Adult Proportionality in Small-Bodied Foragers: A Test of Eco-geographic Expectations

This study by Kurki et al. addresses the variations in body proportions of Later Stone Age (LSA) hunter-gatherers along geographic gradients and ecozones by comparing skeletal samples from different geographic areas and testing 3 hypotheses regarding the expected body proportions of LSA hunter-gatherers. The results are expected to follow Bergmann (1847) and Allen’s (1878) “rules”. Bergmann’s rule proposes that body mass increases in populations inhabiting cold climates. An increase in cellular activity results from the increased body mass therefore producing more heat. Allen’s rule proposes a similar thermoregulatory concept concerning a positive correlation between surface area, determined by limb proportions, and heat dissipation. Studies among human populations during the 20th century have demonstrated that Bergmann and Allen’s rules are applicable to human beings. Kurki et al. use eco-geographic studies to explain the relationship between 3 variables: (1) Latitude; (2) Environment; and (3) Human biological adaptations.

Samples
Sample 1. Khoe-San
Although sub-Saharan African groups are classified as being warm-adapted, low latitude populations, archaeological evidence suggests that the eco-geographic area inhabited by Khoe-Sans (descendants of the LSA hunter-gatherers who occupied the area) is significantly different. While the South African Cape is well below the North and South latitude division, the coastal climate is Mediterranean-like rather than tropical. The sample of 124 LSA hunter-gatherer skeletons (59 male and 65 female) from the Southern, Western, and Eastern Cape regions are dated between 240 and 7, 853 years BP.

Sample 2. Andaman Islanders
From the tropical monsoon climate of the Andaman Island, 31 proto-historic Andaman Island forager skeletons (16 male and 15 female) were collected. These skeletons date to around the mid 1800s and originated from the Greater Andaman Island which is situated between latitude 11° and 14° north.

Sample 3.
Kurki et al. use published literature to collect data representing skeleton samples from Northern and Southern Europe, North Africa, and Eastern and Western Sub-Saharan Africa.

Kurki et al. tested 3 hypotheses to explain the relationship between latitude, climate, and biological adaptations: (1) if the body proportions observed among LSA hunter-gatherers reflect those of populations inhabiting low latitude and warm climate regions (e.g. high limb to skeleton trunk ratio), LSA hunter-gatherers of the South African Cape inhabited similar environments; (2) if the body proportions of the LSA hunter-gatherers are similar to those of the European and North African samples, the LSA hunter-gatherers likely inhabited a Mediterranean-like climate; and (3) if the body proportions resemble those of the Andaman foragers and African Pygmies, LSA hunter-gatherers were adapted to warm climates. Although Andaman foragers and African Pygmies are relatively small-bodied populations, their bi-iliac breadth to stature rations are equal to those of non small-bodied warm climate inhabiting populations.

Materials and Methods
Kurki et al. calculated the brachial, crural, femoral, humeral, radial, and tibial indices and body breadth and mass to stature using the ratios in table 1.

Need to make space or else my post

Results
Limp Proportions:
Compared to the indices calculated for the 3 skeleton samples, the majority of the limb proportions of the LSA hunter-gatherers fall in between those of the North African and European samples.

Body Shape:
Proxy skeletal indicators were used to calculate stature ratios and the bi-iliac breadth determined the absolute body breadth. Kurki et al. found that body breadth decreased in relation to latitude, although the female African Pygmies have the largest bi-iliac breadth among the low latitude samples. Body mass also follows this trend, decreasing at lower latitudes. However, the Andaman Islander sample in which statures are similar to those of the African Pygmies have much more narrow bi-iliac breadths then expected. Sexual dimorphism was also observed in the LSA hunter-gatherer sample, although it was females who were generally larger then the males.

The results obtained in the study correspond to Kurki et al.’s third hypothesis. The skeletal morphology of the LSA hunter-gatherer sample falls between those of the European and North African Samples. Therefore, it appears that the Mediterranean-like climate of the southern African Cape had a greater influence on the LSA hunter-gatherer skeletal morphology than did the low latitude of the region. When compared to other African Sub-Saharan skeleton samples, the LSA hunter-gatherers and their descendants, the Khoe-San, have distinctly smaller limb proportions. From their findings, Kurki et al. caution against grouping populations into climate categories based on latitude. The eco-geographic patterning predictions on which Kurki et al. based this research was contradicted by the inconsistent body proportions of LSA hunter-gatherers and Khoe-San from the southern African Cape and the Andaman foragers.

Kurki et al.’s study of eco-geographic theories emphasizes that researchers consider the climate of regions inhabited by prehistoric populations. This is especially important when considering South African populations because the majority of archaeological sites are located on the coast. As demonstrated by Kurki et al., climates vary among and within latitudinal gradients. As a consequence, environmental adaptations may have developed for different climates then those predicted by latitude. However, the conclusions drawn from the study by Kurki et al. are based on methods that admittedly produce inaccurate results such as: “[…] the relationship between body mass and femoral height is not isometric, and the effect would be amplified in small bodied populations, such as those in this study” (p.30); There were several skeletons that were missing vertebral elements necessary to calculate skeleton trunk height. The height of these vertebral elements was estimated through a regression formula generated from a mixed-population reference sample which is rather problematic since the study sought to differentiate body proportions between populations; and only summary statistics were available for the skeleton samples obtained through published literature. Therefore, the samples were not directly comparable and a t-test identified differences in mean index value. The comparison of body proportions may have been somewhat altered. Finally, the indices and proxies for body proportions among different climates may be influenced by additional elements (e.g. life history parameters). Kurki et al. largely ignore the implications these additional elements may have on the body proportions of the sample populations in question.

Reference:
Kurki, H. K., J. K. Ginter, J. T. Stock, and S. Pfeiffer
2008 Adult Proportionality in Small-Bodied Foragers: A Test of Ecogeographic Expectations. American Journal of Physical Anthropology 136:28-38.

The Shape of the Neandertal Femur is Primarily the Consequence of a Hyperpolar Body Form

The Neandertal femur, when compared to anatomically modern humans, has distinctively larger articulations relative to absolute femoral length, a thicker rounded shaft, and a more obtuse angle between the femoral shaft and neck. In the early 20th century, when Marcellin Boule first described the Neandertal skeleton in detail, these distinct features of the Neandertal femur where attributed to a simpler social and cultural complexity which resulted in a high activity lifestyle. The author, Timothy D. Weaver (2003), notes that the assumption that elevated activity levels where consequences of Neandertal culture and social organization is unfounded because it is difficult to distinguish Modern Human from Neandertal cultures in the archaeological record. Although humans have the ability to buffer some environmental stresses through cultural adaptations, researchers now theorize that climactic adaptations account for the different dimensions of the Neandertal femur.

The theories now generally accepted by most researchers to explain different body dimensions within the same species were originally proposed by Bergmann and Allen. In summary, their theories state that “Endothermic species exhibit climate-related geographical patterns in overall size and body proportions” (p. 6926). Therefore, it is expected that humans inhabiting cold climates maximize heat retention though a lower surface area to body mass ratio, and humans inhabiting warm climates maximize heat loss through a higher surface area to body mass ratio. Cold-adapted humans generally have a small limb to trunk ratio, wider bodies, and reduced distal limb lengths. The “hyper-polar” or “hyper-arctic” body dimensions of cold-adapted Neandertals inhabiting glacial regions during the Pleistocene are most obvious in the absolute bi-iliac breadth and femur length relative to bi-iliac breath.

To determine if there is a relationship between femoral dimensions and climate induced body proportions, Weaver compares modern human males from different climates to fossils of Neandertal and near-modern humans (see tables 1 and 2 for sample summary). Weaver uses geometric morphometric methods to measure the overall hip dimensions of the 97 modern human males. These dimensions were calculated using 26 unilateral landmarks on the pelvis and 13 on the femur. The hip dimensions of Neandertal 1 and Skhul IV (near-modern human) were calculating using 13 unilateral landmarks on the femur. Because of fhe missing superior greater trochanter on the right femur of Spy 2, only 11 unilateral landmarks were available. Weaver’s results demonstrate that femur dimensions are correlated to climate induced body proportions. He found that:

“[i]ndividuals from cold climates tend to have relatively wide bodies as compared with individuals from warm climates… Cold adapted individuals have femora with large femoral heads and distal ends relative to length, thick and round shafts, and low neck; shaft angles; warm adapted individuals show the reverse pattern. These femoral changes are accompanied by pelvic changes. Individuals from cold climates tend to have wider pelvic apendatures, longer pubic bones, more flared iliac blades, more laterally pointing anterior-superior iliac spines, more anteriorly located iliac
tubercles, and more posteriorly rotated dorsal iliac blades relative to individuals from warm climates” (p.6927-6928).

Unfortunately, none of this is new information. There are also a few problems in Weaver’s testing methods which he does not address and have probably altered the results of his comparison. The most significant problem concerns Weaver’s disproportionate sample sizes. Weaver’s fossil sample, 1.75 (due to fragmentation) Neandertal femurs, and 1 near-modern human femur can not accurately represent populations. Although he uses only male femurs and pelvises in his modern-human skeletal sample, Weaver does not control for gender among his fossil samples, or age among any of the samples. Weaver’s calculations are also somewhat problematic as he uses 39 unilateral landmarks on the femur and pelvis of modern humans; however, he makes these same calculations from the fossil samples using only 13 (11 for the fragmented femur) unilateral landmarks only from femurs (not controlled for side, table 2). It appears that the only real value in Weaver’s test is in his comparison of femur and pelvic dimensions among modern humans inhabiting different climates. The sample of fossil Neandertal femurs used in Weaver’s study is too small to prove that the dimensions of the Neandertal femur are the consequence of a hyper-polar body form.

Reference:
Weaver, Timothy D.
2003 The shape of the Neanderthal femur is primarily the consequence of a hyperpolar body form. The National Academy of Sciences 100(12):6926-6929.

Sexual Division of Labor: To Cooperate or not to Cooperate?

Rebecca Bird’s “Cooperation and Conflict: The Behavioral Ecology of the Sexual Division of Labor” examines gendered differences in human subsistence behavior and attempts to provide ecological explanations for this division of labor that might be applied to human evolution and early hominid development. By exploring themes of cooperation and conflict in child-care provisioning, child-care constraints, reproductive goals, altruism and signaling, Bird concludes that cooperation alone does not maintain sexual division of labor but rather the conflict hypothesis is likely to maintain sex differences in subsistence.

The cooperation model suggests that by specializing in different resource acquisition, males and females are likely to maximize energy intake. David Lack suggested that a cooperative provisioning would ensure a higher reproductive success rate for both males and females. This is particularly true if resources are hard to locate. Lack’s hypothesis was based on the observation that nearly 90% of bird species participate in monogamous mating to insure stability in partnership (when insects were the primary diet base). In areas where resources are more easily located, an individual is likely to be self-sufficient and cooperation might collapse (67). It was eventually found that cooperation among the sexes for paternal care did not actually represent equal investment nor equal benefits. For example, male reproductive success is hindered by monogamy in that males have a higher variability than females. That is, males could acquire more fitness-related benefits by mating with more females. It is likely that a type of fathering that is less conflictual with reproductive fitness but less beneficial to offspring is engaged in. Bird argues that although female mate competition is rarely advantageous, if males control access to resources needed by females to reproduce (other than a new sexy pair of gametes), females might attempt to reproduce with many males in attempt to secure needed resources and might attempt to prevent their mates from mating with other females (67).

Bird argues that if sexual division of labor (SDL) results in specialization that would increase provisioning efficiency, three testable hypotheses emerge: 1) gender specialization would increase food going into the household in comparison to non-specialized cases, 2) male resource sharing should favor their own households, 3) men should have high payoffs for fathering in specialized cases.

Birds testable hypotheses are arguably geared towards the effects of specialization on males and male behavior rather than female behavior. What are some of the expected changes/differences in female behavior? Furthermore additional testable hypotheses include: higher success rates in subsistence acquisition (for example, in comparison to non-gendered specialized cases, or specialized males would have less success rates or greater energy cost-less efficient- in acquiring female-specialized resources and vice versa), greater variety in diet breadth and specialized tools.

Bird suggests that contrary to the notion that SDL would result in more reliable provision of food, Hiwi women have been found to contribute far greater than men. It has been shown that by participating in hunting, men loose out on the high returns that might be attained by aiding women in plant collection. Bird’s suggestion that Hiwi women contribute more than men goes against Gurven and Hill who claim that hunting is more productive than foraging where in the late wet season women who were pregnant and/or nursing collected 1,300cal/h, women not pregnant or nursing collected 1,600 cal/h and men collected 2,300 cal/h by hunting (although the reliability is not mentioned) (Gurven and Hill 53). Furthermore, Bird seems to equate caloric revenue as “contribution”. It should be noted however that women’s “caloric revenue” is mainly in the form of carbohydrates versus men’s “caloric revenue” include protein and lipids- both essential to human survival and functioning. Therefore, although women do not seem to gain calorie-wise in a specialized organization, they do in terms of the variety and essential nutrients provided by male contribution. Bird maintains however that even this need for a diversified diet does not explain why “sex differences exist… nor why it necessarily is men who obtain protein” (Bird 68).

Bird suggests that package size of acquired food plays a role in what and to whom food is shared with. She argued that “if big package hunting is primarily about fathering and provisioning, hunter-fathers must keep at least as much meat for their own households as they might if they had chosen small package hunting” (Bird 68). This does not seem to be the case with the Ache nor the Hazda. From this, Bird argues that costly hunting is engaged not because it provides for the family better but because it might “signal his quality as a mate or competitor” (71). The lack of evidence suggesting that providing meat gives male access to more sex leads Bird to suggest that the benefits of being a good under are indirect: the children of better hunters are less susceptible to mistreatment and infanticide and they are married to harder working women (71).

This however has been refuted by a recent study which suggests that hunters can and do influence or control distribution of meat. Kin, neighbors and cooperative partners are likely to receive a larger share of the kill as well as the nuclear family of the hunter. The hunter’s family has been shown to receive an average of 29.9kg/kill versus 13.5kg/kill which is distributed to other families (Gurven and Hill 54).

Furthermore, Bird states that “by hunting [males] can broadcast that skill to the large audience that is attracted to the kill. The fact that big game is shared is incidental” (72). This however brings into question the dynamics involved in large kills which are made successful by cooperation. To what extent do the men participate and how is individual skill recognized? How is more skill accorded to one hunter over the other and how does this get transferred from the kill site to the campsite? One would expect mechanisms that limit individual recognition or prestige to be in place when hunting is conducted in a group setting. How does this get altered when hierarchies (example chiefs participating in the hunt) are in place? It seems that signaling can only function if the group of males hunting allows for recognition of outstanding individuals, or if the group is composed of several hunting parties for attribution to a single individual is more likely in hunting of smaller game (which goes against the notion that hunting is costly behavior because of a lack of distribution control and physical danger).

Bird concludes that SDL will be stronger where males benefit more from investing in mating opportunities over provisioning ones.

Despite some data conflict with later published works, this paper is a good summary of the existing theories of SDL and gender specialization. It does however focus very heavily on an andocentric perspective of specialized subsistence costs and gains to the point where females are depicted as being acted upon, and simply having no choice in the matter. Females seem to have no choice but “cope” with the male’s preferred mating choices (to provide or not to provide?).

Also, it would have been insightful to provide additional ethnographic information that was not based solely on the Hazda or Hiwi.


Works Cited

Bird, Rebecca
1996 Cooperation and Conflict: The Behavioral Ecology of the Sexual Division of Labor. Evolutionary Anthropology: Issues, News and Reviews 8(2): 65-75.

Gurven, Michael and Kim Hill
2009 Why do Men Hunt? A Reevaluation of “Man The Hunter” and the Sexual Division of Labor. Current Anthropology 50(1): 51-74.

Human Social Evolution

Robert A. Foley’s “An Evolutionary and Chronological Framework for Human Social Behavior” examines the chronological framework and ecological basis for human social evolution. Foley argues that the combination of male kin-bonding and selection for energetically expensive offspring played a key role hominid social evolution and that this evolutionary path was not unitary or the consequence of a single event.

Foley maintains that although primatology, anthropology, and paleobiology have contributed behavioral and ecological theories to human social evolution, it is likely that “specific interactions between populations and their environment occurring cumulatively over millions of years”, rather than an inevitable evolutionary track, resulted in today’s observed human social behavior (96). Suggesting that the “particular times and … particular places [are] paramount”, Foley focuses on a chronological retelling of human social evolution. He suggests that human ‘sociality’ is a characteristic of anthropoid primates dating as far back as 35 mya and not a trait exclusive to humans (97). This is based on the argument that hormonal and biochemical mechanisms mediating behavior is similar across anthropoids.

The emergence of monogamy or instances of monogamy among anthropoids is associated with the inability for females to simultaneously have access to a resource base and a (undefined) “component of male contribution to infant survival” (99). According to Foley, monogamy is fairly unstable as if males are able to acquire more mates they will likely attempt to do so. Some primate groups have been shown to have various social states and are flexible within them. It is argues that this may have been the origin of social states which would have diverged with niche separation (99). In the development of hominids, however, an increase in infant dependency is likely to have affected the frequency of monogamy. Foley notes that an increase in infant dependency (as observed in chimpanzees) is typically dealt with by increased female kin-bonding which provides “allomothers”, lowering energetic costs for mothers. The lack of female kin-bonds in early hominid groups would have increased the importance of male-female bonds and food sharing.


This is supported by a distinct divergence between cercopithecoids and hominoids where the former show significant female kin-bonding and the later were likely characterized by “small social units made up of one male, one or more females, and young. It is suggested that the early diversification of Hominoidea between 25 to 20 mya was likely to have established the “small core units of homoid social life” of which gorillas, orangutangs and Gibbons are examples (100).

With the retreat of forests and the expansion of savannah grasslands, Foley argues that an increase in day range length, home range area and time for foraging was likely to have occurred due to the overall patchy dispersal of resources and increased seasonality. This is seen as a factor likely increasing the formation of small(er) social units and a strengthening of family bonds. (101-2). Although there have been disputes as to whether this was the ancestral condition (and that common chimpanzees departed from this model). The author proposes that it was likely an independent adaptation of the hominid lineage to open grasslands (102).

The increase in seasonality on the savannah is interpreted by Foley to have triggered an increased reliance on meat around 2 mya. This new reliance would further shift social relations and social structures such that this new behavior is different from australopithecine populations (102). The reason for this differentiation is not explained. This shift in diet is argued to have triggered an increase in encephalization , which consequentially would further alter human social behavior. Foley argues that for encephalization, being extremely costly, to occur and continue to develop there had to be positive selective pressures. The selective pressures for increased encephalization are argued to be “Greater meat-eating [as it] provided more energy, allowed for reduced energy expenditure, and acted as a selective pressure leading to greater levels of sociality” (102). This statement however relies on the assumption that during ecological changes gathering became insufficient and no longer provided the necessary calories and that hominids were skillful enough to hunt, kill, and butcher meat without expending more energy than attained (thus reducing energy expenditure). Also this suggests that encounter/success rates with prey were high enough to encourage increased meat consumption.

Foley further suggests that:

…during the period of 2.0 to 1.0 Mry the expected shift in social organization might well have been towards more intense and extensive male alliances…provided a premium in terms of foraging behavior under these new ecological conditions. Females associated with male groups that were numerically larger and effective at acquiring, and probably protecting resources (Foley 104).

This statement assumes that by 2-1 mya, males were the ones doing the hunting and that it was this male behavior that led to an increase in socially complex behavior. The notion that females would start to associate themselves with large male groups runs contrary to the small hominoid family unit previously argued by Foley. Also, this assumes that females were ineffective “at acquiring and probably protecting resources” and therefore had to rely on males (104). Changes in female behavior and therefore contribute to social complexity are ignored or are only discussed in relation or in response to male shifts in behavior.

Foley suggests that group size increased by 300,000 years BP to the point where grooming was no longer efficient for the maintenance of social relationships and therefore language emerged. The increase in brain size to 1000 grams during this time would have also prompted increased male competition and conflict between mating strategies as maturation of infants would have slowed and longer inter-birth periods would become characteristic (104-5).

The first 80,000 years of AMH is argued to not be characterized by social behavioral innovation but rather differences start to emerge around 40,000 BP and are not the founded in specific behavior but rather the propensity for dispersal which is argued to have come about as a result of increased hostility between males in male bonded kin-groups (106). As size increases, competition also increases and resulted in “demographic fission of communities” which would be composed of mainly kin-based groups (107). This is an interesting suggestion and would be consistent with fission of modern hunter-gatherers but the groups would have to maintain adequate genetic variability within the group or have a certain amount of inter-group exchange. The explanation of fission due to male hostility however seems incomplete and Foley ignores resource competition among other possible female conflicts (though it is not made clear if male hostility includes this).

Foley also claims that at about 30 kya, long-term evolutionary changes in behavior come to halt and are only reinstated with the beginnings of agriculture which require a “shift from small mobile hunter-gatherer groups to larger and more sedentary farming communities” and would have resulted in different social interactions and therefore a change in basic social structures (108).

The author maintains that the nature of social evolution must be considered similar to any other evolutionary process as one that is additive and that what we observe today is the product of individual elements. He argues that the “relationships between members of the same sex have remained more stable than relationship between the different sexes”. This is significant in that the author moves away from any type of biological determinism and suggests that male-female relations are flexible (and therefore existent unequal gender relations are not naturalized).

Finally, the author ends in summarizing the proposed “human revolution” theories of the Upper Paleolithic. These include language and symbolic thought. He stresses that “there is no clear anatomical boundary between archaic and modern” and “there is continual and regionally variable evolution in human cranial from 100-10kya” (113). Behavioral changes only become clear around 45 kya and this is restricted to Europe and the Mediterranean. This leads the author to suggest that symbolic expression was a regional phenomenon and not a reflection in change of “human global traits”. He claims that genetic diversification was not specific to the Upper Paleolithic but was present in both the Pleistocene and Holocene.

This paper presents a series of hypothesis for social evolution among early hominids and appropriately suggests that social evolution was not the result of a single event or drastic change. It is interesting that Foley suggests a regionally diverse hypothesis over a structural one. This paper was well argued though may have been more convincing if archaeological evidence was provided.

Works Cited

Foley, Robert A.
1996 An Evolutioanry and Chronological Framework for Human Social Behavior. In Evolution of Social Behavior Patterns in Primates and Man: A Joint Discussion Meeting of The Royal Society and The British Academy. W. Grunciman with John Maynard Smith and R.I.M. Dunbar, eds. Oxford: Oxford University Press.

Absolutely no TV until you’ve sharpened your biface...

Technological Efficiency and tool curation

Bamforth has acknowledged that tool curation is often defined in relation to its efficiency, but amid the multiple components involved in the activity, what is efficient is rarely specified. As stated in his 1986 publication, Technological Efficiency and Tool Curation, Bamforth seeks to clarify the notion of curation, assess several previous attempts explaining why curation occurs, and to present a hypothesis accounting for several important aspects of curation behavior.
Binford (1973, 1977, 1979) outlined two contrasting aspects of technological organization. According to him, curated tools are effective implements for a variety of tasks in which their structure has been designed with a particular function in mind. These pieces are maintained through numerous tasks, transported, and recycled when exhausted. To the contrary, lithic technologies based on expediency comprise manufactured tools, which are then used and discarded upon task completion. Therefore, curation should produce technologically sophisticated tools with formal distinctions designed to facilitate particular tasks, whereas expedient tools produce technologically simple assemblages portraying less patterned pieces.
Attempts to explain the occurrence of curation in the archaeological record, by both Binford (1973, 1977, 1979) and Torrance (1983), have lacked the specificity necessary to address the full behavioral complexity intrinsic to the process of curation. Binford links curation to subsistence-settlement organization, while Torrence attributes curation to the problem of scheduling different activities co-occurring in time.
Bamforth critiques these two stances with two simple explanations. He first criticizes both Binford’s and Torrence’s inability to address the full suite of behavior intrinsic to curation. Torrence’s definition’s failure to predict curation processes occurring after the initial design is its downfall, whereas Binford’s definition of curation encompasses an additional four aspects of stone tool manufacture. However, Bamforth recognizes that all five kinds of behavior need not occur in concert all the time. His example, that the flaked knives used as butchering tools in communal Plains bison kills were apparently manufactured in advance, resharpened, but then discarded, without being recycled, transported, or applied to other tasks beyond their primary function, indicates that different aspects of “curation” are circumstance dependent and that “no single measure of technological ‘efficiency’ can be universally applied to explain them” (P.39).
Ultimately, technology is structured by the requirements of an activity or set of activities that constrain variation in all aspects of tool manufacture and use (P.39). Technological efficiency appeases these requirements with minimum energy expenditure. Alternatives to extensive curation (i.e.: resharpening a dulled edge vs. discard and creating a new tool) are efficient only in the absence of sufficient raw material. Maintenance and recycling are thus closely related to raw material availability and not directly, as proposed by Binford, to settlement organization or the time limits, as advocated by Torrence, on the activities for which tools are used.
If processes of maintenance and recycling are a function of raw material availability, than a second major criticism is unveiled. Both definitions ignore local patterns of lithic resource availability, which inevitably places fundamental constraints on technology and subsequent curation processes. In light of this, Bamforth states, “we must examine these aspects of lithic resources in conjunction with the ways in which humans are or were organized to satisfy their other needs” (P.40).
Bamforth illustrates this response to material shortage using an example from the American Southern Planes. The Lubbock Lake site has hosted intermittent occupations over the past 12,000 years including significant Folsom, Plainview, and Firstview portions of the Paleoindian period.
The lithic assemblage is composed of three basic types of raw material, ranging from vey high-quality chert, to very low-quality silicified caliche. Bamforth’s hypothesis stipulates that maintenance and recycling rates should vary with access to raw material. Assuming distance to a source effects access, this range of materials should demonstrate varying rates of retouch (curation) depending on the distance between the source and the site. Therefore, tools manufactured from material originating in more distant sources should be subject to more frequent retouch in an effort to prolong its use-life.
In accordance with this hypothesis, tools manufactured from distant sources were subject to a high frequency of curation. In addition, based on their material, tools differed in their designated tasks. Durable but granular quartzites and cherts were predominately selected for wood work, while non-local stone, as expected, was used frequently for all tasks. In short, tools constructed from non-local materials were subject to higher maintenance and recycle rates reflecting their multipurpose nature. Bamforth acknowledges that the Lubbock Lake assemblage depicts a toolkit organization based on the different distributions and natures of the various sources of stone used to manufacture it (P.48).
The Lubbock Lake example affirms Bamforth’s original statement; that tool curation is a complex set of behaviors that cannot be explained by any single factor.

Bamforth, Douglas B.
1986 Technological Efficiency and Tool Curation. American Antiquity 51(1): 38-50.

Accumulation of Stochastic Copying Errors, Akumulation ov Stokastic Coppying Errrors, Akoomulajon ov Stokasic Coppyng Errrers

The Accumulation of Stochastic Copying Errors Causes Drift in Culturally Transmitted Technologies: Quantifying Clovis Evolutionary Dynamics. Hamilton and Buchanan, 2009.
This paper looks at the application of Eerkens and Lipo’s (2005) model on determining causes of copying errors that result in variation in material culture, and how different forms of cultural transmission or social learning affect the amount of variation. Eerkens and Lipo’s model basically seeks to predict the amount of variation given different factors and circumstances. Unlike Eerken’s and Lipo (2005) however, the Hamilton and Buchanan seek to determine not only frequency of variation but also its distribution through measuring the mean, variance, skewness and kurtosis.
Hamilton and Buchanan adapt Eerkens and Lipo’s model to analyze the variation found within Clovis point sizes, to determine if this variation is stochastic (random) or deterministic (result of biased selection). They also argue that this model can be used to track the movement of people across space and time, due to the drift effect of variation in Clovis point size.
Hamilton and Buchanan are particularly interested in drift “which is caused by population fluctuations and subsequent founder effects. A second source of drift is the accumulation of neutral, unbiased, but proportional copying errors through time.” (Hamilton and Buchanan 2009, page 55).
Hamilton and Buchanan term the first model the ACE, accumulated copying error model, which determines variation as a result of the accumulation of stochastic, imperceptible errors during transmission events. Thus the ACE is unbiased vertical transmission from a master to an apprentice. The Weber fraction explains that when humans try to make a copy of something without measuring it directly, their copy will vary by up to 5%. This difference becomes a source of variation which becomes compounded as copies of the copy (and so on) are produced with up to 5% copying errors at each generation.
From the ACE model, Hamilton and Buchanan develop the BACE model, which stands for biased accumulated copying error model. The BACE is similar to the ACE except cultural transmission in this case is biased.
Hamilton and Buchanan go on to create complex equations and simulations to test their models and the results of copying errors. First they test the ACE model, unbiased stochastic copying errors. Their simulation shows negative drift of the mean over time. Next, Hamilton and Buchanan test the BACE model, which is the biased accumulation of copying errors. They identify multiple sources of biased transmission. One of these is conformism where “each individual within a population chooses either to copy the most frequent variant, often given by the population mean […] a process akin to stabilizing cultural selection, […]or follow the rules of vertical transmission” (page 58). Another source of biased transmission is prestige bias, “where prestigious individuals influence social learning [because] each individual within a population chooses either to copy a prestigious individual […] or follow the rules of vertical transmission” (page 58). Here, prestigious individuals are skilled flintknappers from whom beginners would rather learn from. Like conformists, prestigious individuals and their followers are most likely to produce projectile points close to the mean variant. Both are analytically equivalent because the bias is towards the average variant, thus under biased accumulation of copying errors variation should be overall reduced. However copying errors still occur and result in negative drift of the mean. Thus it is predicted that projectile points should decrease over time at a slower rate than unbiased ACE.
The authors propose a case study on Clovis projectile points. The authors look at 232 points from 26 sites across North America. These sites are either caches, camps or kill sites. Also look at radiocarbon dates to determine time scale. This data shows their hypotheses to be true. They are as follows:
Hypothesis 1: frequency of distribution is lognormal as predicted by the ACE and BACE models.
Hypothesis 2: mean size of Clovis points decreases over time, as a function of distance from origin. Site type and raw material are non-significant factors.
Hypothesis 3: size of decrease in size caused by stochastic cultural transmission should be about 5%, as predicted by the Weber Fraction. Copying error accounts for about a quarter of the variation found in Clovis points.
Hypothesis 4: Variation should remain constant over time, suggesting variance is “bounded by transmission bias as predicted by the BACE model” (page 65). This highlights the relevance of biased cultural transmission is social learning.
Since the case study fits within the authors’ models and prediction, they argue it is strong support in favour of their hypotheses. Thus point sizes may be used as a tool for interpreting Clovis populations. They argue that the movement of people across North America can thus be found by analyzing average point size. Specifically the authors argue that by analyzing variations they can determine that Clovis populations were stable and spread rapidly while maintaining long distance social networks.
Furthermore, the authors conclude that the decrease in Clovis point size over time is a result of accumulated copying errors, and not a deterministic selection for smaller points. In other words, points got smaller because of errors in copying and not because smaller points were actually better for hunting due to ecological changes. That is not to say selection never occurred, but rather it simply wasn’t the main cause of the drift in mean size. Variance may have been reduced due to both conformist and prestige bias, due to the fact that the mean was probably the optimal form.
One interesting fact about this paper is that although the authors cite Eerkens and Lipo for the weber fraction figure, Eerkens and Weber say it is a 3% error while Hamilton and Buchanan say it is “up to 5%”, but never discuss where this difference comes from.
Despite this, the authors successfully applied Eerken and Lipo’s previous model, and expanded it. Use of these models in analyzing variation among artifacts can be very useful to archaeologists in interpreting hunter-gatherers behaviour. Use of these models can identify where variation is significant or not, and whether it is linked to particular types of cultural transmission. Furthermore, archaeologists may be able to interpret movement of populations over time. There are without a doubt other factors not accounted for by these models, including social relationships, skill level, etc etc, yet I think the models remain valid.
Clearly, research in evolutionary archaeology can result in new ways of interpreting data.


References:
Eerkens, JW; Lipo, CP. 2005. Cultural transmission, copying errors, and the generation of variation in material culture and the archaeological record. Journal of Anthropological Archaeology 24 316–334
Hamilton, MJ; Buchanan, B. 2009. The accumulation of stochastic copying errors causes drift in culturally transmitted technologies: Quantifying Clovis evolutionary dynamics. Journal of Anthropological Archaeology 28 55–69

Cultural Transmission, Copying Errors, and the Generation of Variation in Material Culture and the Archaeological Record. Eerkens and Lipo 2005.

In this paper, Eerkens and Lipo make a model to understand the means by which variation in material is produced. It is important to realize that here the authors are discussing variation among the same type of artifact, for example variability in thickness of the same type of ceramic pot or projectile point. They look specifically at copying errors as a source of variation, and how methods of cultural transmission either reduce, increase or maintain this variation. They have thus constructed simple models to quantify expected distribution of variation through time under different conditions. The authors claim their arguments can be extended to other aspects of human culture, although they never go into the meaning of this statement.

The authors discuss what produces variation. Although previous work has been done on the subject, it has focused on variation of types and not variation within types.

They begin by exploring cultural transmission, noting its difference with biological transmission, and thus the difficulties in tracking its complex processes.

According to the authors, variation can occur at different points in the creation of material culture in the archaeological record. There are: (1) transmission of instructions, (2) execution of instructions, (3) result of using different raw materials (Eerkens and Lipo 2005, page 319).
The authors propose a schematic for the generation of variation of material culture, which I have replicated here: (sorry about the bad reproduction, I had no choice but to up it up as an image)

The authors argue that the left and right column (stochastic and biased errors, respectively) create different kinds of variation patterns. Stochastic errors are compared to random mutations in genetic transmission, and therefore do not have a predetermined direction. This supposedly leads to smaller scale variation. On the other hand, biased errors, which are intentional, are greater and can be directional. This is because cognitive processes can “sort variation” (page 320). Thus when a hunter-gather wants to create a new form (ei: invent something new), it is not produced by random errors or from a blank slate, but with intentional modifications of a prior known (inherited) form that is believed to be an improvement.

However the authors are mostly concerned with the first column and variation as a result of stochastic copying error. They describe the Weber Fraction, a well known concept, which says due to the human threshold of perception; humans produce 3% error when copying something without being able to directly measure it. Thus we can expect a variation of 3% across a type of artifacts stemming from imperceptible human error. As the errors accumulate, they become perceptible over time, resulting in drift.

In their simulations, unbiased copying errors cause variation to be transmitted and increase over time, although the rate of increase slows down over time. They simulate biased transmission, notably conformist and prestige transmission. Conformist transmission means “individuals conform to the average value […] of the entire previous generation” (page 323). In conformist simulations, variance equilibrium is always eventually reached, although the time it takes to reach that equilibrium depends on the strength of conformity. Overall, this reduces the effect of drift. In prestigious bias, individuals are more likely to try to copy from prestigious flintknappers, which are assumed to produce variants closest to the mean. Thus, prestigious bias should reduce variance. However, prestigious individuals may not necessarily be producing traits that are closest to the means, and individuals may have to choose between multiple prestigious flintknappers, therefore drift is possible. Overall, biased transmission reduces variability caused by the accumulation of copying errors throughout time.

The authors then apply this model to two case studies. The first involves the basal width and thickness of Owens Valley projectile points. Since variation of basal width reduces over time, it suggests non-copying errors may be factors, in other words a biased transmission process may be operating. Thickness however, becomes increasingly variable throughout time, suggesting stochastic copying errors. The second case study involves Illinois Woodland Pot Sherds. Thickness remained constant over time, probably because thickness is important to the function of a vessel and thus non-functioning thicknesses would be weeded out. It would seem that a particular thickness was a trait that was selected for, thus drift was not caused by stochastic copying errors.

The authors admit in their conclusions that there are surely many other factors at play, including changes in settlement patterns, social organization, individual memory, concept of ideal form, etc. However copying error seems to be universal, and thus this paper provide us with a null hypothesis with which we can test data to determine the source of variance over time in the archaeological record.

I like that the authors created a null hypothesis. They build a model based on a universal human trait, and therefore can theoretically be used in any case study and is then very useful to archaeology.

I find it interesting that the trend of random error accumulating over time is the same as that in biological evolution with a rate of increase slowing down over time. The cause of this in biology is history; although here is always variation in traits of organisms, the extent of that variation depends on the organisms’ genetic history (Bell 2008). If this the same in cultural information, even though there are errors, a previous artifact from a long time ago is still remembered, even though it is not the one being copied? I think there are many implications of this that can be more thoroughly investigated.

Clearly, creating a theory of cultural evolution based on Darwinian evolution has many challenges, but as the authors have demonstrated, with more research in this area it is possible to build models appropriate for archaeology.

References:
Bell, Graham. (2008). Selection: The Mechanism of Evolution, 2nd edition. Oxford University Press.
Eerkens, JW; Lipo, CP. (2005). Cultural transmission, copying errors, and the generation of variation in material culture and the archaeological record. Journal of Anthropological Archaeology 24 316–334.