Lecture Coverage: Week by Week

Week 8 (14-16 October): Time Allocation and Tropical Foraging 

• The Lotka-Volterra Model of Population Growth

Human responses to environmental resistance include:

1. labor intensification
2. reduction in quality or quantity of diet
3. migration
4. innovation of new food production techniques

• Foraging in the Tropics

Foraging in the tropics is impossible or difficult because:

1. biomass is mainly trunks and roots with only 2% leaves and even less edible biomass
2. distribution of useful resources is both patchy and dispersed
3. resources are high in trees and costly to acquire
4. processing costs may be high because of woody coverings and high levels of toxins
5. most animals are lean, therefore provide poor caloric resources which may stress the body (Speth and Spielman) with high levels of nitrogen and costly digestion (specific dynamic action)
6. seasonality is sufficient to cause problems in availability of plant resources
7. high species diversity leads to lack of a staple

Why Live in a Group?
There are a number of specific reasons for group living which include:

1. Predation pressure or warfare

2. Economies of scale which include a variety of factors such as:

• sharing to reduce variance in food consumption
• information sharing about the location of resources
• cooperation in the pursuit and capture of game

3. Mating purposes

4. Social insurance or the ability to assist others because they are ill or injured

5. A superabundance of resource.

The "Prisoner's Dilemma": stability and instability in the evolution of cooperation.

Definitions of the prisoner's dilemma:
 The order of payoffs

• Can't get of the dilemma by exploiting one another.  Therefore, the average of sucker's payoff and temptation to defect (2.5) is less than the average of cooperation.  That is, you can't take turns exploiting one another.
• The outcome holds only for those games with a known finite number of rounds.  Further, one may interact with a variety of individuals but it is done one at a time and individuals recognize and recall the previous behaviors of interactants

• If game is finite then no incentive to cooperation since one can gain on the last move (t=5).  (For example, buying a used car from a dealer versus a neighbor).
• If game is infinite in duration then advantages of cooperation emerge, since no last move temptation to defect does not exist.
• Players may not make enforceable threats or commitments since no central authority exists to control situation.
• There is no way to know what a player will do on the next move.  So no strategies such as "do what the other is about to do".
• No way to run away form or eliminate competition.  Must face up.
• No way to change payoffs.
• They can only communicate by virtue of previous actions

A variety of solutions were submitted by experts (game theoreticians, evolutionary biologists, political scientists, and mathematicians) and the winning strategy turned out to be "tit-for-tat".  The rule is played as follows: the first time you meet an opponent, cooperate.  The second time you meet do what ever the opponent did to you the last time you met.  This strategy, like many of the high ranking strategies had the following characteristics that made it difficult to beat:

Tit for tat wins because it has the  following attributes:

•  It avoids unnecessary conflict (i.e. it is nice as were most high scoring entries);
•  It has  provocability in the face of uncalled defection;
•  Forgiveness (will resume cooperation if previously defecting opponent cooperates)
•  Clarity (it is a simple strategy that is easy to understand).

Please recall that we first explored the phylogenetic model of territoriality by reviewing the approaches of Dart and Lorenz.  These crudely deterministic models assumed no environmental input influencing the decisions made by organisms.  The modern evolutionary biology approached developed by Jerram Brown and applied to the human situation by Dyson-Hudson and Smith assumes that humans are sensitive to the costs and benefits of territorial defense.  Later, Kelly explores the work of Cashdan's social boundary defense as a special application of the Brown and Dyson-Hudson and Smith cost benefit model.

Week 11 (11/4/97) The problem of infanticide  

The time honored approach among anthropologists is to assume that infanticide is one of several  population regulation mechanisms designed to prevent hunter-gatherers from depleting environmental resources or degrading their environment.  From this perspective, infanticide is a way to maintain the balance between people and the resources they exploit.  With the influential publication of Susan Lees' and Daniel Bates' "The Myth of Population Regulation", some anthropologists now view infanticide as a mechanism to maximize the reproductive success of individuals (and not the stability of groups).  Bear in mind, we discussed a variety of so-called "population regulation" mechanisms (invalidicide, senilicide, abortion, and post-partum taboos).  However, we gave special attention to Daly and Wilson's crosscultural research on infanticide to suggest that such mechanisms actually insure the quantity and quality of children and the decision to commit infanticide is made by the parents and not the group:

Consistent with evolutionary theory, Daly and Wilson predict that infanticide should occur under the following conditions:

1. uncertain paternity
2. defects in offspring
3. lack of parental resources to successfully rear the child

Of the 112 reasons, 97 or 86% fell into the evolutionary explanations posited by Daly & Wilson.

Reason 1: Is the infant the offspring of the mother's current husband?
Number of instances                    20 (17% of total)

Breakdown:

Adulterous conception                15
Non-tribal sire                              3
Sired by mother's first husband      2

Reason 2:  What is the infant's quality, and hence its ability to convert parental assistance into eventual fitness?
Number of Instances             21 (19% of total)
 
Infant deformed or very ill      21

Reason 3:   Are present circumstances favorable for child rearing?

Number of Instances             56 (50% of total)
 
Twins                                                    14
Birth too soon or too many children        11
No male support                                    6
Quarrel with husband                             1
Mother died                                           6
Mother unwed                                       14
Economic hardship                                  3
Wrong season                                         1
 
 
 
Week 12 (11/13/96) Demography 

In many cases, infanticide appears to have a sexual bias with preferential female infanticide appearing to be the most common.  Hewlett suggests that preferences of one sex over the other may be a consequence of the value of that sex in subsistence activities.  That is, the sex that contributes least to subsistence is more likely to killed at birth.  Although we don't have actual measures of infanticide rates for any groups (exceptions would be Bugos and MacCarthy on the Ayoreo and Rasmussen on the Ekimo), Hewlett used juvenile sex ratios (ages 1-15) and economic emphasis to test this idea.  Below in graphical form is a test of his hypothesis.

Hewlett demonstrates that when male contributions to the diet are low they are more likely to be victims of infanticide or neglect and when female contributions to the diet are slight they are more likely to be the victims of infanticide or neglect.

Week 12 (11/15/97)  The Division of Labor

There are three non-mutually exclusive explanations of the sexual division of labor.  They are:

1. Strength and endurance differences between the sexes
2. Brown's model of childcare constraints
3. The chaining or linkages model of Burton and White

It is suggested here that the degree to which women participate in subsistence activities depends upon the compatibility of the latter with simultaneous child-care responsibilities.  Women are most likely to make a substantial contribution when subsistence activities have the following characteristics:

• the participant is not obliged to be far from home;
• the tasks are relatively monotonous and do not require rapt concentration;
• and the work is not dangerous, can be performed in spite of interruptions, and is easily resumed once interrupted.

• High fertility
• Long-term and on-demand nursing
• High levels of active care to safeguard children in a dangerous environment

Week 13: Cultural Evolution (11/29/97)

During this week we dealt with the materials presented in Kelly's final chapter about the evolution of inequality and social complexity.  Please refer to the notes on Chapter 8.

Female Reproductive Cancers:  A Case for Mismatch Theory.

Reproductive cancers (endometrial, breast, and ovarian) are virtually unheard of in foraging societies yet they are common and becoming moreso in modern societies.  It has been suggested by a number of researchers that the greatest risk factor women have for getting a reproductive cancer is the degree to which their reproductive careers differ from hunter-gatherer women.  Some of the following are: age at first birth, number of children, and duration and intensity of lactation.  The table below demonstrates the relevant reproductive contrasts:

Othe risk factors include total fat and dietary fiber intake, obesity, and aerobic conditioning.  In each of these case the values for modern women differ from hunter-gatherer women in ways that increases the likelyhood of cancer.  The degree of risk of reproductive cancers of hunter-gatherer women compared to modern women is expressed in the table below:

The abbreviation "COC" stands for combined oral contraceptive (combination of estrogen and progestoren) which provides some protection against certain reproductive cancers.