Barbaric yawping about Neandertal women

This morning, my irritation level about this Neandertal women hunting story finally reached its boiling point. I unleashed a Neandertal-style cry of anguish -- which if you've never heard one, sounds remarkably like a Wookie-style cry of anguish.

Am I a simple misogynist? Does the idea of deerstalking Neandertal women threaten my manhood? Maybe, although Gretchen assures me I'm not. Mostly, I'm irritated because a full-text search of the paper yields no mention of any possible test of their idea.

I hate being so critical of this idea. I really like Kuhn's and Stiner's other work. But over half of people think that all our raving about ancient humans is fantasy anyway, so I try to be as critical as I can. And this is a real doozy.

It's bad enough for something like this to hit the New York Times. But this one has even invaded Instapundit. Clearly something must be done!

So, I told my class I was incapable of giving a normal lecture, and would continue on the subject of sexual division of labor until they found a satisfactory means of testing Kuhn and Stiner's hypothesis.

Unfortunately, my students actually like seeing me rant and tear out my hair, so they had a positive disincentive to find the right answer. So, if you want a job done right...

Testing the hypothesis

In case you've missed it, the proposition by Steven Kuhn and Mary Stiner -- excellent archaeologists, both -- is that Neandertal women were incapable of the kind of sex-based division of labor found in most human societies, and instead spent their time helping Neandertal men to find and kill large animal prey.

So let me approach this hypothesis with a skeptical eye. What exactly does it entail?

1. Kuhn and Stiner propose that modern humans had a fitness advantage because they mobilized female labor to find and process high-effort plant resources and small animals.

2. Neandertals were so committed to large-animal hunting that they required assistance from their women, compromising their ability to collect low-quality but dependable plant and small animal resources.

3. In Kuhn and Stiner's view, these differences meant that modern humans and Neandertals were locked onto different adaptive peaks, and Neandertals were constrained from adopting the modern human pattern of division of labor, even though it allowed greater population growth.

Why is the adaptive peak story (number 3) necessary? Here's why: if the behavior of Neandertal women was very flexible, then they could have adopted the broader dietary strategy easily. There would be no rugged fitness landscape, because behavioral plasticity would smooth the fitness differences.

In other words, condition (3) is absolutely necessary to the hypothesis that sexual division of labor was the fitness advantage of modern humans over Neandertals.

Testing the adaptive landscape condition

I think that the adaptive landscape assumption is the greatest flaw in this hypothesis. Kuhn and Stiner's hypothesis depends on the assumption that sexual division of labor is quite rigid, so that Neandertals did not adopt a modern organizational strategy even though such a strategy was adaptive for modern humans in the same habitat.

That is a very strong claim, but necessary to their hypothesis. If Neandertal social organization strategies were actually flexible, then cultural variation among Neandertal groups would have enabled some of them to find the high-fitness strategy. Once a few groups reached the high-fitness sexually divided labor strategy, they would have proliferated. That is precisely the logic behind Sewall Wright's shifting balance theory, and it applies here equally well. Plasticity enables a population to explore the fitness landscape.

So if Neandertal foraging behavior was actually flexible, then there would have been no impediment to Neandertal females exploiting collected plants and small animals. In fact, if you showed that Neandertals actually did collect plants and eat small animals, it seems to me that the entire argument about social organization is moot.

As noted in several of the comments on the Kuhn and Stiner paper, Neandertals did collect small animals, marine resources, and plants at many sites. They did use grinding stones occasionally in Eastern Europe. They did collect grass seeds in the Levant, and nuts in Spain. In other words, Neandertals did have substantial dietary flexibility. This evidence for flexibility is currently best outside northwestern and north-central Europe, at least from faunal and plant remains.

The flexibility is also evident in dental microwear, which includes individuals from northwest and north-central Europe (Pérez-Pérez et al. 2003, Lalueza 1996). Based on the dates of specimens with different wear patterns, Pérez-Pérez and colleagues suggested not only that Neandertals had great dietary flexibility, but also that they may have relied on plants more during colder climatic periods. Since the early Upper Paleolithic was one of the colder periods, this seems relevant to the apparent contrast in subsistence strategies. In any event, the idea that Neandertals were invariantly carnivorous is simply inconsistent with the pattern of data.

Let's consider for a moment what would cause Neandertals to continue to pursue a low-fitness hunting strategy when they obviously were capable of acquiring high-fitness plant foods, they experimented with high-fitness plant foods, and many of them ate enough of the high-fitness plant foods to mark up their teeth. It seems quite implausible that Neandertals were locked into a strategy of perpetual experimentation and sampling of a high-fitness resource!

I think we're forced to conclude that either (a) further exploitation of plant foods did not provide a high-fitness strategy, or (b) Neandertals were stupid. Right? All this rigmarole about organizational strategies becomes another way to describe Neandertal stupidity.

Human ecology

The best explanation for why Neandertals didn't use more plant foods is that they didn't pay. Here's what Kuhn and Stiner wrote about plant acquisition:

Vegetable foods may well have been part of Middle Paleolithic diets in Eurasia, but these were more like salads, snacks, and desserts than energy-rich staples. (Grinding stones are known from the contemporaneous Middle Stone Age in Africa, a point we will return to later.)
...Large underground storage organs are common among plant taxa in arid sub-Saharan Africa, but the high-yield edible plant foods of temperate and Mediterranean Eurasia tend to be seeds and nuts that, while potentially nutritious, require more effort to collect and process and thus afford low net yields (Kuhn and Stiner 2006:957).

So Neandertals were using the most energy-rich resource available in Europe, and this is a problem? Many of us like salads, snacks and desserts. If they were making effective use of the available plant foods, then there is no basis whatsoever to suggest that Upper Paleolithic people were pursuing a more effective strategy. As I hint below, Upper Paleolithic people and modern hunter-gatherers both may share demographic pressures that forced a reduction in diet quality and trophic level. We should attend to the ecological changes that made the Upper Paleolithic adaptation work.

The same argument applies to the changes in social ecology, including the use of needles in the Upper Paleolithic. As Soffer ably demonstrates elsewhere (with Adovasio and colleagues), Upper Paleolithic people used needles because they had fabric. Neandertals didn't. That was a technological innovation that changed human ecology.

Somebody might be tempted to say that if Neandertal women had adopted a fundamentally Upper Paleolithic social organization, they would have invented fabric. But that argument doesn't apply to any recent technological innovation (if only 1970's office workers had more time on their hands, they would have invented the spreadsheet!), so I don't see how it can sensibly apply to Neandertals.

The deerstalking women

Note that these observations say nothing about what Neandertal women actually did. In other words, we have shown that condition (3) is very unlikely, but we haven't addressed condition (2). Maybe, as part of their dietary flexibility, Neandertal women really did help with hunting some of the time.

At its boundary -- Neandertal women hunted occasionally -- this idea is nothing more than an untestable suggestion. We cannot negate such a broad suggestion. Besides, in broad form it is likely true. Who could deny that a hungry Neandertal woman might help her male groupmates drive animals into an ambush?

But I think we can at least test the idea that Neandertal women were habitual hunters. I am willing to make one assumption: Neandertal hunting strategies involved a higher mortality risk than Upper Paleolithic hunting strategies.

That assumption is justifiable in terms of technology -- Neandertals killed with close ambush methods because they did not have projectile weapons; Upper Paleolithic people did have projectile weapons, and they apparently also used more logistical hunting strategies. Also, the assumption is justifiable by mortality and injury data -- Neandertals died younger, and they died with lots of healed injuries.

Still, the mortality risk of Neandertal hunting was not uniformly distributed. Some roles were riskier than others. It may well have been that women could participate in hunting, as drivers for example, while bearing a lower mortality cost than men. This is, of course, a sexual division of labor, but such a division would not involve separate male and female collection strategies.

But if Neandertal women could bear a lower mortality cost while participating in hunting, then so could Upper Paleolithic women. And if Neandertal men could spend less time hunting and have a higher return rate with female help, then so could Upper Paleolithic men. And if Neandertal women didn't need to stay in camp to tend their children, then neither did Upper Paleolithic women.

In other words, if hunting was less risky for Neandertal women than for Neandertal men, it was even less risky for Upper Paleolithic women! Upper Paleolithic women should have been more likely to hunt than Neandertal women.

You see, the caloric return of different food sources (meat versus plants, big animals versus small animals) for Neandertals and Upper Paleolithic people would have been precisely the same, assuming the same success rate and risks. So to explain a difference between the two groups in adaptive terms, we need to posit a difference in their success rates or their risks.

We have four options:

a. Upper Paleolithic women achieved a higher return than Neandertal women from plants and small animals.

b. Upper Paleolithic hunting returns were much higher than Neandertal hunting returns, so women had plenty of free time to collect plants and small animals.

c. Upper Paleolithic hunting returns were much lower than Neandertal hunting returns, so women were forced to collect plants and small animals, despite their lower caloric value.

d. Upper Paleolithic camps were intrinsically more dangerous than Neandertal camps, requiring more women (and possibly men) to stay close to defend children and new mothers.

Each of these four options reduces to a very simple proposition. For example, under option (a), Upper Paleolithic women could have achieved higher return rates from plant foods if they had better technology. Option (b) implies that hunting technology increased Upper Paleolithic returns. Option (c) implies that demographic growth placed greater stress on local resources in the Upper Paleolithic (it is very similar to the "broad spectrum" idea as applied to the development of agriculture). And option (d) would imply that demographic growth resulted in more warfare between neighboring groups, also consistent with the increase in social markings and regional tool differentiation in the Upper Paleolithic.

Notice that all of these options come down to technological or demographic changes. None of them give an important causal role to sexual division of labor. Instead, the aspects of division of labor that can be observed in the archaeological record emerge as a result of basic technological or demographic conditions.

I view the demographic factors as more important than technological ones, but I have no strong rationale for this preference. To me, the most important point is that the risk factors constraining the adoption of full-time hunting for recent human women must have been even stronger for Neandertal women. This means if we want to find hunting women, we should look at recent human foragers. And they aren't there.

Technological or demographic conditions may have altered this picture, increasing the likelihood that Neandertal women did hunt. But there is no evidence that they did.

Final lessons

So the idea can be tested! It wasn't even that hard!

To the extent that we can compare with living and prehistoric humans, there is no support for the idea that Neandertals went extinct because their women spent too much time hunting. There are positive reasons that refute this idea -- most importantly, the demonstrated dietary flexibility of Neandertals and other archaic humans, which would have enabled Neandertal women to exploit a systematic plant and small animal collection strategy if it actually had increased their fitness. The fact that they did not do so is probably a reflection of their ecology, not their social organization.

It remains difficult or impossible to refute mere possibilities on the basis of the archaeological and fossil record. But we should remember that such mere possibilities are not testable hypotheses.

Certainly, some Neandertal women may have hunted along with Neandertal men. Maybe they were Neandertal Amazons who severed a breast to better thrust spears into roaming bison. After all, we know that they were capable of amputating limbs, so why not?

The "why not" in this case is, obviously, that Neandertal Amazons are a product of fantasy. Sure, the fossil record cannot rule out the possibility that they existed. But comparisons with our everyday experience and our knowledge of variation in other species both tend to indicate that such a curious adaptation would be unlikely.

The same is true of Kuhn and Stiner's model. A deerstalking Neandertal woman is by no means impossible. Maybe they spent a lot of time hunting, who knows? The problem is that there is no evidence that they did so.

References:

Bamforth DB. 2002. Evidence and metaphor in evolutionary archaeology. Am Antiq 67:435-452.

Kuhn SL, Stiner MC. 2006. What's a mother to do? The division of labor among Neandertals and modern humans in Eurasia. Curr Anthropol 47:953-980.

Lalueza C, Pérez-Pérez A, Turbon D. 1996. Dietary inferences through buccal microwear analysis of Middle and Upper Pleistocene human fossils. Am J Phys Anthropol 100:367-387.

Pérez-Pérez A, Bermúdez de Castro JM, Arsuaga JL. 1999. Nonocclusal dental microwear analysis of 300,000-year-old Homo heidelbergensis teeth from Sima de los Huesos (Sierra de Atapuerca, Spain). Am J Phys Anthropol 108:433-457. Abstract

Pérez-Pérez A, Espurz V, Bermúdez de Castro JM, de Lumley MA, Turbón D. 2003. Non-occlusal dental microwear variability in a sample of Middle and Late Pleistocene human populations from Europe and the Near East. J Hum Evol 44:497-513. DOI link