LeadershipFollowershipandEvolution.pdf

Leadership, Followership, and Evolution
Some Lessons From the Past

Mark Van Vugt University of Kent
Robert Hogan Hogan Assessment Systems

Robert B. Kaiser Kaplan DeVries Inc.

This article analyzes the topic of leadership from an evo-
lutionary perspective and proposes three conclusions that
are not part of mainstream theory. First, leading and
following are strategies that evolved for solving social
coordination problems in ancestral environments, includ-
ing in particular the problems of group movement, intra-
group peacekeeping, and intergroup competition. Second,
the relationship between leaders and followers is inher-
ently ambivalent because of the potential for exploitation of
followers by leaders. Third, modern organizational struc-
tures are sometimes inconsistent with aspects of our
evolved leadership psychology, which might explain the
alienation and frustration of many citizens and employees.
The authors draw several implications of this evolutionary
analysis for leadership theory, research, and practice.

Keywords: evolution, leadership, followership, game the-
ory, mismatch hypothesis

Why is leadership important? During times ofpeace and prosperity, it seems not to matter.However, when politicians start wars, when
business leaders gamble with our life savings, and when
religious leaders create violent sectarian divides, leadership
becomes a matter of life and death.

We know a lot about leadership (Bass, 1990; House &
Aditya, 1997; Yukl, 2006). It is a universal feature of
human societies and affects the quality of life of citizens in
important ways (Brown, 1991; R. Hogan, Curphy, &
Hogan, 1994). When people are placed in ad hoc laboratory
groups, leader–follower structures quickly emerge (Bales,
1951; Mann, 1959; Van Vugt & De Cremer, 1999). Hu-
mans easily recognize leadership potential in others (Lord,
DeVader, & Alliger, 1986). People also romanticize lead-
ership; we often attribute great importance to leaders even
when it is not warranted (Hackman & Wageman, 2007;
Meindl, Ehrlich, & Dukerich, 1985). Leadership is an un-
avoidable theme in society and arguably the most important
problem in the social sciences.

Although the leadership literature is enormous, it
lacks an integrative theoretical framework that can make
sense of the richness of the data (Chemers, 2000; R. Hogan
& Kaiser, 2005). There are several reasons for this. First,
the literature contains many useful mid-level theories that
are not very well connected (Bass, 1990; Yukl, 2006).

Second, the literature focuses on leaders and tends to
ignore the essential role of followers (Hollander, 1992;
Yukl, 2006). Third, research largely concentrates on prox-
imate issues of leadership (e.g., What makes one person a
better leader than others?) and rarely considers its ultimate
functions (e.g., How did leadership promote survival and
reproductive success among our ancestors?) (R. Hogan &
Kaiser, 2005). Finally, there has been little cross-fertiliza-
tion between psychology and disciplines such as anthro-
pology, economics, neuroscience, biology, and zoology,
which also contain important insights about leadership
(Bennis, 2007; Van Vugt, 2006).

This article offers a view of leadership inspired by
evolutionary theory, which modern scholars increasingly
see as essential for understanding social life (Buss, 2005;
rence & Nohria, 2002; McAdams & Pals, 2006; Nettle,
2006; Schaller, Simpson, & Kenrick, 2006). We argue first
that an evolutionary approach to leadership raises some
important new questions. Next we analyze the implications
of leader–follower relations in early human and nonhuman
societies for theories of leadership. We use (evolutionary)
game theory to model the emergence of leadership; this
model is followed by a hypothetical account of how lead-
ership developed over four stages of evolutionary history.
We conclude with some novel implications of this analysis
for leadership theory, research, and practice.

An Evolutionary Analysis of
Leadership
Researchers define leadership in many ways (Stogdill,
1974). We define it broadly in terms of (a) influencing
individuals to contribute to group goals and (b) coordinat-

Mark Van Vugt, Robert Hogan, and Robert B. Kaiser contributed equally
to this article.

We are indebted to Rob Kurzban for his intellectual input and to
Robin Dunbar, Dominic Johnson, Muhammad Ghufran Ahmad, and Peter
Richerson for their comments on previous versions. We also acknowledge
constructive criticism from William C. Howell.

Correspondence concerning this article should be addressed to
Mark Van Vugt, Department of , University of Kent, Can-
terbury CT2 7NP, United Kingdom; Robert Hogan, Hogan Assessment
Systems, 2622 East 21st Street, Tulsa, OK 74114; or Robert B. Kaiser,
Kaplan DeVries Inc., 1903-G Ashwood Court, Greensboro, NC 27455.
E-mail: [email protected], [email protected], or rkaiser@
kaplandevries.com

182 April 2008 ● American Psychologist
Copyright 2008 by the American Psychological Association 0003-066X/08/$12.00

Vol. 63, No. 3, 182–196 DOI: 10.1037/0003-066X.63.3.182

ing the pursuit of those goals (cf. Bass, 1990; Hollander,
1992; Yukl, 2006). We think pragmatically of leadership as
building a team and guiding it to victory (R. Hogan et al.,
1994). Leadership is both a resource for groups and an
attribute of individuals, but we believe that its primary
significance concerns group performance (R. Hogan &
Kaiser, 2005; Kaiser, Hogan, & Craig, 2008). Given the
fitness and reproductive benefits associated with social
status (Betzig, 1993; Buss, 2005; Chagnon, 1997), the
“selfish-gene” view of evolution (Dawkins, 1976) suggests
that everyone should strive to become a leader. From this
same perspective it is not obvious why some would vol-
untarily subordinate themselves. Researchers rarely con-
sider the origins of followership, but the topic is central to
an evolutionary analysis.

Although Sigmund Freud, William James, William
McDougall, and E. L. Thorndike were enthusiastic Dar-
winians, evolutionary thinking fell out of favor in main-
stream psychology for most of the 20th century (Pinker,
2002). It is now returning in the form of evolutionary
psychology. Evolutionary psychology proposes that the
mind is composed of mechanisms, called psychological
adaptations, that were favored by natural selection because
they solved adaptive problems faced by our ancestors.
Examples of such mechanisms include mating strategies,
cheater detection, status sensitivity, and language (Barkow,
Cosmides, & Tooby, 1992; Buss, 2005; Schaller et al.,
2006; cf. Darwin, 1871).

Evolutionary psychologists use Tinbergen’s (1963)
four functions model to analyze psychological adapta-
tions. This framework first asks about the proximate
functions of a mechanism. For leadership we can ask
what kind of people make good leaders, a question that
interests social, industrial/organizational, and applied

psychologists. The second question concerns ontogene-
sis: When do leader–follower patterns emerge in the life
span? Does developmental history predict leadership
propensity? Developmental, personality, and educational
psychologists are interested in these issues. The third
question concerns phylogenesis: When did leadership
emerge in our species, and are there parallels in other
species? This question concerns comparative psycholo-
gists, anthropologists, and zoologists. Finally, there is
the question of the ultimate (evolutionary) functions of a
mechanism, a question that interests evolutionary psy-
chologists and biologists: Did leadership promote the
survival of our forebearers so that it became part of our
evolved psychology?

Each of Tinbergen’s (1963) functions analyzes lead-
ership from a different perspective and should be kept
distinct. For instance, functional theories assume that lead-
ership involves identifying obstacles between groups and
their goals and then finding ways to overcome those ob-
stacles (Hackman & Walton, 1986; Lord, 1977). These
theories offer proximate explanations for why particular
leaders are effective in particular circumstances. They can
be complemented with an analysis of the functions of
leadership in ancestral environments, which may explain
why and how the role of leadership evolved in the first
place.

Human Evolution, Group Life, and
Leadership
Humans evolved as group-living animals (Baumeister &
Leary, 1995; D. T. Campbell, 1975; Darwin, 1871). The
genus Homo is estimated to be about 2.5 million years old,
and for most of their existence, hominids lived in small,
kin-based bands on the African savannah, adopting a no-
madic hunter-gatherer lifestyle. Group living allowed our
ancestors to cope with an environment well supplied with
predators but poorly supplied with shelter, water, and food
(Foley, 1997; E. O. Wilson, 1975). Collective foraging and
hunting, food sharing, division of labor, group defenses,
and communal parenting provided a buffer against external
threats (Kenrick, Li, & Butner, 2003). The need for collec-
tive action raises the question of how individuals in social
groups decide what to do and how and when to do it. For
example, finding food would require group members to
decide on the location and timing of foraging activities
(Couzin, Krause, Franks, & Levin, 2005). Such problems
can be solved by a decision-making process in which one
individual takes the initiative and provides direction while
others acquiesce and follow that direction.

Individual and group survival would also have de-
pended on cooperative effort and group cohesion (Bloom,
2000; Darwin, 1871; Sober & Wilson, 1998), which are
inversely related to group size (Dunbar, 2004; Ingham,
Levinger, Graves, & Peckham, 1974). Anthropological ev-
idence suggests that life in ancestral groups involved con-
stant conflict, and homicide was common (Chagnon, 1997;
Knauft, 1987; Wrangham & Peterson, 1996). The need for
peacekeeping created a niche for individuals who, with the
support of the group, intervened in conflicts before they

Mark
Van Vugt

183April 2008 ● American Psychologist

consumed the rest of the group (Boehm, 1999; de Waal,
1996).

Conflict and warfare between groups was a major
force in human evolutionary history (Alexander, 1987;
Bloom, 1997; Chagnon, 1997; Diamond, 1997; Keeley,
1996; Van Vugt, De Cremer, & Janssen, 2007; Wade,
2006; Wrangham & Peterson, 1996). Intergroup competi-
tion may have created pressures for the evolution of a range
of groupish traits such as altruism (Axelrod, 1984), empa-
thy (Preston & de Waal, 2002), morality (de Waal, 1996;
Haidt, 2007), social identity (D. T. Campbell, 1965), and
perhaps leadership. Darwin (1871, p. 132) noted, “A tribe
including many members who . . . were always ready to aid
one another, and to sacrifice themselves for the common
good, would be victorious over most other tribes, and this
would be natural selection.” Deferring to a central com-
mand enhances group performance during intergroup con-
flict (Keegan, 1994; Sherif, 1966), creating a role for lead-
ership.

Thus, leadership probably has a long evolutionary
history. It may have emerged as a solution to specific group
coordination challenges— group movement, intragroup
conflict, and intergroup competition are prime candidates.
Arguably, individual fitness would be enhanced by living
in groups with effective leadership. As a test of Darwin’s
(1871) observation, imagine two groups of early humans
living in the same region and competing for the same
resources. One group is characterized by poor group deci-
sion making and internal discord. The second is character-
ized by efficient group decision making and internal cohe-
sion. Over time, the second group will prevail. In this way,
psychological mechanisms supporting leadership and fol-
lowership could eventually spread through a population.

Adaptations Supporting Leadership and
Followership

A computational analysis of the coordination problem pro-
vides clues to the cognitive processes needed to support
leadership (cf. Cosmides & Tooby, 1992; Pinker, 2002).
The simple decision rule “follow the leader” can be broken
down into several components. First, individuals must per-
ceive the need for coordination. In emergencies, people
coordinate spontaneously (Argote, 1982), which suggests
that humans may have specialized mechanisms for identi-
fying situations requiring coordination. Second, situations
in which threats are not obvious (e.g., a slow decline of
resources) or are novel (e.g., climate change) require mech-
anisms that allow people to plan ahead and anticipate new
dangers, which suggests a role for general intelligence
(Kanazawa, 2004). Third, individuals must decide on a
collective course of action—for instance, whether to attack
another group—and differing opinions offer a prominent
role for leadership. Various specialized decision rules (ma-
jority rules, voting procedures, conformity, and minority
influence) might have emerged to support this aspect of
leadership.

Fourth, once a course of action is identified, it is
important to initiate group action. This is facilitated by
individual differences in temperament—assertiveness and
proactivity on the one hand, and patience, self-control, and
acquiescence on the other hand—which ensure that not
everyone is likely to make a first move (Ames & Flynn,
2007; Couzin et al., 2005; Nettle, 2006). A related problem
involves identifying individuals worth following because
they have the requisite competence and expertise. The
solution to this problem requires mechanisms for recogniz-
ing leadership potential, which humans possess in abun-
dance (Littlepage, Robinson, & Reddington, 1997; Lord,
Foti, & DeVader, 1984).

Finally, the problem of maintaining cohesion in
large, dispersed groups could be solved by specialized
mechanisms for communication, perspective taking, and
conflict management. Specific abilities such as theory of
mind, empathy, social identity, and language may have
played a role in maintaining group cohesion (de Waal,
1996; Haidt, 2006, 2007; Van Vugt & Schaller, 2008).
Also, the capacity for imitation and social learning along
with mechanisms that direct attention to higher status
individuals would prompt followers to emulate leaders,
thereby adding to group identification and cohesion
(Chance, 1967; Henrich & Gil-White, 2001). Punish-
ment of free riders (individuals who benefit from group
living without contributing to it) and rule enforcement
provide alternative means for maintaining cohesion and
are also crucial leadership functions (De Cremer & Van
Vugt, 2002).

Thus, specialized mechanisms for planning, commu-
nication, group decision making, competence recognition,
social learning, and conflict management would have con-
tributed to the emergence of a specific leadership and
followership psychology in humans. It remains to be seen
whether these evolved mechanisms were specifically de-

Robert
Hogan

184 April 2008 ● American Psychologist

signed to solve leadership problems or whether they were
co-opted for these purposes (cf. Buss, Haselton, Shackel-
ford, Bleske, & Wakefield, 1998).

Game Theory Analysis of Leadership
Game theory was devised during World War II to ana-
lyze strategic interactions among combatants; it has sub-
sequently become an important method for studying
social processes (Gintis, 2007). Evolutionary psycholo-
gists use game theory to model social behaviors such as
altruism, conformity, and social intelligence (Axelrod,
1984; Schmitt & Pilcher, 2004; D. S. Wilson, Near, &
Miller, 1996). Leadership and followership can also be
modeled, and framing them in terms of game theory does
three things. First it suggests the way leadership and
followership may have evolved. Second, it requires re-
searchers to consider the perspectives of leaders and
followers simultaneously, clarifying the costs and ben-
efits for each. Third, it suggests how individuals whose
interests potentially conflict might work together to
maximize mutual benefits.

Evolutionary game theory (Maynard-Smith, 1982)
views social interaction as a process in which strategies
compete in a Darwinian fashion. In these games, the agents
embody strategies that are encoded in genes and, over the
course of evolution, are tested against alternative strategies
and copies of themselves. Genes spread through a popula-
tion depending on the relative superiority of their associ-
ated strategies in evolutionarily relevant situations. By re-
garding leadership and followership as alternative game
strategies, we may be able to tell how well these strategies
fare in competition with each other as well as with alter-
native strategies.

The Leader Game

The game of leader (Van Vugt & Kurzban, 2007) can be
used to model the leader–follower coordination problem.
Table 1 depicts one version of this game, which can be
illustrated using an example from our ancestral environ-
ment. Note that although we use the simplest case—a
dyadic game—the analysis can be easily extended to a
coalition of actors or to multiple coalitions (Maynard-
Smith, 1982). Also note that the payoffs represent units of
reproductive success (the currency in evolution). Further,
the absolute value of these points matters less than the
ranking of preferences across the four game cells.

Suppose Pat and Jamie are both dehydrated and that
Waterholes A and B contain water. Whichever waterhole
they choose, they must travel together for protection. How-
ever, Pat prefers Waterhole A—perhaps because he or she
knows how to get there—and this advantage gives him or
her an outcome of �3. Jamie prefers Waterhole B—it is
closer to his or her family—and this advantage gives him or
her an outcome of �3. The payoffs are such that both Pat
and Jamie are better off going to the same waterhole, yet
this gives one of them a relative advantage (�2). The
asymmetrical payoffs in the leader game make it attractive
for players to take the lead. By coordinating on their
preferred hole, the leader gets a relatively better payoff
than the follower, which may ultimately be paid out in
greater reproductive success. Note that this game repre-
sents any social coordination problem—for example,
where to hunt, whether to fight or take a nap.

The coordinating cells (A, A or B, B; see Table 1) are
the equilibrium points of the game, an important concept in
game theory (Gintis, 2007). Natural selection will favor
adaptations that lead to equilibrium—where neither party
can obtain better payoffs by switching strategies—and this
is relevant to the emergence of leadership and followership
because leadership can lead to equilibrium. If people play
the game simultaneously, most pairs fail to coordinate
because each will opt for the leader role (Van Vugt &
Kurzban, 2007). However, if they play the game sequen-
tially and one person takes the lead by moving first or
indicating a preference (e.g., for Waterhole A), then most

Table 1
The Leader Game

Jamie

Pat

Waterhole A Waterhole B

Waterhole A 3, 1* 0, 0
Waterhole B 0, 0 1, 3*

Note. Payoffs are for Pat and Jamie, respectively; Waterhole A and Water-
hole B represent alternative game strategies (underpinned by gene alleles).
Game equilibria are indicated with asterisks.

Robert B.
Kaiser

185April 2008 ● American Psychologist

pairs coordinate.1 This analysis suggests that in species that
frequently encounter coordination problems, adaptations
for leadership and followership are likely to emerge. In
ancestral humans, these adaptations would have been sup-
ported by an increasingly sophisticated cognitive infra-
structure involving theory of mind, language, and culture,
with implications for the scale, complexity, and style of
leadership.

Note that this model makes no assumptions about the
design features of leadership and followership adaptations.
For instance, leader and follower roles may be adopted
flexibly by the same individual because in some cases it
pays to be a leader and in others to be a follower. This is
consistent with a conditional strategies model (West-Eber-
hard, 2003), which assumes that organisms adopt strategies
based on specific environmental and/or developmental in-
puts (see also Gangestad & Simpson, 2000, on strategic
pluralism)—for instance, being the firstborn in the family
or the tallest in the class might dispose people to assume
leadership roles in later life (Simonton, 1994). On the other
hand, natural selection may have coded leader and follower
strategies in a more static fashion, so that populations
reached equilibrium using strategies maintained through
frequency-dependent selection (Maynard-Smith, 1982;
D. S. Wilson et al., 1996). Such models suggest that pop-
ulations contain individuals with genotypes predisposing
them to either leadership or followership.2 As with sex
ratios, an increase in the frequency of leader genotypes in
a population reduces the payoffs for this strategy— because
many would-be leaders compete and fail to coordinate—
thus selecting against leader genotypes. The distinction
between conditional versus pure strategies is analogous to
the distinction between situational versus trait theories of
leadership (Van Vugt, 2006).

The Riddle of Following

An important implication of the leader game concerns the
origins of followership. Coordinated action serves the in-
terests of both leaders and followers, but the payoffs for
leaders are relatively better because they get benefits when
others adopt their goals (e.g., status and prestige; Buss,
2005; Henrich & Gil-White, 2001). Because natural selec-
tion is based on relative (rather than absolute) fitness, this
seems to make followership puzzling. Perhaps followers
simply make the best of a bad situation when they cannot
be leaders themselves (Dawkins, 1976). The mind may be
designed to evaluate one’s relative place in a hierarchy and
to evaluate the costs and benefits of competing for higher
status. Such a mechanism is implicit in the pecking order
phenomenon, first observed in chickens (Schjelderup-
Ebbe, 1935), which promotes stability over conflict in
hierarchical social groups. If the calculated costs of com-
peting for status outweigh the benefits, then followership
would be a rational choice that would free time and energy
for other pursuits (Gangestad & Simpson, 2000). Perhaps
to become leaders themselves someday, followers need to
defer to leaders to observe how they lead (Henrich &
Gil-White, 2001). Coordination benefits are also negotia-

ble, and followers can improve their relative benefits if they
engage in collective bargaining (Boehm, 1993, 1999).

There is a final intriguing possibility. Although the
payoffs for followers may be less than those for leaders,
coordination leads to higher aggregate-level payoffs (in
Table 1, an aggregate of �4 points vs. 0 points). Thus,
groups with an effective leader–follower structure would
have higher aggregate fitness. Under the right conditions
(discussed in Sober & Wilson, 1998; D. S. Wilson, Van
Vugt, & O’Gorman, 2008), leadership might create enough
variation between groups for natural selection to operate. It
is possible that well-led groups are so much better at group
hunting, food sharing, and warfare that the relatively lower
within-group payoffs for followers are compensated for by
between-groups fitness benefits. That is, followers may not
be as well off as their leaders, but they are better off than
individuals in poorly led groups.3 The interplay between
individual- and group-level selection pressures yields po-
tentially interesting implications for leadership. Multilevel
selection models have provided novel insights into such
social traits as culture and morality (Haidt, 2006, 2007;
D. S. Wilson et al., 2008).

A Natural History of Leadership
In this section, we present a hypothetical description of
how leadership practices evolved over the course of non-
human to human primate history. Such scenarios always
risk being just-so stories because their key assumptions are
difficult to verify. Nonetheless, clues embedded in the
relevant literatures can be used to estimate the time frame
and structure of social organizations that promoted changes
in leadership practices in human societies. We identify four
nominal stages (summarized in Table 2).

Stage 1: Prehuman Leadership

The phylogenetic evidence suggests that preadaptations for
leadership precede primates. Simple leader–follower struc-
tures for coordinating group movement have been observed
in various social species (Bloom, 2000; Boinski & Garber,
2000; Couzin et al., 2005; E. O. Wilson, 1975). For exam-
ple, the waggle dance of honeybees recruits other hive
members to visit food resources and can be construed as
leadership. The foraging patterns of many insects, the
swimming patterns of schools of fish, and the flying pat-
terns of migrating birds also resemble leader–follower re-

1 Yet, the greater the asymmetry in payoffs, the longer it takes to
establish coordination (Van Vugt & Kurzban, 2007).

2 Arvey and colleagues have conducted twin studies and estimate that
about a third of the variance in holding a professional leadership job is due
to genetic factors, which provides partial support for frequency-dependent
selection (Arvey, Rotundo, Johnson, Zhang, & McGue, 2006; Arvey,
Zhang, Avolio, & Kreuger, 2007).

3 Evolutionary models demonstrate that leadership substantially in-
creases variability in outcomes between groups (Richerson & Boyd,
2006). For instance, technological innovation, education, and quality of
life are far greater for citizens in modern democracies than for those in
dictatorships, totalitarian regimes, and corrupt societies (Bloom, 1997;
Diamond, 1997; rence & Nohria, 2002; Transparency International,
2005).

186 April 2008 ● American Psychologist

lationships. These examples suggest that species lacking
complex cognitive capacities can display follower behavior
using a decision rule as simple as “follow the one who
moves first.”

Group movement guided by leadership is also docu-
mented in nonhuman primates. Hamadryas baboons in
Ethiopia sleep in large groups on cliffs (Kummer, 1968).
They leave the cliffs in the morning to forage in open areas.
One individual, usually an adult male, will move a few
meters in a particular direction and sometimes the whole
group will follow. Sometimes, however, there are no fol-
lowers, and the would-be leader returns to the group. The
bidding starts again until the rest finally choose to follow
(Kummer, 1968). This reflects the two key decisions in the
leader game: the choice to initiate and the choice to follow.

Chimpanzees, our closest genetic relatives, often dis-
play peacekeeping, another response to a coordination
problem solved by leadership. The following incident from
the Arnhem Zoo chimpanzee colony was reported by de
Waal (1996):

A quarrel between Mama and Spin got out of hand and ended in
fighting and biting. Numerous apes rushed up to the two warring
females and joined in the fray. A huge knot of fighting, screaming
apes rolled around in the sand, until Luit [the alpha male] leapt in
and literally beat them apart. He did not choose sides in the
conflict . . . instead anyone who continued to act received a blow
from him. (p. 129)

De Waal (1996) argued that this peacekeeping behavior
constituted leadership because it was endorsed by the entire
group.

Leadership has also been observed during aggressive
encounters between groups of wild chimpanzees (Boehm,
1999; Wrangham & Peterson, 1996). Boehm (1999) re-
ported a conflict between neighboring chimpanzee groups
in Gombe, Tanzania, who met on a borderland in the forest.
The alpha male from one group charged the other group
and the rest followed him, prompting the other group to
retreat into its home range.

These examples support the claim that adaptations for
leadership and followership tend to evolve in social spe-
cies. This does not necessarily explain why leadership
evolved in humans; different selection pressures shaped the
adaptation of different species, and humans have many
unique adaptations (Buss, 2005; Darwin, 1871). Nonethe-
less, the continuity of evidence across species makes it at
least plausible that the selection pressures that gave rise to
leadership in nonhumans resemble those in humans.

Stage 2: Band and Tribal Leadership

It is likely that leadership was further shaped by the unique
evolutionary history of humans. One can think about modal
patterns of human leadership as evolving through three
stages. Each stage represents a change in the scale and
complexity of social organization and resource distribution
that had implications for the relationship between leaders
and followers.

The first (and by far the longest) phase extended from
the emergence of early humans around 2.5 million years
ago until the end of the last ice age, about 13,000 years ago
(Diamond, 1997; Wade, 2006). During this stage, the Pleis-
tocene era, humans lived in semi-nomadic hunter-gatherer
bands and clans consisting of 50 –150 mostly genetically
related individuals (Dunbar, 2004). Experts agree that mod-
ern hunter-gatherers—for example, the !Kung San of the
Kalahari Desert, the Yanomamo of the Amazon River
basin, the Inuit of the Arctic coasts, and the Aborigines in
Northern Australia—provide our best model for human
social organization in this stage, often referred to as the
environment of evolutionary adaptedness (EEA; …