butchery tradition should already have refuted the hypothesis that meat-eating caused the expansion of brain size in Homo. ... the observations Braun points out pretty much demolish the 15-year-old story of 'expensive tissue.' Australopithecus seems to have had a small gut, and a bigger brain than chimpanzees. If there was a tradeoff, A. afarensis had already made it.
So, here's some background on the ETH, followed by my thoughts on its destiny.

The ETH was first proposed by Leslie C. Aiello and Peter Wheeler in 1995, who argued that the human brain had such a high metabolic cost that it could only be maintained through a trade-off of energy from other metabolically expensive tissues, thus making those other tissues smaller than they'd otherwise be. As they put it in the abstract to their initial article, The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution [1]:
Brain tissue is metabolically expensive, but there is no significant correlation between relative basal metabolic rate and relative brain size in humans and other encephalized mammals. The expensive tissue hypothesis suggests that metabolic requirements of relatively large brains are offset by a corresponding reduction of the gut. The splanchnic organs (liver and gastrointestinal tract) are as metabolically expensive as brains, and the gut is the only one of the metabolically expensive organs in the human body that is markedly small in relation to body size. Gut size is highly correlated with diet, and relatively small guts are compatible only with high-quality, easy-to-digest food. The oft-cited relationship between diet and relative brain size is more properly viewed as a relationship between relative brain size and relative gut size, the latter being determined by dietary quality. No matter what is selecting for relatively large brains in humans and other primates, they cannot be achieved without a shift to a high-quality diet unless there is a rise in the metabolic rate. Therefore the incorporation of increasingly greater amounts of animal products into the diet was essential in the evolution of the large human brain.
Many people have read this to mean that "meat made us smarter," but that is not quite what Aiello and Wheeler meant. As Aiello put it in another paper (emphasis added),
Food of low digestibility requires relatively large guts with elaborated fermenting chambers (stomach and/or small intestine) while food of high digestibility (such as sugary fruits, protein and oil rich seeds and animal material) requires relatively smaller guts characterised by simple stomachs and proportionately long small intestines. ...This strongly suggests that the observed association between diet quality and relative brain size (Parker and Gibson, 1979; Clutton-Brock and Harvey, 1980; Milton, 1987, 1988, 1993; Leonard and Robertson, 1992, 1994, 1996) is really a relationship between relative brain size and relative gut size, the latter being determined by dietary quality. The main conclusion is that no matter what is actually selecting for increase in brain size in humans and non-human primates, a high quality diet is necessary for encephalization. It relaxes the metabolic constraints on encephalization by permitting a relatively smaller gut, thereby reducing the considerable metabolic cost of this tissue.
So, a "high-quality diet" need not necessarily be one composed mostly or even exclusively of animal foods. Aiello clearly argues that an increase in meat-eating drove encephalization, but the definition she offers is not dependent upon meat-eating. If Richard Wrangham's cooking hypothesis turns out to be right, it could very well be the case that the high-quality diet needed for the ETH was based, at least at first, on cooked fall-back foods like roots, tubers and seeds, along with fresh fruit, supplemented by scavenged meat.

It is possible to read too much into this qualification, however, and allow wishful vegan thinking to shape our analysis. The temptation to paint our ancestors as peaceful frugivores is strong in the vegan community, and we may end up rejecting the ETH for purely emotional or fanciful reasons. This, as I've said before, is a trap. So, we need to be honest with ourselves. Whatever the veracity of the ETH, there is no doubt that hominids ate other animals, at least some of the time. Any vegan who argues otherwise is misinformed, and will get soundly trounced in a discussion with informed carnists.

But that doesn't mean we need to acquiesce to the ETH, either. There are legitimate, non-vegan-related reasons to question it, and that's what Hawks was driving at.

Indeed, one of the ETH's fundamental assumptions might be mistaken.

The ETH depended, in large part, on the observation that hominid brain evolution was punctuated by two sudden growth spurts, one at about 2 million years ago (coinciding with the first appearance of the genus Homo), and another at about 500,000 years ago (the appearance of the species Homo sapiens). Each event, it was held, was powered by adoption of increasingly high-quality diets, usually presumed to be meat-centered.

That was the theoretical landscape 15 years ago. Since then, several new fossil finds, and new interpretations of older fossils, have changed the landscape, and it is no longer clear that hominid brain evolution was punctuated. And the dividing line between Australopithecus and Homo is getting blurrier by the day.

Dean Falk of Florida State University sums it up well (emphasis added):
Although brain size remained conservative during the evolution of Paranthropus, it increased in Australopithecus and between the latter and specimens that lived more recently (~ 1.7-1.9 ma) in Africa and the Republic of Georgia. The overall morphology of these more recent specimens is transitional enough so that some workers place them in Australopithecus while others include them in early Homo (Balter & Gibbons 2002, Wood and Collard 1999). If, indeed, these specimens are transitional, then the received wisdom that brain size suddenly ‘took off’ in the genus Homo around 2.0 mya needs serious reevaluation (Falk 2004b, Falk et al. 2000).  Thus, rather than there being a jump in cranial capacity in early Homo, cranial capacity may have begun increasing in the Australopithecus ancestors of Homo a million years earlier (Falk et al. 2000).  With the redating of Java sites (Swisher et al. 1994, Huffman 2001) pushing certain cranial capacities further into the past, there is no longer the discontinuity in the trend for increasing cranial capacity (Falk 1987b, 1998) that once contributed to the suggestion that brain size evolution underwent ‘punctuated’ events (Hofman 1983, Ruff et al. 1997, Leigh S, 1992). Rather, the recent discovery of LB1, the small-brained type specimen for Homo floresiensis (Brown et al. 2004, Morwood et al. 2004), lends an entirely new perspective to the study of hominin brain size evolution (Falk at al. 2005): From australopithecines through extant Homo, upward selection widened the range of brain-size variation, while australopithecine-sized brains may have continued to provide the lower boundary (at least, until very recently). Thus, to some extent, Fig. (12.)3 encapsulates the interplay between selection for brain size (vertical vector) and selection for neurological reorganization (horizontal vector).
The Figure (12.)3 Falk refers to provides two charts.  The one on top plots cranial capacities for select hominins against time, and includes among them the genus Paranthropus (robust australopithecines), who are generally not considered ancestral to Homo. On this chart, the pattern for brain size displays the punctuated pattern mentioned earlier, appearing flat until around 2.0 Ma, then increases suddenly with the emergence of Homo.

The bottom chart, however, only plots brain sizes of hominids thought to be ancestral to Homo; that is, it leaves out Paranthropus. And here the pattern looks very different -- a steady, non-punctuated, linear climb beginning ~1.0 million years before the emergence of Homo. No sudden leaps upward.

In short, the top chart's data -- showing punctuated evolution of brain size -- is skewed by the inclusion of hominin genera and species not considered to be our ancestors. When we include only our own ancestral line, there appears to be no sudden leap in brain size, after all.

The recent discovery and description of Australopithecus sediba has only muddied the waters even further. At least one researcher is arguing that the genus Australopithecus should be sunk altogether. He reiterates his case in response to the stone-tool-using find from Ethiopia.

In this context, it looks like the ETH may turn out to be what John Langdon called an umbrella hypothesis: an attempt to explain a multitude of human features by means of a single adaptive breakthrough, with an hypothesis that appears parsimonious, but isn't. The ETH's fundamental assumption that human brain evolution was punctuated looks less likely today than it did 15 years ago.

In short, if the evolutionary pattern of hominid brain size is steady rather than punctuated, and if butchery and meat-eating have been part of hominid behavior since the days of the australopithecines, then the likelihood that meat-eating and hunting sparked sudden increases in cranial capacity goes down considerably.

This is not to dismiss the ETH out-of-hand. It's a serious and legitimate hypothesis, with experimental support in the literature (unlike the Aquatic Ape Theory for which Langdon coined the phrase). It may turn out to be true; many other respected theories began this way. But the appeal of its simplicity is also its danger.

Right now, the ETH does not offer a mechanism for how, precisely, increased meat-eating made hominids smarter. To be fair, Wrangham's elegant and appealing cooking hypothesis doesn't, either. Nor does the new, trendy theory linking brain evolution to climatic cooling. All they do is point to compelling evidence that their pet factor removed an energy constraint on brain evolution. But energy budgets cannot explain everything. Without a mechanism, an hypothesis remains limited in its veracity.

The future fate of the ETH is worth watching. I suspect it will pass on once all the taxonomic confusion about hominids is cleared up, and a clearer picture of our evolution takes shape.

But then, I could be wrong.

Notes
[1] Aiello, L. C., & Wheeler, P. (1995). The expensive-tissue hypothesis: The brain and the digestive system in human and primate evolution. Current Anthropology , 36 (2), 199.
URL http://dx.doi.org/10.1086/204350

21 August 2010

14 August 2010

A. afarensis may have eaten meat; so what?

I suppose it's inevitable. I suppose I bring it on myself. Whenever people learn that I am both an ethical vegan and a paleontology student, they throw meat-eating cavemen in my face. I have hence adopted the habit of pre-empting these inquiries by keeping abreast of developments in the study of hominin diets, even though hominin evolution isn't really my primary interest.

The latest discovery out of Ethiopia is sure to add another arrow to carnists' quiver. An article in the New York Times sums up their announcement:
Scientists who made the discovery could not have been more surprised. They said the cut marks on a fossilized rib and thighbone were unambiguous evidence that human ancestors were using stone tools and sometimes consuming meat at least 800,000 years earlier than previously established. The oldest confirmed stone tools are less than 2.6 million years old, perhaps only a little before the emergence of the genus Homo.
The evidence offered for their conclusion is a series of cutmarks and one percussion mark on two bovid bones. The authors run through a battery of microscopic tests to rule out other sources of the cutmarks, such as trampling by other animals, and conclude that the marks could only have come from australopiths using sharpened stones to scrape flesh off of the bones. If true, the discovery would substantially revise our understanding of australopith diet and behavior. The current consensus is that A. afarensis was largely herbivorous, thriving on fruits, seeds and tubers, with supplementation by insects and such, and perhaps a bit of meat-scavenging when opportunities arose. But this discovery could show that australopiths developed tool-use and pre-meditated meat-eating before Homo did.

Thankfully, the NY Times piece offers up the proper skeptical response from other scientists:
Still, the discoverers are already being pressed to defend their interpretation that the cut marks on the bones are evidence of stone-tool butchery. Tim D. White of the University of California, Berkeley, one of the foremost investigators of early human origins, said flatly that their “claims greatly outstrip the evidence,” and noted, “We have been working sites in this area for 40 years, and not a single stone tool has been found in deposits of this antiquity.”
Sileshi Semaw, a paleoanthropologist at Indiana University who was a discoverer of the oldest confirmed stone tools, from 2.6 million years ago, noted in an e-mail message from Ethiopia that researchers had often been misled by bone markings left by trampling animals and other natural causes. “I am not convinced of the new discovery,” he said.
So, the jury is still out.

This touches on the issue of how vegans should handle the caveman argument. Many of us are tempted to strain credulity and torture the evidence to "prove" humans are "naturally" vegan. This is a trap, and one into which carnists (especially paleo-dieters) would love us to fall; the evidence isn't on our side. There's no doubt that hominids ate meat.

But, it should be remembered that this fact doesn't tell us very much about an "ideal" human diet, either. Paleolithic hominids were opportunistic feeders by ecological necessity, and a capability to do something does not imply either an obligation or a necessity to do it, circumstances being equal.

The argument for veganism has always been primarily ethical, and ought to remain that way. It's based on a concern for the future, not an obsession about the past.

So what if australopiths and early Homo ate animals? While interesting, it says little about what's right or wrong for Homo sapiens in the 21st century, confronted as we are by increasing resource scarcity, overpopulation, and biodiversity crises.

The problem I have with paleo-dieters isn't that they point out prehistoric meat-eating, but that they all seem to think a return to this style of living is both possible and ideal.

I'm skeptical of both claims; given what we know about the Pleistocene mammal extinctions and the  impact of modern hunting, a return to the Paleolithic hunter-gatherer lifestyle is not sustainable. And from a nutritional standpoint, neither it nor veganism are "ideal"; the only "ideal" human diet is likely to be one of our own invention, in the future, borne of increased knowledge and practical application of biochemistry.

So this latest potential ammo for the carnists is much ado about nothing before it even ends up in their arsenal.

UPDATE: Paleoanthropologist John Hawks, writing about the same discovery, offers some interesting thoughts about its implications for the the expensive-tissue hypothesis:
A 2.6-million-year-old butchery tradition should already have refuted the hypothesis that meat-eating caused the expansion of brain size in Homo. But it was still possible to maintain that the initial Oldowan was insufficiently dedicated, or that the anatomical specializations (e.g., small guts) allowing brain expansion took time to develop, or that as-yet-undiscovered large-brained hominins would be found. Any of these are still possible, but the observations Braun points out pretty much demolish the 15-year-old story of "expensive tissue." Australopithecus seems to have had a small gut, and a bigger brain than chimpanzees. If there was a tradeoff, A. afarensis had already made it.

08 August 2010

Oops!

Has paleontology been telling you that chewing motion and heterodontism are distinct synapsid traits?

Oh well. Can't win them all:
An ancient crocodile species has been discovered with molar teeth that fit together much like those of small carnivorous mammals. With lanky limbs, a lack of stiff armor on its back, and a nose ill-equipped for the water, it likely acted much more like a terrestrial cat than a fierce water predator.
...
By contrast, mammals in the northern hemisphere were rapidly diversifying and becoming the ancestors of all mammals alive today. One explanation for the diversity of crocodiles in Gondwana is they were filling niches that were being filled by mammals in the north, O’Conner says.

Vegan Scientist: A Kindred Spirit

Now you may think that the whole fAtkins diet rebranding gets my knickers in a twist because it's contrary to the vegan thing you heard I like. But that's only a small reason, if any. Mainly it's this whole nostalgia for the past that never was. The cartoon version of primitive humans taking a bite out of a mammoth simply isn't true. ... The concept is just a continuation of the whole natural-is-automatically-good-for-you mantra that just bugs the heck out of me (arsenic, uranium, strychnine, poliovirus, all natural! they must be good for you!)

Veg Lab Rat is a protein biochemist and a vegan, who works at a government lab.

Vist his/her blog and send some love. I know I'm about to.

March Of The Pelycosaurs: The History Of Your Teeth, Part IV

From A. florensis' humble origins, things start to get... well, really scary with the protomammals.

I'll be honest. When I was a kid, something about Dimetrodon frightened me, much more than any dinosaur. I used to think of them as "land sharks," and after a few too many viewings of "Jaws," I had a hard time shaking my fear of any large animal with big teeth and a fin on its back.  I mean, check this sucker out:
Courtesy of http://www.nhm.ac.uk/

How would you like to see that creature charging you from the underbrush? Raptors? Meh.

Of course, that was before I really understood my kinship with these scary beasts, before I learned that they were very likely my direct ancestors. And now, though I disapprove of their dietary choices (wink), I have moved from a place of fear to a place of respect. After all, it's a safe bet that I, and you, and your dog, too, have one of these critters somewhere in our family tree.

Dimetrodon is just one of several genera who split off from A. florensis' line in the early Permian to become the dominant terrestrial life-forms on the new supercontinent of Pangaea. But sadly for them, that time was geologically brief.

The relatives of A. florensis -- the ophiacodontids -- diversified and radiated across the tropical belts towards the end of Pennsylavanian (Carboniferous) times, giving rise to two new clades of often sail-backed animals, the edaphosaurs and the sphenacodonts. And here again, we see a variety of tooth shapes in one mouth.

The edaphosaurids were probably the first tetrapods -- and certainly the first amniotes -- to evolve herbivory. We vegans might like to think our ancestors sprung from these humble leaf-munchers, but unfortunately, our heritage goes through the line of the sphenacodontids, predatory monsters with big, sharp teeth. But not to worry; evolution is a varied and splendored thing. Our story will witness the rise of many more herbivore and frugivore ancestors over the 300 million years or so that follow these animals... and some of them are closely related to us.

Anyway, the edaphosaurs and the sphenocodonts, despite the differences in their dietary strategies, were closely related. A comparison of their skull structure reveals they were clearly sister groups sprung from a common ancestor:
Courtesy of Palaeos.com
One thing to note about the chart at left, that isn't pointed to directly, are the teeth of each specimen. The edaphosaur teeth are relatively uniform, as befits their basal herbivorous adaptation.

But Dimetrodon's teeth are all over the place. Her very genus name, Dimetrodon, actually means "two-measured teeth," and was given to her because her side and rear teeth are much smaller than those of her forejaw. And like A. florensis (and many protomammalian and mammalian descendants to follow), she had pronounced canines.

But heterodontism was not unique to the Dimetrodon genus. All of her sphenacodont relatives displayed the same feature. And it's a pattern that will repeat itself, time and again, as we trace the history of our teeth through the Age of Dinosaurs to the present day. Paleontologists call this repeated handing-down of ancestral traits a plesiomorphy, which is just a fancy way of saying that you've got a lot of junk in your evolutionary trunk that you may have found new uses for, but wasn't necessarily put there so you could use it the way you do. It's a subtle undermining of the argument from design so common in debates about evolution. Critics want to make a big deal out of some particular trait of humans (say, our canine teeth), as evidence that nature "intended" us to do some particular thing. Paleontology responds with, "eh, so what? Only reason you've got that is that your ancestors did. It's no big deal."

The edaphosaurs and sphencaodontids escort us into Permian time, witness to the formation of the grand supercontinent Pangaea... which would, sadly, be their undoing. The pelycosaur dynasty begins to disappear from the fossil record in early- to mid-Permian time, but not before passing on its legacy to the next great dynasty of protomammals -- the dinocephalians. We'll meet them next time.

01 August 2010

Myths About The Vegetarian Myth

There's a new blog on the block, dedicated to debunking Lierre Kieth. It's worth watching.

Dimetrodon, whose name means "two-measured teeth."
In other news, I am hard at work on my next post in the History of Your Teeth series. Here's a nice image of someone you're going to meet then. She's relatively famous, and often mistaken in pop culture for a dinosaur; however, like your cousin A. Florensis, she was not a reptile, and pre-dated the dinosaurs by about 100 million years.

She was also, quite likely, your direct ancestor. If you're the praying or meditating type, honor her in your next quiet-time.