First through Fifth Week Notes From Lectures and Readings
Terms and Concepts with which to be familiar
- >mismatch theory
- the forms of evolution (stabilizing, diverging, and directional)
- adaptation and natural selection
- genotype and phenotype
- reproductive selfishness
- obligate and facultative traits
- units of selection: group and individual
Issues in Hominid Evolution
- The evolution of cranial capacity and the roles of diet and group size.
- The evolution of bipedal locomotion and thermal regulation in a hot climate.
- What do changes in sexual dimorphism have to say about mating systems and paternal investment in offspring?
Third Week Notes from Lectures and Readings
Chapters 1 and 2 in Kelly: some of the basic issues considered
- The notion of progress (control over nature and rational thought) in cultural evolution and the role of hunter-gatherer society.
- Hunter-gatherer society at the bottom of the social evolutionary scale because:
- few material possession
- limited private property
- moral limitations (improvident, lazy, and dumb)
- Initial search for archetypal hunter-gather society (Service, Radcliffe-Brown, and Steward) replaced by quest to understand the factors that underlie diversity.
- Hunter-gatherers as societies without domesticated cultigens and domesticated animals (save the dog): the fundamental definition.
Steward's Typology of bands: an attempt to understand diversity:
Man the Hunter Symposium, The Generalized Foraging Model or One Myth Replaces Another:
- low population density
- lack of territoriality
- minimum food storage
- flux in band composition
- Sahlins’ notion of affluence (little work, no worry about future, and want little and feel affluent).
Supplements to Kelly: historical views of hunter-gatherers
Early cultural evolutionary schemes regarded them as:
- immoral or amoral
According to Hobbes in The Leviathan:
"No culture of the earth; no navigation ... no account of time; no arts; no letters; no society; and which is worst of all , continual fear, and danger of violent death; and the life of man, solitary, poor, nasty, brutish and short" (1651).
According to Lubbock (1879) in his The origin of civilization and the primitive condition of man. Mental and social condition of savages:
"...he is a slave to his own wants, his own passions; imperfectly protected from the weather, he suffers from cold by night and the heat of the sun by day; ignorant of agriculture, living by the chase, and improvident in success, hunger always stares him in the fact, and often drives him to the dreadful alternative of cannibalism or death."
A more recent romantic ecological model painted an opposite picture. According to Flannery:
"We no longer think of pre ceramic plant collectors as a ragged and scruffy band of nomads; instead, they appear as practiced and ingenious team of lay botanists who know how to wring the most out of a superficially bleak environment."
Challenges to the Generalized Foraging Model
- Levels of work much higher than Sahlins or Lee claims (see table 1-1 in Kelly).
- Evidence of chronic to seasonal under-nutrition.
- Meat and men's labor shown to be more important by C. Ember.
- Egalitarianism either sexually or by age varied considerably between cultures.
- The problem of history: the notion of "professional primitives", powerful groups forcing foragers into marginal environments (the "Kalahari Debate"), the role of trade and capitalism in moving them into a world economic system, and economic ties to settled agriculturalists and pastoralists (see Bailey Chapter 2 for discussion of Efe Pygmy ties to Lese).
- Patrilocality more common than bilocality (C. Ember).
> Kelly shows that there has been a strong tendency to over generalize about the nature of hunting and gathering society, an attempt to search for or define prototypical forager society. In the works of Radclife Brown and Elman Service the patrilocal and territorial patrilineal band with a strong emphasis on hunting was argued to be somehow a fundamental characteristic of foraging society. In "Man the Hunter Symposium" Lee claimed that gathering and bilateral and fluid social groupings were the norm. Neither of these claims can stand up to comparative scrutiny; and even if they could they lead us away to identifying the factors that account for diversity in foraging life. Steward was one of the first to take on this approach in his attempts to link residential patterns with foraging emphasis. Explanation of diversity (instead of explaining diversity away) is now an essential goal of processual archaeologists (e.g., Binford's association of latitude and storage and foraging emphasis), evolutionary ecologists (e.g., research on diet breadth), and others who see variation as the key to theory development.
Fourth Week Notes from Lectures and Readings
Important concepts from Kelly's Chapter 2:
- culture area
- culture core and cultural ecology: permissive and restrictive environments
- ecosystemic approach: energy flow as a way to model foraging-environmental relations and homeostasis.
- behavioral ecology: methodological individualism, optimization
Points from Laughlin (Chapters 1-5)
- Aleut demography: longevity, male subsistence mortality, and near extermination by Russians
- Physical geography and ecology and how they determine resource richness
- Childhood training for hunting
- The process of hunting and major skills in hunting
Points from Bailey: Chapters 1-2
- A movement away from typological accounts to an emphasis on " seeking the predictors of variation among contemporary hunter-gatherers, [so] we may discover the prevalence of these predictors and their effects in the past. (p. 2).
- On theory and the facts of description: "We cannot go out and describe the world in any old way we please and the sit back and demand that an explanatory and predictive theory be built on that description (Lewontin, 1974:8)."
- See page 8 for the set of questions that inform Bailey's research.
- The role of ecological and social history on Efe life and their relations with settled agriculturalists.
Points from Bailey: Chapters 3-4
- Behavioral sampling methods: scan and continuous.
- Method chosen depends on question asked.
- Time Allocation Results:
- subsistence and maintenance 5.7 hr/day
- seasonal emphasis on honey gathering and trade
- minor role of fuel and water and cooking for men compared to women
- lack of correlation between marital status and maintenance and cooking
- low levels of child care
- no correlation between age or marital status and labor time
- smokers are poorer
- men prevented from working 21% of time owing to illness.
Points from Kelly: Chapter 4
Binford’s foragers and collectors based on residential and logistic mobility. Foragers move people to food while collectors have residences that are not based on food location (alone or all the time). The determinants are distribution (patchy or even) of resources and their seasonality.
Five dimensions of mobility
- number of residential moves per year
- average distance covered
- total distance moved
- total area used over a year
- average length of logistical foray
Primary biomass inversely related to effective abundance of vegetable food (tropics have much of biomass in inedible structural components) and inversely related to effective game density.
Residential Moves per year
Positive correlation (r=0.86) between number of residential moves per year in 16 normal tropical foragers. The ones deleted either depend on fishing (Andamanese) or those linked to horticultural villages (Mbuti), and, apparently, some desert groups (Hadza, Kung) who may be tethered by water considerations.
Average distance per residential move
Negative correlation between effective temperature and average distance of residential move. Three types of groups are exceptions to this rule:
1. Arctic groups who have no access to large migratory herds (caribou) as a result they must, like tropical, forage on solitary animals (therefore move more than one would predict).
2. Plains bison hunters with horses move less than predicted because they quickly hunt out area. Variety of factors here but probably the added mobility of horses as a search vehicle allowed them to leave earlier because of easy mobility.
3. Northern fishers move very short distance because they are constrained by the territory of others.
Logistical mobility and territorial coverage
Given that the food resources of carnivores are more dispersed, one would expect a positive correlation between territory size and degree of dependence on hunting. Indeed, there is a positive relationship between dependence of meat in diet and territory size (r=0.66) and the relationship is curvilinear in that it increases very rapidly and then less rapidly.
Suggests that gatherers should cover territory more thoroughly through residential mobility. Thoroughness of coverage is dividing total distance moved residentially each year by area exploited each year.
Individual Foraging and Group Mobility
Essentially, people eat their way out of places and then move.
Figure 4.9 shows daily return rate from foraging is negatively associated with distance to foraging area. Foragers who must gain a lot because of large families have a shorter distance from which he or she can travel. He concludes that the effective foraging radius “.. is largely a product of the return rates of the available resources and the degree of dependence on them (or how much one must supply of family’s daily needs).” “As average resource-return rates decline (as would happen if lower-ranked resources are added to the diet) and/or as the amount of food a forager must bring back increases, the effective foraging radius becomes shorter and the family will probabl ymove more frequently and for shorter distances.” (p. 135). This means that only high return rate foods can be taken at a distance [this is a example of diet breadth contraction and expansion that Hames and Vickers show].
Figure 4.10 shows that central placed foragers attempt to minimize travel time. However, as the costs of movement increases (e.g., the distance to a new location is great or travel is difficult as in his comparison of moving through a level prairie versus a muskeg swamp) then foragers will stay in the same place for longer. Also, housing should be tailored to mobility needs such that frequent movers should have low cost housing while infrequent movers should have (or can have) high cost housing.
Interesting conflict of interest arises between large and small families: large families may wish to move less frequently than small families because the costs of movement for large families is greater probably as a consequence of having to haul children. Thus, this situation of being on different movement schedules may create disagreements about the timing of movement that may lead to band fissioning.
If return rates over the entire environmental range are low then foragers should be expected to remain in same place for a longer period of time since the difference between staying and going is small. Therefore, we expect a positive correlation between environmental richness and mobility. (See figure 4.14 demonstrating this with marginal value theorem.) The relationship between primary productivity and frequency of movement is probably a consequ4nce of decreased return rates and not because of better opportunities elsewhere (much higher return rates elsewhere rather than depleted local stocks).
Consequences of sedentism include:
- social hierarchies
- hereditary leadership
- unequal access to resource
- gender inequality (: he is wrong here)
Sedentism is a continuum. It appears that as residential mobility decreases logistical mobility increases. Idea that groups become sedentary because of resource abundance (called “Garden of Eden Hypothesis” by Binford) is called into question when he suggested (with no proof) that mobility was maintained in order to gain information about resources in the environment that they might have to fall back on (or the “Grass is always Greener on the Other Side of the Valley” hypothesis).
He concludes (after dealing with depletion, movement and set up costs) that sedentism could occur in the context of local abundance and regional scarcity. Brings in a domino theory: one group becomes sedentized which restricts resource access of neighbors (assuming initial overlapping becomes territorial), which then causes them to become sedentary.
Kelly wisely says:
- “We cannot claim that hunter-gatherers are mobile because they value mobility, however, for this only raises the question of why they value mobility.” (p. 153).
Hadza Women’s Time Allocation, offspring provisioning, …”
Current Anthropology 38: 551-577 (1997)
J. F. O’Connell
N. G. Blurton Jones
This paper deals with an important issue in human evolution from a theoretically sophisticated perspective that is supported by solid empirical data obtained through an excellent research design. Menopause is an evolutionary puzzle because nearly all female organisms reproduce until they die. For human females, reproduction ceases around age 45 but death does not occur until the age of 65 to 75. Previous research by Hill and Hurtado (discussed towards the end of the article) indicates that investment in offspring following menopause does not compensate for the loss of reproduction. What this means is that the fitness consequences of investing in offspring or grandoffspring are not sufficiently high to offset the cessation of reproduction. In short, it would be better to reproduce between the years of say 45 to 70 than to invest in children and kin.
Contrary to most:
- The authors change the question from the evolution of menopause to the evolution of long life spans. This is important since we live longer than we should for a primate of our size and therefore we need to explain the adaptiveness of this evolutionary trend (Life history theory suggests that for large bodied apes, maximum life span is 50 years.) As a consequence, the evolution of menopause must be understood in this context.
- It is important to realize that human reproductive life spans are no shorter than other hominoids (the onset of menarche and menopause in chimps and humans is about the same). Therefore, the issue is an increase in life span and menopause becomes a mere side-effect and not an adaptation
- Furthermore, they expand fitness enhancing effects from grandmothers on grandchildren to include fitness enhancement on the fertility and survivorship of collaterals such as nieces and also wives of male offspring and collaterals. This shift and expansion represents a fundamental restructuring of the problem that may ultimately lead to its resolution.
- A key element in their model is the recognition that human foragers frequently target resources that cannot be efficiently or effectively taken by sub-adults. This is in stark contrast to chimps where after weaning a young chimp is on its own in terms of gaining sufficient food to survive and mature. They assume that these resource are of sufficiently high quality or exist in sufficiently high density to overcome the cost of having to provision with these difficult to acquire food resources.
Although I believe the authors have broken new ground in the study of menopause and long life spans, I have a number of concerns. They are as follows:
- Is that the authors do not pay sufficient attention to distinguishing between whether the route of fitness enhancement is through increased fertility of daughters or survivorship of descendant's or collateral’s offspring. Obviously, food provisioning by grandmothers could achieve either or both ends but the pay-offs might differ strongly under various environmental circumstances.
- I am also a bit concerned that general childcare (baby sitting or child minding) is not discussed. Both of these altruistic acts could have dramatic effects the fertility of a relative or the survivorship of a relative’s children. Alloparental childcare could enhance survivorship and/or fertility in a variety of ways such as to free the mother to forage more efficiently; protect the child from sources of environmental trauma reduce mother’s caloric expenditure (not having to carry the child) and allow her to become fertile more rapidly
- Although the focus is on grandmothers and mothers, the role of the father is not taken into consideration as an independent variable. To what degree do they invest in offspring and how is it conditioned by the availability of his wife’s mother or his mother?
The General Scheme
The data part of the paper consists of seasonal statistics on time allocation, weight changes, and resource acquisition by different age and sex groups. From this they glean the following crucial elements for their model:
- Mother’s foraging and food sharing are crucial to children’s welfare.
- Lactation and carrying costs reduce mother’s foraging ability
- Grandmother’s foraging offsets burden of dependent children
- There is a significant correlation between time non-nursing mothers spend foraging and children’s’ weight changes but no such relationship exists for nursing mothers. The basic pattern shows a reduction in foraging with the birth of an infant and then a slow increase in foraging as the infant ages.
Importantly, grandmothers increase foraging with new grandchild and forage less when they have no nursing grandchildren. This suggests that grandmothers are critical to the survival of grandchildren and/or may enhance their daughter's fertility.
In species where maternal care is crucial to offspring survival, aging mothers are less likely to see final child survive so they might do better by ceasing reproduction to insure that final child survives or invest in children’s offspring. But this alone is not sufficient to cause menopause. The authors speak of an equilibrium between the ability to reproduce and the ability to live long. If reproduction is costly, the cost is longevity. The key to breakage in the equilibrium is the use of a resource that has high return rates for adults but not for children. This would allow an increase in daughter’s fertility rate if the grandmother ceased reproduction while continuing to live.
Implications for Hominid Social Organization
Suggests that mothers and daughters hang together to exploit high extraction effort resources which would reduce feeding competition. Also, preadolescent daughters could be important helpers at the nest. This being so, it is likely that contrary to the standard chimp or "Man the Hunter Model" the social core of the group would be related females and not related males.
Says that men provide little from hunting that would enhance child survivorship. This is because men devote their economic effort to big game hunt. When such game is captured it is widely distributed to all camp members with the hunter's family getting very little of the meat. This activity is regarded by them as a means for men to enhance their status and sexual prospects and it is not a means for providing for a family. Note that this perspective is roundly criticized by a number of the commentators. Furthermore, it is important to note that men gather and it is unclear what role their total acquisition (hunting and gathering) would have for child welfare. They ought to provide data on male labor time when their wives are lactating.
As a consequence of female cooperation and male interest in hunting for status they make the following claim
- “The assumption that nuclear families are fundamental economic units among modern human foragers, let alone ancestral hominids, is due for revision.”
The “grandmother hypothesis” and the Aché
Hill and Hurtado’s demonstration that survivorship and fertility were enhanced by having grandmothers, the effect was not statistically significant which led them to reject the grandmother hypothesis. Hawkes et al. suggest that there are fundamental differences between the Ache and Hadza:
- Aché men supply 85% of the calories. So grandmothers’ effects will be slighter among Ache but stronger among Hadza.
- Hill and Hurtado compared the fertility of women and the survivorship of their children of women with and without mothers. In contrast, Hawkes et al. argue that grandmothers can help son's and other relatives as well as their daughters.
- The Hill and Hurtado model looked at the trade-off between continued reproduction versus investing in those who are already born. They change the issue by assuming that fertility after age ceases and that long life span is the issue to be explained. In other words, “Attention is directed to the trade-off between reproductive effort earlier in life and somatic effort toward increased survivorship at later ages.”
Alvard and Conservation
Although he does not strongly emphasize the difference between opportunism and conservation, he seems to make the the following distinction:
- Conservation has to do with restraint combined with a long-term goal of sustained production. This means that individuals will forgo taking game of certain age or sex groups or avoid taking game in particular areas or at particular times of the year. He largely ignores the issue of game taboos or blanket prohibitions on the taking of particular species and how that may or may not provide evidence for conservation or opportunism.
- Opportunism has to do with attempts to maximize one's instantaneous (short-term) net rate of return while foraging. Importantly, restraint may be involved but only insofar as it leads a hunter to more efficiently (at a higher rate).