Monday, August 16, 2010

Ten scratches on two bone fragments distinguish vegetarians from carnivores


It seems like everyone wants to know when we started eating animals, and why we started eating animals, and how that affected our evolution downstream. (Or, if you’d rather, upstream.)
Even if they’re not intrinsically interested in human evolution, most people (including Ozzy over there) still want to learn more about some of our species’ favorite pastimes: Eating and killing things.

If you're ever visiting the gorillas at the zoo, it's pretty obvious what humans are interested in. Of the juvenile chewing on lettuce and carrots, a mother says to her toddler, “Look sweetie, he’s eating his vegetables like a good little boy,” and a teen-aged girl says to her brother, “See, they don’t eat meat and since we share, like, most the genome with them we shouldn’t eat meat either.” Of the silverback male sitting quietly in the corner, a man observes, “Dude’s large and in-charge. I wouldn’t want to [bleep] with that. He’d kill the [bleep] outta me.”

Most of the profound pronouncements you’ll hear at the zoo’s mirror for humanity are centered around food and violence.

Likewise, many, if not most, of the big-picture explanations for human evolution—for why humans are the way we are, for why humans are unlike other apes—revolve around eating and killing animals. Just to name a few…We walk upright to carry and throw things like tools, which are presumably used for hunting prey and processing carcasses (Darwin).We walk upright to move about as terrestrial foragers (which at some point begins to include scavenging and hunting) on the open savannas (The Savanna Hypothesis). Humanity was born in a hunting past (Washburn and Lancaster). Big brains were able to evolve because of the supplemental nutrition and calories obtained through scavenging and hunting (just about everyone). Scavenging, hunting, and stone-tool manufacture require a larger, more cognitively complex brain (just about everyone).

So it makes sense that paleoanthropologists are desperately searching for evidence of our ancestors eating animals. Especially very early evidence. And, in order to find it, you’ve got to not only collect every scrap of bone that you see while you survey or that you dig up while you excavate, but you’ve got to scrutinize each one of those scraps, preferably under a microscope.

Otherwise, you might miss something like the ten scratches on two bone fragments (one rib and one femur) that were just recently reported in Nature.


These artifacts from the site of Dikika in the Afar Region of Ethiopia are the earliest evidence of hominin (human ancestor) meat-eating. What's more, they're the earliest evidence by nearly one million years! Normally finds in paleoanthropology beat-out others by a mere fraction of this quantum leap.

Cut-marked bone at 3.4 million years ago takes the title of First Meat-Eater away from the genus Homo (Homo habilis, Homo erectus,.... , Homo sapiens) and gives it to the only hominin species known at the time from that region of Ethiopia: Australopithecus afarensis, known for being Lucy’s species.

If you're not quaking in your seat right now, well, then you have got some serious nerding-up to do. This is kind of HUGE: Lucy’s relatives, and maybe Lucy herself, not only used stone tools but used them on big mammal carcasses!?

Until this discovery, all we had were stone tools at 2.6 mya and cut-marked bones at 2.5 mya and everyone was content in thinking that the major behavioral shift associated with the human genus, Homo, was obtaining ever-increasing amounts of animal fats and proteins into our diets. That's the best way to make sense of the trend for encephalization which is so much more pronounced in Homo than in previous hominins (where brain sizes were basically chimp-like for the four million years that our ancestors were undergoing selection for increasingly efficient bipedal locomotion).

And see... that has been a little bit of problem: Why would natural selection continue to hone our bodies for bipedal locomotion if not to use them for hunting? With this new evidence for meat-eating earlier in our past, bipedalism makes a lot more sense. At least from the traditional standpoint.

But you’re probably thinking… ten scratches on just two bones? Well, it’s come down to less than this before. When the evidence is good, you certainly don’t need more than a meal’s-worth to show that an animal was butchered with stone tools.

Even if those stone tools were not shaped or chipped or flaked first, even if they were just rocks that somebody grabbed from a dried-up riverbed, nobody but us and our ancestors uses/used stone tools on animals. (Okay, otters use rocks to bash open sea urchins and other snacks but not bones of East African bovids.) Chimpanzees use rocks to crack open nuts, but when they occasionally hunt prey they either use sticks as spears or they simply use their strong bare hands, like baboons are known to do as well. So, bones with scratch marks that were made by stone tools can’t be interpreted any other way than to have been made by human ancestors, or at least relatives of our ancestors (collectively termed hominins or hominids, depending on preference).

Except, EXCEPT!, there are some who would still disagree and they may make the following arguments:

1. Carnivores, like lions and hyenas, can scratch bones of prey with their teeth and if those bones aren’t crushed to smithereens as part of the meal, then they can be discovered millions of years later and trick paleontologists. Okay, but that old chestnut’s been cracked wide open. Microscopic details that distinguish tooth scratches from tool scratches have been established and these bones weren’t scratched by teeth.

2. At any time after the animal’s death, its bones could have been trampled and that could explain the scratch marks. Okay, but again, under a microscope and x-rays, those marks differ from the marks left by tools and, again, these bones weren’t scratched by feet.

So what does this mean for our reconstruction of human evolution?

Well, first of all, like we discussed after the Malapa hominins were announced, the genus Homo is probably going to have a makeover here soon. As of now, the earliest members of the genus Homo are no older than 2.4 million years ago. And now that there are three sites (Bouri, Ethiopia at 2.5 mya, Gona, Ethiopia at 2.6 mya, and now Dikika, Ethiopia at 3.4 mya) with stone tools or cut-marked bones that precede the appearance of Homo fossils, either the behavioral or the anatomical criteria must change or both.

We must now accept the idea that eating meat had a much earlier involvement in our evolutionary history than we thought.

It also means that australopiths, with their ape-sized brains, were performing activities that we have always considered pretty difficult. And this cognitive complexity came not only without the aide of human brains but without the aide of human trainers!

And finally, if you ever have a chance to have Lucy over for dinner, now you know what she likes: BBQ ribs and rump roast. Good thing, because vegetarian dinner-party guests can be so persnickety and, oh boy, does that beat the heck out of underground storage organs!


References
Shannon P. McPherron et al. 2010. Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature 466: 857-860

50 comments:

Ken Weiss said...

Another great and meaty post, Holly! Our obsession with violence and carnivory is at least in part a cultural trait. Matt Cartmill wrote a fine book about this, A View to a Death in the Morning, arguing that this obsession reflects a male, culture-based bias.

In the 1970s and before 'Man the Hunter' had been the image of ourselves (at least, that perpetrated by anthropologists). Then it was shown, rather convincingly it seemed, that the great majority of our diet was vegetable rather than meat, and that hunting and killing were not the center of all our affections during the countless millennia of our hunter-gathererhood. In fact, at that time, during the peak of feminism, the pressure was on to change the phrase to gatherer-hunter.

The image of Pleistocene european Big Hunter Heroes was somewhat blunted by various studies at the time, too.

So maybe the new find shows that we did hunt. But it doesn't show that the guys did most of the shopping, and that they never got far from the butcher's counter.

Texbrit said...

Now we just need to find archaeological evidence for the onset (some years after this, obviously) of the "OMG I can't kill it because it's so cute" reflex.

occamseraser said...

Very nice, insightful post. Tx.

C. Marean's participation in this diagnosis also adds credibility (at least for me) wrt cutmarks. Even if this is a rare event that can't be generalized to every australopith, it speaks to the surprising capabilities and broad behavioral repertoire of some under-encephalized early hominins. Hmmm, small-brained, tool-using bipeds -- now, where have I heard that impossible combo before?

Meat consumption need not imply hunting in the strictest sense, as in ambushing or chasing down game. Although chimps do indeed hunt! (forgive me, I used a chimp analogy, which is forever forbidden after the Ardi extravaganza!) Pursuit hunting may still have occurred much later ...

To Homo or not to Homo? meh

Ken Weiss said...

Yes, from a strict Darwinist point of view, how could that reflex have led to higher reproductive success? I'm sure that Just-So storytellers already have answers.

Maybe the women liked guys who were protective like that, because they would not have to fear that if they mated with them, they'd end up eating their babies. So the guy got her pregnant, then went out and slaughtered whatever helpless animal he could find.

As long as he skinned and processed it before bringing it back to the hearth, she could pretend it, too, wasn't cute at the moment of truth.

Holly Dunsworth said...

Thanks everybody for taking the neglected bit on hunting and violence further - Just what I was hoping you'd do!

Ken Weiss said...

Yes, now suppose some anthropologist (undoubtedly someone like Sarah Hrdy) found the same scratchy bones and had proclaimed that this was evidence for women (were Australopithecine females 'women' or what?) testing out knitting needles. Would that have made the Times?

Holly Dunsworth said...

And how fitting that my review on early genus Homo (which is now derailed thanks to these cutmarked bones) came out today!
http://www.springerlink.com/content/e0n8486266478018/

Holly Dunsworth said...

Men knit beautiful things.

Holly Dunsworth said...

http://www.youtube.com/watch?v=2jYa_rJyG18&feature=player_embedded#!

Ken Weiss said...

Well, Anne herself is an incredible knitter, but she's a girl and that's OK. The point is not that he-men can be deft with the needles, but that that would never sell as THE explanation for human evolution!

Holly Dunsworth said...

LOL!

Anne Buchanan said...

Great YouTube link, Holly! And here's one back, one of my favorite blogs: http://queerjoe.blogspot.com/

Ken Weiss said...

This is all VERY disturbing! The fall semester is about to start, and I have to teach 150 students in Human Genetics, where I take an evolutionary perspective.

If I have to sissify this course, half the students (the males) will drop it. I mean, Man the Knitter? Come on! Thumbs evolved not for throwing huge hand-axes, and wielding lethal spears that could kill elephants, or slaughter the guys in the neighboring village because of their religion--but for knitting?

Let's be serious and (even if it's true) suppress this heresy!

Holly Dunsworth said...

LOL!!

Ken Weiss said...

So let's get this straight. The big, hulky, tool-wielding guy hunts, finds, and mangles some poor ungulate that was just out there on the veldt trying to make a buck (pardon the pun).

The Australopithehulk then eats the meat and he hauls the bones back to the campfire. There, his trusty wife is waiting (knitting patiently) for his return. She gives him some mashed mongongo nuts (not even a cold drink).

Eagerly, he whacks the bones open, so she can slurp out the raw, by now rather rotted marrow.

Now let me get this straight: This makes her want to shack up with him? This is not very plausible at all, I must say.

occamseraser said...

A less generous interpretation can be found here:

http://anthropology.net/

Ken Weiss said...

Well, the conclusion is that this crock is a croc? Holly and you ('eraser) are better judges of the facts,but the idea of scientists and journalists rushing to publish and get credit for some dramatic finds is a generic problem these days.

Humans have always been vain in their times' own ways, so what we see today (and blog-post against often) is just part of life. The
system today does not reward modesty.

But there is no reason to cave on that score rather than resist and hope people can be kept to at least a somewhat higher standard.

J. Heath said...

Okay, but going back to the bit about meat eating steadily increasing to build a bigger brain in genus Homo...

Since this latest evidence shows that australopithecines were carnivorous, wouldn't the argument then turn on the idea that genus Homo bankrolled their head expansion by using fire to get more out of the food they were eating? So maybe it wasn't just carnivory that allowed for the big-brain feedback loop, but carnivory plus fire control?

Koobi Fora is still the earliest evidence of controlled use of fire, no? And that's, what...(checking my lecture slides, and I agree with Ken, too close to be start of the semester for this to come out)...1.6 million years ago? Seems like this kind of strengthens Wrangham's case for the importance of cooking for Homo erectus. Don't you think?

Texbrit said...

Any Autstalopithehulk who could not only drag home the killed ungulate but also knew how to do the washing-up afterward, had it made with the Australopitheladies.

Holly Dunsworth said...

McPherron et al cite the croc paper so it's not like they weren't aware of the possibility (nor would they have been, I'd imagine, even if the paper didn't exist).

Holly Dunsworth said...

Heathrow- Cool.

Holly Dunsworth said...

Also, we now have at least TWO vocal and prominent skeptics from Institutes located in their apartments.

Holly Dunsworth said...

http://www.sciencefriday.com/program/archives/201008134

Holly Dunsworth said...

Look, I'm not a taphonomist and I haven't seen the stuff. All I can do is trust their results (as they are experts) but be safely skeptical too, until more results support theirs.

Holly Dunsworth said...

Regarding the Science Friday piece (linked above)... wow. DeGusta's argument invoking probability (notice I did not capitalize that word) is ridiculous. Just because something is unlikely to be found does not mean that when it is found it is dismissible. That is a weak argument that takes away from potentially stronger ones questioning the actual analysis.

Holly Dunsworth said...

Ken wants me to say that the Science Friday thing is an audio file, not something you read.

occamseraser said...

"Also, we now have at least TWO vocal and prominent skeptics from Institutes located in their apartments."

OUCH --LOL!

DeGusta is true to form. Self-awareness isn't his strength. He's playing Tim White by proxy on this one...

Holly Dunsworth said...

check out the interesting comments here:
http://www.nature.com/nature/journal/v466/n7308/abs/nature09248.html#supplementary-information

Jen Hodgson said...

Thanks for the great post Holly!
This find is so exciting, but when I think about it, not all that surprising. Meat eating had to start sometime before we find the big concentrations of cutmarked bones made by early Homo, and considering chimpanzees use tools for very basic things like cracking nuts (and not so basic things like stabbing bushbabies), its not hard for me to imagine an australopithecine coming upon a carcass and using a sharp stone to slice off some meat. It probably happened sporadically long before hominins really got the hang of butchering carcasses.

I’m not so sure this will require the behavioral criteria for the genus Homo to be redefined, since the earliest evidence for *systematic* butchery can still be attributed only to this genus. We do not have any flaked stone tools associated with australopithecines, and that there are only two cutmarked bones out of probably thousands from the same time period seems to indicate meat eating was probably not a major pastime for our ancestors yet.

The pics of the cutmarks themselves look pretty convincing to me (and not BTW like croc tooth marks), but I will be more convinced of their broader implications if we find a few more.

Holly Dunsworth said...

Thanks Jen. Great comment.

Here's what I've been thinking about since posting this...

The claims aren't that extraordinary from everyone's perspective. For people who aren't surprised that some early homs could grab a rock and use it on a carcass before they started doing it systematically, these aren't extraordinary claims.

Finding evidence of rare behavior sure is extraordinary, but then again finding any paleo evidence is extraordinary.

So, if it's shocking to someone that Lucy did this, then it could be argued that the evidence isn't good enough to support such an extraordinary claim.

But, for people who aren't shocked, then ten scratches on two bone fragments is enough to say, okay they did it at least once and that's expected.

Shoulder shrug.

Wait for more study of the material from outsiders and wait for more discovery.

If it turns out, based on additional analyses, that the evidence offered by McPherron et al. doesn't support their claim (or at least that it fails to falsify other possible explanations) then Nature should be really ashamed of themselves.

Really ashamed!

Ken Weiss said...

If chimps hunt and even do it with tools, as I understand the evidence, then it could have even a much deeper history, not specific to hominins. But the point that even if the current interp. is correct, it is not the 'first' cut.

We made the too-hasty, too-much comment about Nature's cover in a brief post subsequent to this one.

Holly Dunsworth said...

So it could have been extinct chimp relatives who made the Dikika artifacts ;).

Holly Dunsworth said...

That's just mean. To say what I said up there. Just mean!

Ken Weiss said...

That, to me, isn't mean. Instead, it is exactly the problem with hyperclaims and hyperjournalism. We need to lower the claims temperature, calm down, and be a lot more humble about what we claim we know.

Holly Dunsworth said...

I'd love to read an outside expert's straightforward evaluation of every possible hypothesis to explain these marks. Hopefully someone will do this soon.

Ken Weiss said...

To many ifs and doubts. Not a good story. Won't stir up 'controversy'. Badly chosen reviewers. Editors are not scientists and don't care, if it gets attention?

Bottom line: as long as things like Nature are magazines rather than journals, they know what is their bottom line.

Holly Dunsworth said...

I deleted the comment just above yours, before you put yours. Sorry if that adds a bit of confusion. :)

Holly Dunsworth said...

So here's a question: Is paleoanthropology a better science because there are so many involved and because of all the scrutiny? Is it better off as a result of all that? Or... is paleoanthropology a worse science because of the claims people are allowed to make in the name of fame and selling things?

occamseraser said...

If you carefully read the detailed supplementary online info, I'm not sure what the beef is here. The scoring methods (with multiple independent "scorers") are clearly explained, other taphonomic agents are considered but rejected (Olduvai crocs included). Marean has a useful comment on the Nature blog in this regard. The Nature cover quip re: "first cuts" presumably wasn't made by the authors, and how anyone could misconstrue that phrase as remotely "creationist" is beyond me. What part of the paper itself -- not comments in the media or words on the cover -- is sensationalist? I don't think you're being fair to the authors. And Nature should be "ashamed" if future research overturns the conclusions? Huh? I thought that was the way science was supposed to work -- new data, different (sometimes improved) inferences.

Are the authors to be condemned for working in an area of science that folks, professional and nonpros alike, find interesting and exciting? Their paper was published merely to promote the authors' fame? They're somehow "selling" their science just because it makes a splash? Wow. And I though I was cynical.

Ken Weiss said...

We certainly differ about Nature. I don't think anything I've said criticizes the authors. Nor, I think, did Holly do that. We did not raise the kinds (and level) of criticism that has been raised.

As with other Nature covers we've criticized, it is the editors not the authors who are responsible, but they do set the nature and tone of the papers they publish.

Also, I think a few comments about this on our blog have asked why the paper wasn't more circumspect about findings and other possible interpretations. I can't judge that myself, obviously, but it has become a problem.

Perhaps, however, we simply differ on how things should be done to advance data, express opinions responsibly, discussion alternatives or do further testing, and, yes, shake the tree when it needs to be shaken (but not before that).

occamseraser said...

Ken --
Read the SOM. They were plenty circumspect wrt alternative explanations.

my bad -- erratum:
Marean's remarks were from NPR, not Nature:
"Curtis Marean (Marean) wrote:
DeGusta misrepresents the content of the paper when he states above that “And regardless, Dr. Alemseged and his colleague, they don't actually discuss the possibility of crocodile damage at all in their text. So to me that's a major oversight." On page 850 first paragraph in the main text of the published paper in Nature the authors state: “Finally, we used well known and described morphological criteria9,18,19,22–27 to distinguish between cut marks, percussion marks and tooth marks." Reference 22 is the Njau and Blumenschine paper in Journal of Human Evolution that describes crocodile tooth marks. Unfortunately errors such as this arise when scientists rush to the media to debunk claims by colleagues – perhaps that is what DeGusta may call “a major oversight".

The ASU press release does get a little breathless at points:
http://asunews.asu.edu/20100811_bones

WRT Nature, I've had mostly good experiences there, as an author and as a frequent reviewer. I usually get past the covers ;)

Ken Weiss said...

Well, Occam, your experience is reassuring. I read and subscribe, and have had a couple of things in there. But I won't back off complaining about the popularization of the leading journals, the temptation of authors to minimize caveats (they could, for example, have said
"listen, this is interesting but could be controversial. It's early evidence for a kind of tool use by hominins, but it's not the first use and could be interpreted in other ways. So don't play it up in the media."

Or, a responsible journal would not feel they have to sensationalize every finding. To me, and I realize this is just my view, we're in a crying-wolf era. Eventually science journals will return to a more sober, even boring, style that lets readers judge things without having to filter through hyperbole, whether by authors or the media.

Again, I certainly won't quibble with your experience or judgment!

Holly Dunsworth said...

For the record, I am not upset about the cover of Nature.

And as I mentioned above, yes they do cite the croc paper. That's not the only strange criticism out there either. Asking people to "see for themselves" photographic sims or diffs between McPherron's pics and Njau and Blumenschine is Mickey Mouse. No taphonomist would look at only photos and make conclusions.

And, yes, the SOM is a great read full of evaluation of criteria of alternative explanations. I do wish it was laid out more straightforwardly. Checking things off as you go, but then again, that's from a nonexpert who needs handholding through cutmark stuff.

In addition, I think that those parts, the testing of hypotheses, should be included in the full article (since they contain the actual scientific labor)!! To me, that's the meat and to Nature it's Supplemental.

Holly Dunsworth said...

@Ken. Ideally the evidence speaks for itself and no one has to judge anything ;).

Ken Weiss said...

Had Nature chosen the cover as they did, but the headline was

'Early evidence suggesting human tool use?'

I would have no reason to complain. I know from direct and nearly-direct experience the degree to which these journals (and I include Science) go for, or are almost restricting themselves to, things they can exaggerate.

Holly Dunsworth said...

My tongue in cheekness and playfulness doesn't come across as well as I'd like here (re: my ashamed comments above).

Holly Dunsworth said...

Perhaps part of the confusion is that Ken and I are having a playful conversation/debate publicly and we should be having it privately.

occamseraser said...

Have I mentioned how much I value the content of "the mermaid's tale"? I learn something every new post, even those I quibble with, and I apologize if I sometimes insert myself into the middle of what were intended as mostly personal exchanges.

I'm usually happy to see bioanthro and evobio of almost any variety featured in the commercial science news (and I love the immediate gratification of blogs), but I am also well aware of the nearly universal hyperbole and almost inevitable errors that go with popularizing and (over)simplifying a scientific finding. The one part of the scibiz that bothers me the most is the apparent need to amplify and sometimes even manufacture controversy (in the name of "balanced reporting", of course). I know for a fact that some science writers troll professional waters for negative commentary to spice up their "reports". Debate is almost always healthy, but the temptation (and opportunity) to say something provocative is sometimes just too great to resist.

To answer Holly's earlier question, I think the extra attention paleoanthro (whether fossils or genes) receives is mostly a good thing. Facts will be checked. Interpretations will be challenged and modified. Mistakes will be discovered and corrected. New methods will be developed or adapted. And new fossils/sequences will be found that start the cycle all over again.

Ken Weiss said...

We try very hard to make MT to be thoughtful and hopefully informative, if we have anything to say that others may not, given their particular circumstances and so on.

And, naturally, the very seriously substantial nature of the comments we get is extremely rewarding to us, and of course we gain selfishly by learning a lot from them.

The blogosphere can often just be a rant-o-sphere, which we try to avoid.

So thanks for your many contributions!

Holly Dunsworth said...

@occamseraser...*like*