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Este Blogue é um estudo da Associação Projecto Raia Alentejana e tem como objectivo a discussão da violência em geral e da guerra na Pré-História em particular. A Arqueologia da Península Ibérica tem aqui especial relevo. Esperamos cruzar dados de diferentes campos do conhecimento com destaque para a Antropologia Social. As críticas construtivas são bem vindas neste espaço, que se espera, de conhecimento.

Guerra Primitiva\Pré-Histórica
Violência interpessoal colectiva entre duas ou mais comunidades políticas distintas, com o uso de armas tendo como objectivo causar fatalidades, por um motivo colectivo sem hipótese de compensação.


Tuesday, 9 March 2010

THE EVOLUTION OF HUMAN AGGRESSION: LESSONS FOR TODAY'S CONFLICTS

Presentation Abstracts
Keynote 1
Destined to Wage War Forever? The Evolution of Peacemaking Among
Primates.
Frans B. M. de Waal
Living Links, Yerkes Primate Center, Emory University

Following the Second World War, scientists were naturally fascinated with the
aggressive "instinct" in humans and animals. In the 1970s, evolutionary biology
added the view of animal social life as an arena of competition. At about the
same time, however, primatologists began to emphasize long-term social
relationships. The discovery of reconciliation behavior came out of this tradition,
confirming the impression that societies constitute a balancing act between
cooperation and competition. Reconciliation - defined as a friendly reunion
between former opponents - has since been confirmed in many different species,
in both captivity and the field, both experimentally and observationally.
Chimpanzees, for instance, kiss and embrace after a fight. Reconciliation has also
been demonstrated in non-primates, such as dogs and dolphins. This behavior
truly serves what its name suggests, i.e. to repair social relationships. The
dominant idea (known as the Valuable Relationship Hypothesis) is that
reconciliation will occur whenever parties stand much to lose if their relationship
deteriorates. This means that peacemaking depends on overlapping interests, a
situation common within but rare between primate groups. In our own species,
however, interdependencies between groups or nations are not unusual, and in
fact increasing, making for applicability of these models to international
relations.
Panel 1: Conflict and Conflict Resolution among Great Apes.
The imbalance-of-power hypothesis and the evolution of war.
Richard Wrangham
Harvard University

Among vertebrates, lethal intergroup aggression has traditionally been regarded
as being unique to humans, and human warfare has therefore been widely
interpreted as an evolutionary aberration due to social construction. The
discovery since the 1970s that chimpanzees kill adult members of neighboring
social groups has challenged the social construction hypothesis. Here I review
the imbalance-of-power hypothesis, which states an evolutionary history of
communal territoriality combined with fission-fusion grouping favors the
tendency to kill rivals when the costs are perceptibly low. Current data on
chimpanzees, bonobos and other mammals support the imbalance-of-power
hypothesis and suggest that in certain species natural selection has favored a
drive to dominate neighboring communities through attempts to kill. I suggest
that the imbalance-of-power hypothesis also provides a useful basis for
understanding intergroup violence in small-scale human societies, but that it
needs to be modified to take account of human-specific attributes such as reward
systems and political complexities. The proposal that human intergroup
aggression has its evolutionary origins in an imbalance-of-power system means
that violence will emerge predictably when groups have sufficient power, but
that violence is suppressed in conditions without intense power imbalances.
Evolutionary Perspectives on Conflict Resolution
Joan B. Silk
Department of Anthropology and Center for Society and Genetics, University of
California, Los Angeles

Sociality is favored by natural selection because it makes animals safer from
predation or enables them to collectively defend access to resources. At the same
time, living in close proximity to conspecifics can lead to conflicts of interest and
competition. In a number of animal taxa, including many nonhuman primate
species, evolution has favored an effective mechanism for resolving conflicts
with group members: they engage in peaceful contacts with former opponents in
the minutes that follow conflicts. There is a broad consensus that these
reconciliatory interactions relieve the stressful effects of conflict and permit
former opponents to interact peacefully, but less consensus about their adaptive
function. Primates may reconcile to obtain short term objectives, such as access
to desirable resources. Alternatively, reconciliation may preserve valuable
relationships damaged by conflict. Some researchers view these explanations as
complementary, but they generate different predictions about the patterning of
reconciliation that can be partially tested with available data. There are good
reasons to question the validity of the relationship-repair model, but it remains
firmly entrenched in the reconciliation literature, perhaps because it fits our own
folk model of how and why we resolve conflicts ourselves. It is possible that the
function of reconciliation varies across taxa, much as other aspects of cognitive
abilities do.
Chimpanzee Politics: Pacifying Interventions and Reconciliation
Frans B. M. de Waal
Living Links, Yerkes Primate Center, Emory University

Chimpanzee males form coalitions within the group in pursuit of high rank.
These coalitions are formed opportunistically, and may involve high risk,
including fatal aggression. High ranking males perform a control role in that
they break up fights among others. This behavior has group-wide repercussions
as demonstrated in an experiment on a different species. Flack et al. (2005)
removed control males from a large captive macaque group for brief periods of
time, and each time measured a deterioration of social relationships in the
remainder of the group, including a sharp drop in reconciliation behavior.
Reconciliation, which has been demonstrated in a great variety of primates and
other animals, affects stress levels, social tolerance, and long-term social
relationships, hence is an essential component of group harmony.
Sexual dimorphism and aggression in primates: just where do humans fit in?
Michael Plavcan
Anthropology, University of Arkansas

Male primates are often much larger than females, and equipped with large
canine teeth (dimorphic). Humans, on the other hand, show comparatively
modest differences in body size, and lack large canine teeth. These characters are
often associated with monogamy and affiliation in humans. However,
comparative analyses more closely tie dimorphism with degrees of intra-sexual
aggression and differences in reproductive success among males. The closest
relatives of humans – the great apes – show a gradation of dimorphism that
appears to track the degree of relatedness to humans. Gorillas and orangutans
are intensely dimorphic, and chimpanzees much less so. Many models for the
evolution of human behavior use chimpanzees as an analogue for an ancestral
condition. But data from the fossil record strongly contradict this assumption,
suggesting that behavioral similarities between chimpanzees and humans
associated with reduced dimorphism evolved in parallel, and that modern
humans are derived independently from a strongly dimorphic ancestor. This has
important implications for understanding whether human patterns of aggression
and affiliation represent an inherited condition, or have separately evolved as
part of a unique human adaptation.
Keynote 2
Nothing to Lose? Economic Inequality, Poor Life Prospects, and Lethal
Competition.
Martin Daly & Margo Wilson
Department of Psychology, McMaster University

The majority of homicides are the culminations of competitive confrontations
between young men, and the immense variation in homicide rates is primarily
due to the variable incidence of such contests. The most successful predictor of
homicide rates has proven to be the intensity of economic competition, as
indexed by income inequality. But which particular men are at risk? In large
measure, it is those whose lives are going nowhere unless they escalate their
competitive tactics.
Thinking about homicide in this way has led us to a number of discoveries about
its demography and epidemiology, which we will review. We will also address
the questions of why homicide rates declined in much of the developed world in
recent decades although income inequality was on the rise, and whether crosscultural
variability in attitudes and values provides an alternative to economic
explanations for the remarkable variability in homicide rates between and within
nations.
We do not suggest that killing per se can be understood as either rational or
fitness-promoting. Homicides are relatively rare dénouements of hostile
confrontations, and it is in the modulation of men’s willingness to engage in
risky competition that adaptation should be sought.
Panel 2: Coalitionary Violence and Warfare
A History of Violence
Steven Pinker
Harvard College Professor and Johnstone Family Professor, Department of
Psychology, Harvard University

Contrary to the popular impression view that we are living in extraordinarily
violent times, rates of violence at all scales have been in decline over the course
of history. I explore how this decline could have happened despite the existence
of a constant human nature.
Americans at War: Evolutionary Perspectives on an Age Old Story
Patricia M. Lambert, Utah State University

The archaeological record of North America is rife with evidence for war, both
prehistoric and historic. Ancient palisade lines, cliff dwellings, towers,
entrenchments, burned villages, no-man’s-lands, war weapons, and war dead
attest to a history of conflict extending far back beyond the arrival of Europeans
and the establishment of the United States. These remnants of the past are
fascinating, insightful, and historically important—but are they relevant to the
topic of conflict management in the 21st century? The purpose of this paper is to
explore the value of this longitudinal record for revealing the larger causal forces
that underlie intergroup conflict, forces that are often masked in the modern
world by proximate triggers such as hotel bombings and suicide attacks, and
thus difficult to identify. History has shown us that conflict resolution is a
challenging endeavor, but those efforts that take underlying causation into
account may have a better chance of resolving today’s conflicts and heading off
those that threaten our collective future.
Male Hierarchies, Parent-Offspring Conflict, and Warfare in Papua New
Guinea
Polly Wiessner
Anthropology, University of Utah

Population growth and the increase of young men in proportion to older men are
associated with accentuated coalitional violence worldwide. Here I will propose
that an extension of parent-offspring conflict provides a powerful framework for
understanding the course of coalitional violence. Older men seek to manipulate
inter-group competition to provide optimal resources and security for their
offspring and those of their close collaterals. In contrast, young men seek to
demonstrate physical prowess and willingness to sacrifice for the group to reap
individual reputation and rewards. In periods of demographic or technological
stability, older men with control of resources, knowledge, and networks prevail.
With rapid change, younger men are able to disrupt the male power hierarchy,
generating chaos.
I will draw on a case study from the Enga of Papua New Guinea to illustrate how
parents parent/offspring conflict is played out in the context of warfare in precolonial
and modern times young men in the driver’s seat, and what older men
are doing about it.
Panel 3: Further Discussion of Coalitionary Warfare
Warfare and Human Ultrasociality
Peter Turchin
Ecology and Evolution, University of Connecticut

How did human ultrasociality - extensive cooperation among large numbers of
unrelated individuals - evolve? What are the social forces that hold together
complex societies encompassing hundreds of millions of people? Using
theoretical insights from models of multilevel selection I argue that there is a
fundamental connection between human ultrasociality and warfare. It was
intergroup conflict that generated selective pressures for increasing scale and
complexity of human societies. I illustrate this social evolutionary dynamic with
two examples. The first is the rise of historical megaempires on the frontiers
between settled farmers and nomadic pastoralists. The second one is the
transformative influences of the Indian Wars on the European settlers in North
America.
From Lab to War: The Role of Biology and Psychology in Political Aggression
Dominic D. P. Johnson
Politics & International Relations, University of Edinburgh

I present results from a series of laboratory experiments demonstrating that
human biology and psychology have significant influences on the probability of
aggression. In interactive war-game experiments over networked computers, we
found that: (1) men (not women) were over-confident about winning, and those
who were more over-confident were more likely to attack their opponents; (2)
second-to-fourth finger length ratios (2D:4D), a possible biomarker of pre-natal
testosterone exposure, also predicted the probability of attacking. In our most
recent experiments, we found that: (3) behavioral aggression (willingness to
inflict harm on others) was significantly associated with MAO-A (monoamine
oxidase A) gene, especially in response to provocation. Finally, in hypothetical
international crisis scenarios, levels of aggression in subject’s chosen policy
options (which ranged from withdrawal, to negotiation, to military attack) were
significantly predicted by: (4) political partisanship (Democrat-Republican
affiliation, and a general liberal-conservative scale); and (5) subjects’ confidence
that their chosen policy would succeed. I conclude by arguing that physiological
and psychological influences on aggression were adaptive in our evolutionary
past because they promoted survival and reproductive success. However, these
same mechanisms are often costly and maladaptive in today’s very different
social and political environment. If we ignore the biological bases of aggression,
we will only make the task of prediction and prevention harder.
Panel 4: Hormones and Human Dominance and Aggression
The challenge of testosterone
John Archer, Department of Psychology,University of Central Lancashire

Chronic high levels of testosterone exert evolutionary costs. A common response
to this is in males of many species is to have a neuroendocrine system that is
responsive to situations that require high testosterone levels rather than
maintaining consistent high levels. Evidence from studies of testosterone and
behavior in humans is assessed in relation to whether human males fit this
pattern. It is concluded that they do, and also that there are individual
differences associated with testosterone levels indicative of specialization for
mating or parental effort.
Ontogeny of hormonal mechanisms for coalitionary aggression
Mark Flinn
University of Missouri, Columbia

Humans have an unusual suite of traits, including: (1) extensive male parental
effort, (2) relatively exclusive, long term mating relationships, (3) mutual respect
for other males’ mating relationships, (4) communities composed of many males
from multiple kin groups, (5) inter-community aggression, and (6) a long period
of juvenile dependence. The neurological and hormonal mechanisms that
underpin this unique suite of behavioral traits are uncertain, but may provide
important clues about the selective pressures that guided human evolution.
Here I present data from a 20-year study of a rural community on the island of
Dominica. Testosterone and cortisol response to competitive events among adult
males within a coalition are different than responses among males from different
coalitions. Similarly, adult males have different hormonal responses to females
that are attached to close friends than to unattached females, or females attached
to males that are not close friends. We are currently studying the ontogeny of
these distinctive hormonal responses. During middle childhood, boys and girls
show behavioral differences in play and social interactions: boys tend to invest
more time in organizing groups of peers, among which they form hierarchies,
and compete with other groups. Conversely, girls usually invest more time in
dyadic interactions with similar age girls, caring for siblings, and doing domestic
chores. How the onset of male coalitional and female dyadic psychobiology and
life history trajectories are related to social events is yet an open question. We are
examining the onset of adrenarche, pubarche, and individual differences in
DHEA (Dehydroepiandrosterone) production using semi-structured, long
interviews and a competitive enzymatic immunoassay of saliva samples. Peer
network density is assessed by multidimensional scaling (MDS), with the
hypothesis that it is denser for boys than for girls. Everyday social interactions
are coded from observations and video. Analyses suggest that middle childhood
and the unusual temporal patterning of adrenarche are important components in
the ontogeny of coalitionary behavior.
The role of physical strength in anger and anger expressions
Aaron Sell
Center for Evolutionary Psychology, University of California, Santa Barbara

Anger can be understood as a cognitive mechanism designed by natural selection
to negotiate conflicts of interest in ways similar to, but distinct from, non-human
animal conflict. Using an evolutionary biological framework, one can ask under
what conditions aggression is mobilized by the anger system, and predict
individual differences in thresholds for aggression. For example, because
physical aggression was frequently used by men during our evolutionary history
to negotiate conflicts of interest, it was predicted and found across different
cultures that physically stronger men were more prone to anger. Similarly,
physical changes to the face, body, and voice preceding aggression can be
understood as displays designed by natural selection to enhance signals of
physical strength and fighting ability.
Panel 5: Domestic Violence, with Emphasis on Spousal/Partner Relationships
An evolutionary perspective on family violence
John Archer
School of Psychology, University of Central Lancashire,

The aim of this presentation is to evaluate the application of evolutionary
principles to the understanding of family violence. The following relevant
evolutionary principles will be outlined: kinship and inclusive fitness; paternity
uncertainty and mate guarding; reproductive value; parent-offspring conflict;
resource holding power. The motivational mechanisms underlying these
principles are then discussed, specifically discriminative parental solicitude and
kin resemblance. The following forms of family violence are presented in the
light of these principles and mechanisms, with relevant empirical research: (1)
parental violence to unrelated children; (2) parental violence to biological
children; (3) offspring’s violence to parents; (4) violence between siblings.
Violence between sexual partners is considered in relation to (1) conflicts of
interest and power relations between males and females; (2) spousal abuse as
mate guarding; (3) male sexual jealousy as a mediator of partner violence; (4)
reproductive value. It is concluded that an evolutionary approach has a number
of strengths in terms of providing a comprehensive theoretical framework and
specific principles underlying many aspects of family violence, although the
current emphasis on male mate guarding is too narrow to explain current
findings in relation to partner violence.
Men’s Proprietary View of Their Romantic Partners is Specific to Sexuality:
An Experimental Study
Aaron T. Goetz
California State University, Fullerton

Even across disciplines and theoretical perspectives, most agree that men take a
proprietary view of their romantic partners; men view their partners as an entity that they
privately own and control. Disagreement, however, arises over the extent of this
proprietary view. Some theorists have argued that men attempt to control and dominate
all aspects of their partners’ lives, while others—particularly those taking an evolutionary
approach—have argued that men’s proprietary view of their romantic partners is specific
to sexuality. Here, I describe the results of a recent experimental study in which I
demonstrated that men are less likely to tolerate their partner’s participation in activities
that more likely to lead the opportunity for infidelity and that men become more tolerant
of their partner’s participation as the activities become less related to the opportunity for
infidelity. These results suggest that men afford their partners many freedoms with the
exception of those related to their sexual behavior. Discussion addresses how the
adaptive problem of paternity uncertainty plays a central role in intimate partner violence.
Hurting the ones we love: The features and functions of aggressive
punishment in close relationships
Julie Fitness
Macquarie University,

Human beings are born with a fundamental need for attachment, intimacy, and
the love and esteem of valued others. Close relationships, then, are the source of
our most intense positive emotions, including love and joy. However, close
relationships are also the source of intense pain and anger when relationship
partners reject or hurt one another, or fail to meet one another’s needs, desires, or
expectations. Further, the experience of emotional pain may generate a powerful
impulse to punish, or inflict pain upon, the person who appears to have caused
the distress. In this paper I will argue that the urge to retaliate in response to
partner-triggered emotional pain is, to an extent, hard-wired and serves a variety
of potentially adaptive functions, though it may also have destructive and tragic
consequences. Following a discussion of the features and functions of
punishment in close relationship contexts from an evolutionary, socialpsychological
perspective, I will discuss the roles of emotional pain and
punishment as it relates to domestic violence. I will then present the findings of
an empirical study of aggressive punishment in marriage and suggest some
implications of this work for both enhancing our understanding of aggression in
close relationships, and preventing its occurrence.
Panel 6: Further Discussion of Domestic Violence, with Emphasis on Parent-
Child Relationships
Violence against Stepchildren. The Evidence and its Discontents.
Martin Daly and Margo Wilson
Department of Psychology, McMaster University

Parental investment is costly and evolves to be allocated where it is most likely to
promote parental fitness. While it is implausible that abusing or killing
stepchildren would have promoted the assailants’ fitness in ancestral human
social environments, a general preference for their own offspring surely would
have. Elevated risks to stepchildren are a likely byproduct of such discriminative
parental solicitude.
It is now almost 30 years since we first demonstrated that children living with
one genetic parent and one stepparent were indeed mistreated more than
children in intact birth families. Further research has shown that such
“Cinderella effects” are widespread, perhaps even universal, are often
substantial, and cannot be explained away as artifacts of any correlated factor yet
suggested.
The disproportionate victimization of stepchildren is now the most extensively
documented generalization in the family violence literature, raising further
questions, such as what explains variability in risk differentials between
maltreatment types and locales, and whether the individual-level predictors of
abuse are the same for genetic and stepparents. Unfortunately, progress on these
important issues has been hindered by a relentless distraction: the manufacture
of “controversy” about whether Cinderella effects exist at all. A motivation for
this nay-saying appears to be antipathy to the Darwinian worldview and/or to
its application to Homo sapiens.
Hormonal responses to domestic violence
Mark Flinn
University of Missouri, Columbia

Exposure to stressful experiences increases vulnerability to adverse health
outcomes. A potential endocrine mechanism mediating the link between stress
and health is the hypothalamic-pituitary-adrenal (HPA) system, with a key role
attributed to the glucocorticoid hormone cortisol. Retrospective clinical studies
indicate that traumatic experiences during childhood such as exposure to
domestic violence can have a permanent influence on HPA regulation. Here I
present analyses of naturalistic, longitudinal data on cortisol levels, social
stressors including domestic violence, and health among children to assess
developmental trajectories of HPA functioning. Saliva samples (N=32,219) were
collected and assayed for cortisol in concert with monitoring of growth,
morbidity, and social environment for children (N=317) in a rural Dominican
community each year over a 20-year period (1988-2008). Several measures of
individual cortisol (C) profiles are analyzed: (1) average C, (2) average wake-up
C, (3) average ratio of AM/PM C, (4) variability of AM and PM C, and (5)
reactivity of C in response to stressors. A majority of children exhibit moderate
stability of all five measures over multiple year periods. Children exposed to
domestic violence exhibit significant changes in some of these measures.
Changes in HPA response, however, appear to be context-specific, with
increased reactivity to some types of social stressors, but normal or reduced
reactivity to physical stressors.

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