Andy White Anthropology
  • Home
  • Fake Hercules Swords
  • Research Interests
    • Complexity Science
    • Prehistoric Social Networks
    • Eastern Woodlands Prehistory
    • Ancient Giants
  • Blog

Paleoindian Population Dynamics Presentation (SEAC 2017) Available

11/11/2017

 
Today is my last morning in Tulsa at SEAC 2017. I spent all day yesterday in the "Paleoindian and Early Archaic Southeast" symposium: 18 papers that included state-by-state updates of what we know and the data we have and treatments of topics such as megafauna in the Southeast, plant use by early foragers in the region, wet site archaeology in Florida, lithic technologies, etc. It was a marathon. 

My presentation with David Anderson was last in the lineup. I was tasked with an effort at a "big picture" demography paper. It was a lot to talk about in a short time (20 minutes) -- a difficult balancing act to discuss the dense data from such a large area and be able to explain how I tried to integrate it all into a geographical/chronological model that can be evaluated on a region-by-region basis. Anyway . . . the detail will be there in the publications that result from the endeavor.

I uploaded a pdf of my presentation here. Some of the details will change as we work through the process of refining the analysis and dividing the content into multiple papers. But you should be able to get a decent idea of what we were going for. 
Picture

How Few Hunter-Gatherers is Too Few? Spoiler Alert: It's (Probably) a Lot Less than 500

9/19/2017

 
I'm happy to announce the publication of a new paper of mine in The Journal of Artificial Societies and Social Simulation (JASSS). JASSS is an open access journal focusing on the use of computer simulations as a tool for understanding social systems. I love publishing papers that anyone can get to at any time, without requiring logins, subscriptions, or fees. I wish every paper could be open access, and I wish I had the funds at my disposal to throw money at journals like JASSS to support such efforts. If I ever do have the money, that's the direction I'm going to throw it.

My paper, titled "A Model-Based Analysis of the Minimum Size of Demographically-Viable Hunter-Gatherer Populations" will appear in Volume 20, Issue 4 (due to be released on October 31). You can read the paper online here. It should be available in pdf form soon.

If you really want to get into the nitty gritty, the raw model code and an explanation are available here.
​
The focus of the paper using an agent-based model to revisit the question of how large human groups have to be to be demographically viable (i.e., able to survive over the course of many generations). This is a key question for understanding the size and structure of ethnographically- and archaeologically-known hunter-gatherer social systems as well as fleshing out scenarios of hunter-gatherer groups colonizing empty landscapes. Here is the abstract:

"A non-spatial agent-based model is used to explore how marriage behaviors and fertility affect the minimum population size required for hunter-gatherer systems to be demographically viable. The model incorporates representations of person- and household-level constraints and behaviors affecting marriage, reproduction, and mortality. Results suggest that, under a variety of circumstances, a stable population size of about 150 persons is demographically viable in the sense that it is largely immune from extinction through normal stochastic perturbations in mortality, fertility, and sex ratio. Less restrictive marriage rules enhance the viability of small populations by making it possible to capitalize on a greater proportion of the finite female reproductive span and compensate for random fluctuations in the balance of males and females."
Picture
My main finding is that, under the varying conditions I investigate with my model, I find no support for the often-repeated idea that a society of about 500 persons is required to ensure demographic viability.  Students of American anthropological archaeology -- especially, I suspect, those of us that went to the University of Michigan or were taught by U of M alums -- will immediately recognize the "magic number 500" as a concept that emerged from the research of Joseph Birdsell and (later) H. Martin Wobst. As I discuss in the paper, I think neither Birdsell nor Wobst intended the number 500 to take on the meaning that it did -- it became a kind of shorthand gloss for setting a general lower boundary on the size of hunter-gatherer social systems.

My modeling results suggest that the number of people required for demographic viability can be safely pushed down south of 200.  In over 67,000 model runs (under varying conditions of mortality, fertility, and marriage rules) where the mean population exceeded 150 people, the population went extinct only nine times.  I'd take those odds.

All the modeling was done under conditions with no logistical constraints to identifying and obtaining marriage partners:  no spatial component to interaction, no impediments to the flow of information. Logically, putting the model systems in space and dispersing the populations across a social/physical landscape would have the ultimate effect of raising the population size required for demographic viability. Would it double or triple it, though? I highly doubt it.  But the great thing about modeling is that we don't have to be satisfied to simply suppose things -- we can model the problem.  Understanding that less than 200 people are required for demographic viability assuming no interaction issues, we can then unpack the issue to ask why hunter-gatherer societies are often much larger. What role does the structure of mobility play? What about the need to maintain a geographically-extensive social fabric to buffer large-scale environmental variability? Here are a couple of paragraphs from my conclusion:
​
"My results are broadly consistent with those from two other models (Moore 2001 and Wobst 1974) that have considered questions of demographic viability and accord reasonably well with the empirical data we have that documents the existence of hunter-gatherer social systems appreciably smaller than 500 persons (see Birdsell 1953, Figure 9; Moffett 2013). Factors other than stochasticity in mortality, fertility, and sex ratio (e.g., environmental variability of spatial components of interaction behaviors) presumably influence the size of actual hunter-gatherer social systems and encourage them to exceed the minimum size threshold required for demographic viability. If we accept that a population of 150 is a reasonable baseline estimate for the population size sufficient to ensure demographic viability over long spans of time, we might then reasonably reconsider our explanations for why some hunter-gatherer social systems exceed this minimum. If there is a downward pressure that encourages hunter-gatherer social systems to be as small as possible, it seems likely that something other than demographic viability (in the sense of the term as used here) constitutes the limiting factor when social systems encompass significantly more than 150 people. Understanding how other factors might relate to the minimum and maximum size of hunter-gatherer populations will require further work."
Picture

Three for Thursday: Demography, Swords, and Trophy Bases

3/16/2017

 
Following the spring break hiatus, the Broad River Field School will be back in session tomorrow. We'll be shifting gears a bit to carefully work our way into what appears to be a buried Late Archaic/Early Woodland component. I'm also anticipating continued work on the deeper deposits at the site. Hopefully it will be an eventful day. It's supposed to be sunny and in the mid 60's. I'll just leave it at that.

Here are a few quick updates on other things for those playing along at home: a new modeling paper about the minimum size of demographically viable hunter-gatherer populations, new Fake Hercules Swords en route, and an identification of last Friday's whatzit. 

Picture
How Small is Too Small?

I'm happy to announce that a paper I submitted to the Journal of Artificial Societies and Social Simulation (JASSS) has been accepted for publication.  The paper ("A Model-Based Analysis of the Minimum Size of Demographically-Viable Hunter-Gatherer Populations") uses computational modeling to systematically investigate how large hunter-gatherer populations have to be to survive over long periods of time. Spoiler alert: my results suggest that populations much smaller than the "magic number" of 500 are demographically viable over several centuries under the conditions I explore with my model (in this case, FN3D_V3). JASSS is open access. I'll let you know when the paper becomes available.

Picture
Two New Swords on the Way

Two new Fake Hercules Swords should arrive at my office any day now. Alert #Swordgate enthusiast Hartman Krug spotted these swords, which are currently being produced in Italy. Because the company doesn't ship to the U.S., I asked a relative in Germany to purchase them for me and ship them to South Carolina. After arriving in New Jersey a few days ago, they are currently listed by the USPS as "in transit to destination."

It will be really interesting to have a look at this and delve into the history of the company making them. Could this finally lead us back to the original Mother of All Fake Hercules Swords?

The purchase and shipping of these swords was supported by your contributions to Woo War One. There's still a positive balance there, but it's dwindling. If you'd like to help keep the pressure on and get to the bottom of this, please consider contributing.

Picture
The Whatzit: A Trophy Base?

The "what the heck is this" post I put up last Friday was fun. Within a few minutes of asking the question to an artifact group on Facebook, someone suggested that the item is a base for a trophy. That explanation made sense to me (you can see some new ones for sale here).

Following the post, the owner of the artifact told me he returned to the same creek where he found the original artifact and found another one (left) that lacks the rounded corners of the first one (right). What these things are doing in a creek in Tennessee I do not know.

If you've got a whatzit, send me some photos and maybe we can get it figured out.

Finally, following up on yesterday's post about Against Me!, I would like to encourage you to listen to the song "Rebecca" if you like the rock'n'roll music. It's on repeat in Andyland. 

Repast Simphony Batch Runs: Note to Self

2/15/2017

 
I've found that the notes I make on my website are much easier for me to find later than the things I scrawl on pieces of scrap paper. The shoe fits, so I'm going to wear it whether or not it's interesting or useful to anyone else.

I've spend much of my time since Monday working to get the agent-based model I'm currently messing around with (version 3 of ForagerNet3_Demography) to work in version 2.4 of Repast Simphony. Something went awry with my previous installation (2.0) and it made sense to start trying to fix things with the most current version. After many frustrating loops of install/uninstall/reinstall, I finally got a good installation of 2.4 and got my source files moved in and working.

One thing that I wasn't able to make functional in the last version was the batch mode.  Batch mode lets you run jobs in batches, speeding up computation by farming out the computational workload to different processors or machines, etc. (doing runs in parallel rather than serial). It wasn't too troublesome that I couldn't get the embedded batch mode working before, as the model I'm working with isn't terribly demanding. There are bigger things coming down the road, however, so I was happy to see the batch mode appeared to be active and ready to go with the new installation.

I spent most of yesterday trying to figure out how to use the batch mode while preserving the data output format that I've created on my own and that works for me. The way I've written the model, it produces a summary data file at the end of each run. The file (just a simple .txt file that I can open in a spreadsheet) preserves information on all the parameter settings used in the run as well as data on the outcomes. In the Repast/Eclipse batch mode, however, that .txt file wasn't getting produced. I was frustrated to learn that I apparently had to redo all the data capturing in the model so that the software could use something called a "file sink" to collect information. I was then relieved to learn that there was a workaround to using the "embedded system:" you can specify an "Optional Output File Pattern:"
Picture
The "Pattern" is the name of the file produced by the model. I changed the file name to "TestBatchMode.txt" in my code for the purposes of experimenting with where and under what circumstances the file would be created. The "Local Path" is what you want the file to be called that the batch mode creates (it will appear in the output directory specified above). Check the "Aggregate" box so that it saves the output from each run and then gloms it all together in a single file. I left "Has Header" unchecked because my data doesn't have a header.

Repast seems to be picky about the settings in the "batch_params.xml" and "parameters.xml" files, wanting them to match. I get null pointer exceptions when I clear everything but the random seed out of the files, so I just left a parameter in to keep the software happy (it does nothing, as it's a constant and doesn't affect any of the settings in the model). 

I'm still testing out the batch mode and the model to make sure everything is working properly. My plan then is to modify version 3 to create version 4, which will include some different mortality settings (which, in turn, will necessitate rewriting some of the code that calculates age-specific mortality outcomes). After all that's done, I'm planning on doing some new modeling work to formally follow up on some preliminary observations I presented at the SAA meetings a few years ago.

ForagerNet3_Demography (Version 3): Description and Code Available

11/29/2016

 
Picture
I devoted yesterday afternoon and most of today to (finally) producing the updated documentation for Version 3 of the ForagerNet3_Demography model, one of the agent-based models that I've been working with. You can read all about it on this page, and you can even download the raw code if you like. Files and citation information for the model are also available on OpenABM.org.

I used a version of this model (implemented in Repast J rather than Repast Simphony) in a recent paper published in Uncertainty and Sensitivity Analysis in Archaeological Computational Modeling (edited by Marieka Brouwer Burg, Hans Peeters, and William Lovis).

Over the summer I used to model to generate data for a paper on the minimum viable population (MVP) size of human groups. That's in the editing stages now -- hopefully I'll be able to get it done and submitted somewhere before the Christmas break.

​Onward.

The Dependency Ratio in Human Evolution

5/15/2015

 
As far as I know, humans are unique among animals in having an extended period between weaning and being able to subsist on their own.  We call this “childhood.”  The long period of post-weaning dependence provides our large brains with a lot of time to mature.  It also requires a lot of parental investment (in terms of time, energy, calories, etc.) and means that we would have to wait a long time between offspring if each one had to independent before the mother could have another.   We don’t do that, tending to have a shorter interval between subsequent births (the inter-birth interval, or IBI) than other great apes.  The long period of childhood dependence and the short IBI mean that, as a species, humans tend to have multiple, dependent offspring of different ages at the same time.  Speaking as a parent of multiple, dependent offspring of different ages, I can tell you that this is often no walk in the park.  This peculiar human strategy has a lot of costs.

Understanding when, how, and why this distinctly human reproductive strategy developed is a great evolutionary question.  Reducing the IBI increases the potential fertility of human populations, but also creates new demands on the energies of parents and families.  Human families today often offset those extra energy demands by getting help (evolutionary anthropologists call it “cooperative breeding”).  A new paper in the Journal of Human Evolution titled “When Mothers Need Others” by Karen Kramer and Erik
Otárola-Castillo tries to further our understanding of where cooperative breeding comes from, using an “exploratory model” to try to understand the selective pressures associated with the evolution of human-like patterns of reproduction and child-rearing.  The goal of the paper “is to develop a model to predict those life history transitions where selective pressure would have been strongest for cooperative childrearing” (pg. 5). 

Kramer and
Otárola-Castillo call their model the “Force of Dependence Model.”  Their model is a simple one, calculating “the net cost of offspring as a function of dispersal age, birth intervals and juvenile dependence” as a 3-dimensional surface (Supplementary Online Material  from Kramer and Otárola-Castillo 2015).  The authors use several different combinations of settings to represent a range of conditions from “ancestral” (juvenile independence at age 10, IBI of 6 years, and a dispersal age of 14) to “most derived” (juvenile independence at age 20, IBI of 3 years, and a dispersal age of 20).  Their graphs show that “net costs” within a domestic group (a mother and her offspring) are lower when offspring are spaced further apart and become independent at a younger age.  When offspring hang around past the age of juvenile independence, there is a net benefit to the domestic group as their productive capacities can be used to offset the drain of their younger siblings. The authors find that the strain points – where selective pressures for assistance would be greatest – occur in domestic groups with the most derived set of characteristics: late juvenile independence and a low IBI (lots of children who remain dependent for a long time).   

As I understand it, the “net cost” in this model more-or-less mirrors the dependency ratio (the ratio of consumers to producers) of a domestic group or family, something anthropologists have been interested in understanding for a long time.  The higher the ratio of consumers to producers, the higher the dependency ratio, and the higher the “cost” to each producer supporting the family.  The dependency ratio changes through the lifespan of a family in a patterned way: every domestic group that has children goes through a “pinch” period when the dependency ratio is highest, and the pinch period logically corresponds to the time when there are a lot of dependent offspring.  As I wrote in my 2013 paper in the Journal of Anthropological Archaeology (“Subsistence Economics, Family Size, and the Emergence of Social Complexity in Hunter-Gatherer Systems in Eastern North America,” available here):

“the duration and amplitude of the ‘pinch’ is affected by the rapidity of the addition of offspring and how quickly those offspring turn from consumers into producers.  The rapidity of addition of offspring will depend on factors such as fertility, infant and childhood mortality, and the number of wives. The productive potential of children will be affected by the presence and distribution of resources that can be procured by children and the foraging strategies that are employed to exploit those resources” (White 2013:128).

The main part of that paper used an agent-based model (ABM) to try to understand how the distribution of family size changes when the age at which children become producers (the “age of juvenile independence” in Kramer and
Otárola-Castillo’s model) decreases and there is an incentive for polygynous marriage.  In addition to the ABM, I used a simple spreadsheet model to show how the dependency ratio changed through the course of the developmental cycle of an individual family in cases where the age at production was low (8 years old) and where it was high (14 years old).  In this simple model, I used an IBI of 3, a dispersal age of 16 for females and 20 for males, and a female reproductive period spanning ages 20-35 years (giving a total fertility of 6 offspring).

The figure below compares Kramer and
Otárola-Castillo’s graphs from their cases with early and late juvenile independence (holding IBI at 3 and dispersal age at 14) with my data on changes in dependency ratio through the developmental cycle in cases with a single reproducing female and an age at production of 8 (top) and 14 (bottom).   My model data are the same as in my 2013 paper (Figure 5), but I have re-graphed them to make comparison with Kramer and Otárola-Castillo’s figure easier.  I have redrawn the graphs from Kramer and Otárola’s Figure 1 (third graphs from the left, top and bottom rows).   The dotted lines on the graphs of my results indicate a dependency ratio of 1.75, which is what I have generally used in my modeling efforts as a “typical” dependency ratio among hunter-gatherers (following Binford 2001:230).
Picture

My results showed the same pattern as Kramer and Otárola-Castillo’s:  the peak of the “pinch” comes earlier and is less severe when children become producers at an earlier age.  Even though our models have some differences (and some of the values of the parameters were different), the correspondence in results is notable. Compare, for example, when the amplitude of the “pinch” (peak dependency ratio in my results, greatest net cost in Kramer and Otárola-Castillo’s results; marked by stars) is greatest and the differences in amplitude between the early and late ages of juvenile contributions to subsistence.

The correspondence between my results and Kramer and
Otárola-Castillo’s is unsurprising.  The idea that the dependency ratio of a domestic group changes through the course of its developmental cycle in a somewhat predictable way is not new (and the idea that the “pinch” comes when you have lots of little kids running around at the same time won’t come as a revelation to anyone who has multiple children).   This is a phenomenon that has been studied for decades (e.g., Chayanov 1966; Donham 1999; Fortes 1958; Goody 1958) and recognized as a key aspect of how hunter-gatherers organize themselves (Binford 2001:229).

So where does this kind of work put us in terms of understanding the evolution of human reproduction, society, and family life?  I think it primarily puts us in a spot where we’re asking some good questions.  Going back to the issue of the origins of monogamous pair-bonding (which I touched on briefly in this post about birth assistance and this post about australopithecine sexual dimorphism), having a two person (male-female) unit forming the core of a domestic group would have a mitigating effect on the strain caused by a decrease in IBI (i.e., you’d be adding another producer into the equation).  If the appearance of male-female pair-bonding was associated with a sexual division of labor (which is I think what most of us would hypothesize), males and females would presumably be focused on procuring somewhat different sets of subsistence resources.  Offspring could be largely “independent” with regards to some of those resources but not to others – think about the difference between collecting berries and running down large game.  A sexual division of labor and an environment where relatively young children could make some contribution to their own subsistence (even if that contribution does not include the full range of resources that are exploited) would go a long way toward easing the “pinch” that comes from having more children spaced closer together.

When does this happen in human evolution?  Of course that’s a tough thing to get at directly.  I think if you took a poll, the winner would probably be “around the time our genus emerges” or “with Homo erectus.”  An increase in total fertility (coincident with a lowering of the IBI) would help explain the population growth that must have been part of the dispersal of our species out of Africa prior to 1.8 million years ago.  It would also fit nicely with the evidence for an increased exploitation of animal resources around that same time.  Maybe Glynn Isaac was right all along to propose the emergence of human-like central place foraging with home bases and a sexual division of labor at the beginning of the Lower Paleolithic?

But what if monogamous pair-bonding and a sexual division of labor appeared much earlier – with australopithecines or even some pre-australopithecine like Ardipithecus?  If those things came along with bipedal locomotion, would a decreased IBI and increased fertility have followed automatically?  Maybe not.  Perhaps those earlier hominids just didn’t have the wherewithal to exploit their environments like later hominids did – perhaps the diversity of the resource base they could exploit wasn’t great enough to really leverage a sexual division of labor until animal products became readily attainable.  That may have required a suite of anatomical adaptations for daytime exhaustion hunting (loss of body hair, skin pigmentation, greater body size, stiffer foot) and cognitive/behavioral adaptations for making and using stone tools to process carcasses.  The date of the “earliest” proposed use of stone tools continues to be pushed  back (now it’s at 3.3. million years ago), but as far as I know the density of stone tools and butchered animal bones that appears at about 1.8 million years ago is unlike anything that precedes it.

More modeling work will be required to really understand how changes in the dependency ratio might have articulated with changes in reproductive, social, and technological behaviors deep in human prehistory.  In order to understand what changes in reproduction might have meant in terms of social interactions, however, we’ll need a different grade of model than that used by Kramer and
Otárola-Castillo.  Of course I’m going to say that complex systems modeling is the way to go on this:  it will let us get past the limitations of deterministic inputs and help us understand how constraints, costs, and interactions would have played out within a society.   In order for “others” to help with raising and provisioning multiple dependents, those others had to have existed within these small-scale hominid societies and (again, speaking as someone involved in raising multiple small kids) there wouldn't have been some inexhaustible Plio-Pleistocene babysitting pool of “others” out there just waiting to step in and provide extra calories for a few years.  A different kind of modeling effort with broader scope will let us get at the group- and society-level contexts in which family-level changes in child-bearing and child-rearing would have played out. Stay tuned.
References

Binford, Lewis R.  2001. Constructing Frames of Reference: An Analytical Method for Archaeological Theory Building Using Hunter-Gatherer and Environmental Data Sets.  University of California Press, Berkeley.

Chayanov, A. V.  1966.  A. V. Chayanov on the Theory of Peasant Economy.  University of Wisconsin Press, Madison.

Donham, Donald L. 1999.  History, power, ideology: Central issues in Marxism and anthropology.  University of California Press, Berkeley.

Fortes, Meyer.  1958.  Introduction.  In The Developmental Cycle in Domestic Groups, edited by Jack Goody, pp. 1-14.  Cambridge Papers in Social Anthropology.  Cambridge University Press, London.

Goody, Jack.  1958.  The Fission of Domestic Groups among the LoDagaba.  In The Developmental Cycle in Domestic Groups, edited by Jack Goody, pp. 53-91.  Cambridge Papers in Social Anthropology.  Cambridge University Press, London.
ResearchBlogging.org
Kramer, K., & Otárola-Castillo, E. (2015). When mothers need others: The impact of hominin life history evolution on cooperative breeding Journal of Human Evolution DOI: 10.1016/j.jhevol.2015.01.009

Fetal Head Molding and Obstetrics in Late Pleistocene Humans

3/15/2015

 
Preface: This post presents some work I did as a graduate student at the University of Michigan in 2007.  It was a poster for a class called "Evolution of the Genus Homo," taught by Milford Wolpoff.  I chose the topic because of my interest in the culture, biology, and social organization of Middle/Late Paleolithic humans (see discussion of my 2014 SAA paper here and here, and my 2015 AJPA paper here).  I had hoped to develop this into a paper either alone or with a collaborator, but I have never found the time to follow through.  As the information I collected ages and I begin to focus on moving to a new job that will require a lot of attention up front to the archaeology of the southeastern United States, it seems less and less likely that I'll ever get around to turning this into a paper. So I'm going to put my analysis from the poster out there "as is" and hope it useful to someone.  If you read this and think it's an interesting idea or one that you'd like to pursue, let me know!

I apologize for the state of the bibliography: there are some formatting errors that I will correct when I have the time.


Fetal Head Molding and Obstetrics in Late Pleistocene Humans
PictureFigure 1. Illustration of changes in head shape that occur during birth (from A.D.A.M).
Introduction

This study compares available data from fetal and neonatal crania from the Late Pleistocene to the mechanics of fetal head molding during birth in recent humans.   The small number of fetal and neonatal remains dating to the Late Pleistocene offer an opportunity to simultaneously explore issues of obstetrics, selection, and early brain growth.  Most treatments of birth and obstetrics in Pleistocene humans have focused on pelvic anatomy (e.g., Rak and Arensburg 1987; Rosenberg 1998; Rosenberg and Trevathan 2002; Trinkhaus 1984).  Studies of childhood growth and development after birth are limited mainly by the dearth of sub-adult skeletons, particularly those that pre-date Neandertals (see Anton 2002; Dean et al. 1986; Minugh-Purvis 1988, 2002; Nelson and Thompson 2002; Stringer et al. 1990; Tellier 1998; Trinkhaus and Tompkins 1990).   Fetal and neonatal remains, from Neandertals and other Late Pleistocene humans, have been described but have not been the subject of detailed, hypothesis-based research.
 
Deformation (molding) of the fetal cranium is an important part of successful birth in recent humans.  This study examines the hypothesis that thickness of fetal cranial bone would have been an impediment to successful birth in Neandertals and other Late Pleistocene humans.  Investigating the possible role of fetal head molding in Pleistocene obstetrics may help shed light on both anatomical trends in human cranium (i.e., the emergence of "modern" cranial morphology) and demographic variables and population genetics that may underlay the spread of anatomical "modernity."   Mortality and trauma during childbirth, acting on the mother and/or the fetus, would be an important selective force.

Two aspects of fetal head molding are emphasized: cranial vault thickness and head dimensions.    Vault thickness affects the response of the cranium to pressure during birth.  Head size and shape affect both the degree of molding that is required for the fetal head to pass through the birth canal and the distribution of forces on the fetal cranium.

Hypothesis:  Thick fetal cranial bone in Late Pleistocene archaic humans would have caused difficulties during childbirth (relative to recent humans) by inhibiting head molding during delivery.

Assuming uniformity in the size of the birth canal between archaic and recent humans, this hypothesis has two test implications:

1) the increased thickness of Late Pleistocene fetal cranial vaults would have a significant effect on elasticity of the cranium

2) the dimensions of the fetal cranium are such that significant molding is required for delivery

In other words, fetal head molding must be shown to be both necessary (by the dimensions of the cranium) and significantly impeded (by the in-elasticity of the vault) in order to fail to reject the hypothesis.  If either one of these test implications is rejected, then the hypothesis can be rejected.


Pleistocene Obstetrics: Previous Research

Much research focused on questions of obstetrics in Pleistocene humans have emphasized the selective constraints between locomation and birth mechanics in the pelvis (Rak and Arensburg 1987; Rosenberg 1998; Rosenberg and Trevathan 2002; Ruff 1995; Trinkhaus 1984).  Based on pelvis remains, most researchers conclude that birth in Pleistocene humans was much like birth in recent humans (Rosenberg 1998; Rosenberg and Trevathan 2002).  Subsequent to the description of the Kebara 2 pelvis (Rak and Arensburg 1987), most ideas about an unusually long gestation periods (Trinkhaus 1984) and rapid in utero brain growth (Dean et al. 1986) in Neandertals have been rejected (see Stringer et al. 1990:148).
 
While pelvic inlet size during the Pleistocene appears to be, overall, similar to modern humans, cranial capacity increased. during the Middle and Late Pleistocene.  Stasis in pelvic inlet size and increase in head size produces an "obstetric dilemma" where the fetal head is larger than the birth canal.  Rosenberg and Trevathan (2002:1205) state that

"Two changes could have allowed an increase in adult brain size to occur: human infants could have been born with a smaller percentage of adult brain size (resulting in greater infant helplessness) and/or there could have been an alteration of the shape of the pelvis concomitant with a change in the mechanism of birth."

There is a third possibility:  fetal head molding.  The possible importance of fetal head molding in Neandertals is raised by similarities in both pelvic inlet size and adult cranial capacity to recent humans.  Minugh-Purvis (1988:260) speculated that the thicker vault bone observed in Neandertal fetal remains would have posed a problem if delivery required a "considerable degree of head molding."  The possibility was also discussed by Friedlander and Jorndan (1994).

PictureFigure 2.
Fetal Head Molding in Recent Human Birth

In recent humans, the fetal cranium is a flexible structure that deforms during birth because of pressures between the fetal head and the cervical walls (Lapeer and Prager 2001; McPherson and Kriewall 1980a, 1980b) (Figure 2).  Pressures and deformation are greatest at the sub-occipito bregmatic plane (Lapeer and Prager 2001;  Rosenberg and Trevthan 2002).  

During a normal labor, the parietal bones undergo the most significant changes in shape, being compressed towards each other and elongating in the axial plane (Lapeer and Prager 2001; McPherson and Kriewall 1980b).  The occipital bone is relatively rigid and undergoes little change during molding (McPherson and Kriewall 1980b:18; Rosenberg and Trevathan 2002:1201).  The frontal, occipital, and parietal bones interlock at the sutures after a certain limit of deformation occurs, preventing excessive molding and protecting the brain within a more rigid structure (McPherson and Kriewall 1980a:15).  

The risk of excessive molding is greater in pre-term deliveries, where cranial bone is not sufficiently thick to prevent excessive molding (McPherson and Kriewall 1980a). Clinical studies have shown that excessive molding during birth (i.e., where too much deformation occurs) may be linked to psycho-neurological disorders, mental retardation, cerebral palsy, and death (see McPherson and Kriewall 1980b).

Fetal cranial bone must be thin enough to allow sufficient deformation of the cranium, but thick enough to form a rigid structure to protect the brain.  Optimal thickness values would vary for different portions of the fetal cranium depending on the pressures that are exerted and the required responses to those pressures.


Parietal Thickness, Span, and Deformation Under Load

Parietal bones grow outward from a center of ossification that later becomes the parietal eminence (Ohtsuki 1980).  The bones are thickest at the eminence, thinning towards their margins (McPherson and Kriewall 1980b).  Ohtsuki (1977) reported a mean thickness of 0.54 +/- 0.13 mm for term (9-10 month) fetal parietal bones at the center of ossification and a thickness of 0.40 +/- 0.10 for term fetal frontal bones at the center of ossification (n = 10).  McPherson and Kriewall (1980a:10) reported term fetal parietal bones that varied in mean thickness from 0.71-0.86 mm.

In their analysis of the mechanical properties of fetal parietal bone, McPherson and Kriewall (1980a:11) found that differences in thickness and the orientation of the bone fibers affected the elastic modulus (the resistance to deformation when a load is applied).  Thicker cranial bone requires more force to deform.  Figure 3 shows the relationship between thickness and elastic modulus in the data supplied by McPherson and Kriewall (1980a:10,13), using only the parietal bones with fibers orientated parallel.

Using the formulae provided by McPherson and Kriewall (1980:11), we can use the estimates of elastic modulus to estimate the loads that would be required to bend segments of bone of varying length and thicknesses (Figures 4 and 5).  Other things being equal, longer "beams" of bone require less force to bend, while thicker "beams" require more.  To have the same resistance to bending force, a longer "beam" must be thicker.
Picture
Figure 3. Thickness of fetal cranial bone plotted against elastic modulus (data from McPherson and Kriewall 1980a). The regression (R2 = 0.78) is: 4.13 + 2.86(log of thickness in mm)
Picture
Figure 4. Plot of force required to cause a deflection of 1 mm in "beams" of bone of varying thickness (assuming a beam length of 75 mm - approximately that of a modern human term fetus). While the absolute values of these calculations may not be accurate (parietal bones vary in thickness in cross-section and do not behave simply as "beams") the calculations show that the resistance to force changes dramatically when thickness increases from 1 mm to 2 mm.
Picture
Figure 5. Plot of force required to cause a deflection of 1 mm in "beams" of bone of varying length (assuming a beam thickness of 1 mm).

Fetal Vault Thickness, Dimensions, and Molding in Late Pleistocene Homo

The Late Pleistocene fossil record contains numerous remains from sub-adult specimens.  Of interest here are those remains that preserve portions of the cranial vault, particularly the frontal and parietal bones.  Fetal and neonatal remains of Neandertals have been recovered from La Ferrassie (Heim 1982) and Hortus (Lumley-Woodyear 1973).  Rremains of two Neandertals less than about a year old have been reported from Shanidar (Trinkhaus 1983) and Krapina (Minugh-Purvis 1988).  Neonatal remains attributed to anatomically modern Homo sapiens have been reported from Cro-Magnon (Minugh-Purvis 1988), Qafzeh (Tillier 1999), and Abri Patuad (Minugh-Purvis 1988).  Krapina is the earliest site, dating to the late Riss/early Wurm (Wolpoff 1999).  La Ferrassie, Shanidar, Qafzeh, and Hortus date to Wurm I/Wurm II.  Abri Pataud and Cro-Magnon date to Wurm III/IV (Wolpoff 1999).
Vault Thickness

Data on vault thickness at the parietal and frontal eminences are available for six fetal/neonate skeletons and three young (<1 year) infants from the Late Pleistocene. 
Picture
Picture
Figure 6. Top: Drawing of Neandertal neonatal parietal from Hortus 1b (adapted from Lumley-Woodyear 1973). Bottom: Neandertal fetal and newborn frontal bone fragments from La Ferrassie compared to frontals from recent humans (adapted from Heim 1982).
PictureFigure 7.
The thickness of the frontal and parietal bones in this sample contrasts with the data from the modern sample provided by Ohtsuki (1977) (Figure 7), outside the 2 sigma range of his means for term fetuses.   If the Late Pleistocene fetal and neonate remains are aged accurately, fetal parietal bone was generally 1.5 to 2 times thicker than that of modern humans.  

Considerably more  force would be required to deform these bones, assuming the geometry of the bones was otherwise equivalent (see below). 

Test prediction 1 is supported: differences in fetal cranial vault thickness are sufficient to affect molding of the cranium.

Fetal Head Dimensions

The limited data available on very young Late Pleistocene individuals suggests that some aspects of fetal head geometry may have differed from that of more recent humans (Minugh-Purvis 2002; Stringer et al. 1990).  Bregma-lambda distance appears to have been shorter in Neandertals than in recent humans throughout life (see Minugh-Purvis 2002:488-489; Gunz and Havarti 2007; Harvarti 2003; Trinkhaus 1983:371).  In mature Neandertals, the shorter distance is associated with a lower position of bregma (see Harvarti 2003) 
Picture
Figure 8.
A shorter bregma-lambda distance would reduce the cross-section of the fetal cranium in a dimension that is key to the necessity for fetal head molding.  It appears that this distance may have been about 10 mm less in Neandertals at the time of birth relative to recent humans: perhaps 80 mm rather than 90 mm (see Minugh-Purvis 2002).  A difference of ca. 10-12% in the bregma-lambda chord would be sufficient to account for a 3-7% reduction in the sub-occipito-bregmatic diameter (SOBD).  Assuming equivalence in other dimensions of the head and pelvic inlet, this difference alone would significantly lessen the degree of fetal head molding that would be required for successful delivery. 

Test prediction 2 is not supported: the dimensions of the fetal cranium are such that significant molding was probably not required for delivery.

Conclusions

Significant fetal head molding was probably not critical to successful Neanderthal birth.   While thicker cranial bone would have reduced elasticity, a smaller SOBD would have negated or lessened the need for molding during birth.  

Reduction in fetal cranial thickness may not have been a reproductive advantage for "modern" humans.  Rather, cranial thinness associated with an increase in the SOBD may have increased the risks to the fetus during birth (i.e., though excessive molding) while reducing or maintaining the risk to both mother and fetus (i.e., through arrested labor).  In the absence of selection for thinner bone associated with a flexibility requirement, thick fetal cranial bone would have offered protection to the fetal brain during delivery.  Apparent stasis in pelvic anatomy suggests that smaller, thicker fetal crania may be the ancestral condition.  An increase in SOBD, perhaps reflecting some difference in fetal brain growth,  would have preceded selection for thinner cranial bone in this scenario.  

The fetal cranium is a complex mechanical structure.  Constructing a simulation model (similar to that of Lapeer and Prager 2001) of delivery in Neanderthals is possible with the available data.  This model could be used to test hypotheses about obstetrics in a more sophisticated way than is possible by calculating simple ratios of head and pelvic size.

References Cited
Anton, Susan C. 2002.  Cranial growth in Homo erectus.  In Human evolution through developmental change, edited by Nancy Minugh-Purvis and Kenneth J. McNamara, pp. 349-380.  Baltimore: Johns Hopkins University Press.

Dean, M.C., C. B. Stringer, and T. Bromage. 1986.    Age at death of the Neanderthal child from Devil’s Tower, Gibraltar and the implications for studies of general growth and development in Neanderthals.  American Journal of Physical Anthropology 70:301-309.

Friedlander, N. J., and D. K. Jordan. 1994. Obstetric implications of Neanderthal robusticity and bone density.  Human Evolution 9:331-342.

Gunz, Philipp, and Katerina Havarti. 2007.   The Neanderthal “chignon”: Variation, integration, and homology.  Journal of Human Evolution 52:262-274.

Havarti, Katerina. 2003. The Neanderthal taxonomic position: Models of intra- and inter-specific craniofacial variation.  Journal of Human Evolution 44:107-132.

Heim, Jean-Louis. 1982.  Les enfants nJandertaliens de La Ferrassie.  Paris, Masson.

Lapeer, R.J., and R.W. Prager.  2001. Fetal head moulding: Finite element analysis of a fetal skull subjected to uterine pressures during the first stage of labour.  Journal of Biomechanics 34:1125-1133.

Lumley-Woodyear, Marie-Antionette de. 1973.    AntenJanderthaliens et NJandertaliens du bassin Mediterraneen occidental europen.  Etudes Quaternaires.  MJmoire 2, Marseille, UniversitJ de Provence.

McPherson, Gregg K., and Timothy J. Kriewall. 1980a.  The elastic modulus of fetal cranial bone: A first step towards an understanding of the biomechanics of fetal head molding.  Journal of Biomechanics 13:9-16.

McPherson, Gregg K., and Timothy J. Kriewall. 1980b.  Fetal head molding: An investigation utilizing a finite element model of the fetal parietal bone.  Journal of Biomechanics 13(1):17-26.

Minugh-Purvis, Nancy. 1988.  Patterns of craniofacial growth and development in Upper Pleistocene hominids.  PhD dissertation, University of Pennsylvania.

Minugh-Purvis, Nancy. 2002.    Heterochronic change in the neurocranium and the emergence of modern humans.  In Human evolution through developmental change, edited by Nancy Minugh-Purvis and Kenneth J. McNamara, pp. 479-498.  Baltimore: Johns Hopkins University Press.

Nelson, Andrew J., and Jennifer L. Thompson.  2002.   Adolescent postcranial growth in Homo neanderthalensis.  In Human evolution through developmental change, edited by Nancy Minugh-Purvis and Kenneth J. McNamara, pp. 442-463.  Baltimore: Johns Hopkins University Press.

Ohtsuki, Fumio. 1977.    Developmental changes of the cranial bone thickness in the human fetal period.  American Journal of Physical Anthropology 46:141-154.

Rak, Y., and B. Arensburg. 1987.    Kebara 2 Neandertal pelvis: First look at a complete inlet.  American Journal of Physical Anthropology 73:227-231.

Roche, A. F. 1953.    Increase in cranial thickness during growth.  Human Biology 25(2):81-92.

Rosenberg, Karen R.  1992.   The evolution of modern human childbirth.  Yearbook of Physical Anthropology 35:89-124
 

Rosenberg, Karen R. 1998.  Morphological variation in west Asian postcrania.  In Neandertals and modern humans in western Asia, edited by Takeru Akazawa, Kenichi Aoki, and Ofer Bar-Yosef, pp. 367-379.  Plenum, New York.

Rosenberg, Karen, and Wenda Trevathan. 2002.    Birth, obstetrics and human evolution.  BJOG: an International Journal of Obstetrics and Gynaecology 109:1199-1206.

Ruff, Christopher B. 1995.   Biomechanics of the hip and birth in early Homo.  American Journal of Physical Anthropology 98:527-574.

Stringer, Christopher B., M. Chistopher Dean, and Robert D. Martin. 1990.    A comparative study of cranial and dental development within a recent British samples and among Neandertals.  In Primate life history and evolution, edited by C. Jean DeRousseau, pp. 115-152.  New York: Wiley-Liss.

Tillier, Anne-Marie. 1998.  Onotogenetic variation in Late Pleistocene Homo sapiens from the Near East.  In Neandertals and modern humans in western Asia, edited by Takeru Akazawa, Kenichi Aoki, and Ofer Bar-Yosef, pp. 381-389.  Plenum, New York.

Tillier, Anne-Marie.  1999.  Les enfants mousteriens de Qafzeh: Interpretation phylogenetique et paleoauxologique.  Cahiers de Paleoanthropologie.  Paris, CNRS Editions.

Trinkhaus, E.
1983. The Shanidar Neanderthals.  New York: Academic Press.
 

Trinkhaus, E. 1984    Neandertal pubic morpohology and gestation length.  Current Anthropology 25:509-514.

Trinkhaus, Erik, and Robert L. Tompkins. 1990.  The Neandertal life cycle: The possibility, probability, and perceptibility of contrasts with recent humans.  In Primate Life History and Evolution, edited by C. Jean DeRousseau, pp. 153-180.  New York: Wiley-Liss.

Young, Richard W. 1957.  Postnatal growth of the frontal and parietal bones in white males.  American Journal of Physical Anthropology 15:367-386.

Wolpoff, Milford H. 1999.    Paleoanthropology.  2nd edition.  Boston: McGraw-Hill.


    All views expressed in my blog posts are my own. The views of those that comment are their own. That's how it works.

    I reserve the right to take down comments that I deem to be defamatory or harassing. 

    Andy White

    Email me: [email protected]

    Enter your email address:

    Delivered by FeedBurner


    Picture

    Sick of the woo?  Want to help keep honest and open dialogue about pseudo-archaeology on the internet? Please consider contributing to Woo War Two.
    Picture

    Follow updates on posts related to giants on the Modern Mythology of Giants page on Facebook.

    Archives

    January 2024
    January 2023
    January 2022
    November 2021
    September 2021
    August 2021
    March 2021
    June 2020
    April 2020
    March 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    May 2019
    April 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    September 2014
    August 2014
    June 2014
    May 2014
    April 2014
    March 2014

    Categories

    All
    3D Models
    AAA
    Adena
    Afrocentrism
    Agent Based Modeling
    Agent-based Modeling
    Aircraft
    Alabama
    Aliens
    Ancient Artifact Preservation Society
    Androgynous Fish Gods
    ANTH 227
    ANTH 291
    ANTH 322
    Anthropology History
    Anunnaki
    Appalachia
    Archaeology
    Ardipithecus
    Art
    Atlantis
    Australia
    Australopithecines
    Aviation History
    Bigfoot
    Birds
    Boas
    Book Of Mormon
    Broad River Archaeological Field School
    Bronze Age
    Caribou
    Carolina Bays
    Ceramics
    China
    Clovis
    Complexity
    Copper Culture
    Cotton Mather
    COVID-19
    Creationism
    Croatia
    Crow
    Demography
    Denisovans
    Diffusionism
    DINAA
    Dinosaurs
    Dirt Dance Floor
    Double Rows Of Teeth
    Dragonflies
    Early Archaic
    Early Woodland
    Earthworks
    Eastern Woodlands
    Eastern Woodlands Household Archaeology Data Project
    Education
    Egypt
    Europe
    Evolution
    Ewhadp
    Fake Hercules Swords
    Fetal Head Molding
    Field School
    Film
    Florida
    Forbidden Archaeology
    Forbidden History
    Four Field Anthropology
    Four-field Anthropology
    France
    Genetics
    Genus Homo
    Geology
    Geometry
    Geophysics
    Georgia
    Giants
    Giants Of Olden Times
    Gigantism
    Gigantopithecus
    Graham Hancock
    Grand Valley State
    Great Lakes
    Hollow Earth
    Homo Erectus
    Hunter Gatherers
    Hunter-gatherers
    Illinois
    India
    Indiana
    Indonesia
    Iowa
    Iraq
    Israel
    Jim Vieira
    Jobs
    Kensington Rune Stone
    Kentucky
    Kirk Project
    Late Archaic
    Lemuria
    Lithic Raw Materials
    Lithics
    Lizard Man
    Lomekwi
    Lost Continents
    Mack
    Mammoths
    Mastodons
    Maya
    Megafauna
    Megaliths
    Mesolithic
    Michigan
    Middle Archaic
    Middle Pleistocene
    Middle Woodland
    Midwest
    Minnesota
    Mississippi
    Mississippian
    Missouri
    Modeling
    Morphometric
    Mound Builder Myth
    Mu
    Music
    Nazis
    Neandertals
    Near East
    Nephilim
    Nevada
    New Mexico
    Newspapers
    New York
    North Carolina
    Oahspe
    Oak Island
    Obstetrics
    Ohio
    Ohio Valley
    Oldowan
    Olmec
    Open Data
    Paleoindian
    Paleolithic
    Pilumgate
    Pleistocene
    Pliocene
    Pre Clovis
    Pre-Clovis
    Prehistoric Families
    Pseudo Science
    Pseudo-science
    Radiocarbon
    Reality Check
    Rome
    Russia
    SAA
    Sardinia
    SCIAA
    Science
    Scientific Racism
    Sculpture
    SEAC
    Search For The Lost Giants
    Sexual Dimorphism
    Sitchin
    Social Complexity
    Social Networks
    Solutrean Hypothesis
    South Africa
    South America
    South Carolina
    Southeast
    Stone Holes
    Subsistence
    Swordgate
    Teaching
    Technology
    Teeth
    Television
    Tennessee
    Texas
    Topper
    Travel
    Travel Diaries
    Vaccines
    Washington
    Whatzit
    White Supremacists
    Wisconsin
    Woo War Two
    World War I
    World War II
    Writing
    Younger Dryas

    RSS Feed

    Picture
Proudly powered by Weebly