|Quarterly Review of Biology, June 2002
v77 i2 p149(16)
Beyond dominance: the importance of leverage.
Rebecca J. Lewis.
Author's Abstract: COPYRIGHT 2002 University of Chicago
The dominance concept as it is currently defined and applied in
animal behavior is problematic. What has been traditionally
considered dominance is actually a combination of dominance in the
strict sense and power based upon other sources. Rather than working
within the current paradigm, I propose a conceptual revision founded
upon the more inclusive concept of power. Power is a phenomenon
where a dyadic relationship is asymmetrical (Simon 1953) and can be
divided into two types: dominance and leverage. Dominance is power
based upon the ability to use force. Leverage is power based upon a
resource that cannot be taken by force. Four characteristics of
power are used in sociology (base, means, amount, and scope) that
facilitate both the expansion of the power concept beyond
traditional dominance and the application of these theoretical ideas
in empirical studies. This cross-disciplinary approach to power
allows a wide range of behaviors to be considered as critical while
at the same time it focuses the attention of researchers to the
aspects of power that differ among dyads, classes, and species.
Power is not simply a linear combination of dominance and leverage,
and more research is needed before the exact nature of this
relationship can be clarified. By considering dominance as one form
of power, this framework fosters a more complete understanding of
power dynamics and their effects on animal societies.
power, dominance, leverage, relationships, biological markets,
resource holding potential, submissive signals
Full Text: COPYRIGHT 2002 University of Chicago Press
CONFUSION AND CONTROVERSY have surrounded the concept of
dominance almost since it was introduced by Thorleif
Schjelderup-Ebbe in 1922. Various authors (e.g., Bernstein 1981; de
Waal 1986; Hand 1986; Drews 1993; Piper 1997) have attempted to
clarify the dominance concept in hopes of creating consistency in
how it is applied, but the confusion persists. In particular,
interspecific comparisons have been complicated by the lack of a
single definition for dominance (cf. Drews 1993). This problem has
only been magnified with researchers using different methods for
applying the concept of dominance to empirical studies (e.g.,
direction of aggression: Vestergaard et al. 1993; priority of
access: Lemel and Wallin 1993; direction of aggression and priority
of access: Frank 1986; spatial position and priority of access:
Johnsson 1993; weight: Dugatkin and Ohlsen 1990). Consequently,
attempts to link dominance and fitness have met with mixed results,
causing the evolutionary significance of the dominance concept
itself to be called into question (for review: Fedigan 1983).
I propose a more inclusive framework for analyzing social
relationships based upon the concept of power. Power, as derived
from political science, economics, and sociology (where it has been
explicitly studied for decades), more accurately describes
asymmetries in relationships between individuals than the narrowly
defined traditional concept of dominance. Power is a phenomenon
where a dyadic relationship is asymmetrical (Simon 1953). The
asymmetry in the dyad may be related to resource holding potential
(RHP: Maynard Smith and Parker 1976; also called fighting ability:
Hand 1986; Noe 1990; Hamilton and McNutt 1997), but it can also be
based upon the fighting ability of coalition partners (de Waal
1996), the possession of an inalienable commodity (Noe et al. 1991),
an asymmetry of knowledge (Hand 1986), or even an asymmetry in
"dependence" (Emerson 1962). Simon's (1953) definition of power is
advantageous because it disconnects power from aggression. While
Simon is correct in asserting that A has power over B if an
asymmetry exists in this direction (regardless of whether A takes
advantage of it), some biologists contend that the asymmetry is only
of interest when preferences conflict (Hand 1986; Noe et al. 1991),
specifically in contest competition (Preuschoft and van Schaik
2000). Accordingly, Simon's definition of power will be used in this
paper with the assumption that asymmetries will only be expressed
when preferences conflict.
DOMINANCE AND LEVERAGE
Power is a more inclusive concept because it comprises both
dominance and leverage. In this framework, dominance is defined as
power based upon force or the threat of force (cf. "competitive
ability": de Waal 1989). This definition is consistent with much of
the previous research because dominance has traditionally been
associated with fighting ability (Packer and Pusey 1985; Chapais
1991; Pierotti et al. 1997). The close relationship between
dominance and fighting ability accounts for the fact that dominance
is often correlated with body size (Dugatkin and Ohlsen 1990; Lemel
and Wallin 1993; Piper 1997). Also note that dominance does not
require the use of force but can also be based upon the potential to
use force, for even the infrequent use of force can be very
effective (Chapais 1992). Following Hand (1986), two types of
dominance can be distinguished: (1) intrinsic dominance, based upon
an individual's own ability to use force; and (2) derived dominance,
based upon fighting ability that is not physically associated with
that individual, such as coalition and alliance partners. Thus,
bridging alliances, revolutionary alliances, and dependent rank are
all examples of derived dominance (Chapais 1992).
Power can also be based upon resources that cannot be taken by
force; that is, resource-based power or leverage (Hand 1986; Smuts
1987; Noe 1990; Noe et al. 1991; de Waal 1996). Leverage is thus
defined as power based upon inalienable resources, and can arise
from any number of asymmetries. Examples of resources that cannot be
taken by force, which form the basis for leverage, include
fertilizable eggs (Hand 1986), skills (Hand 1986), services (e.g.,
grooming: de Waal 1989), or even genes, as in kinship and inclusive
fitness (Hand 1986; de Waal 1996). An individual may have leverage
due to demographic variables, such as population sex ratios (Emlen
and Oring 1977), where "market effects" are likely to be observed
(Noe et al. 1991); indeed, mate choice (or the power to choose a
preferred mate) may be derived from these demographic variables (for
discussion of power and mate choice: Bergstrom and Real 2000). An
individual may also have leverage during acts of cooperation due to
the collective action problem (e.g., by the threat of free-riding:
Nunn and Lewis 2001), or by the threat of terminating the
collaborative effort (de Waal 1996)--for example, by being less
"dependent" upon the collaboration (power-dependency theory: Emerson
While a coalition partner, C, can conceivably be argued to be a
source of leverage for B in the dyad AandB, coalition partners in
the power framework are considered to be derived dominance
consistent with Hand (1986). For clarity, any source of power
relating to force is included with dominance. The coalition partner,
C, however, does have leverage in its relationship with B (dyad
BandC) because it is providing a service that B relies on in B's
relationship with A. For instance, in Chimpanzee Politics, de Waal
(1982) reports a series of takeovers in a colony of common
chimpanzees (Pan troglodytes). The situation involved three adult
males: Luit, Nikkie, and Yeroen. At one point Luit was the alpha
male, Nikkie was the beta male, and Yeroen had recently fallen to
the gamma position. Nikkie then formed a coalition with Yeroen to
overthrow Luit. Nikkie's takeover would not have been successful
without Yeroen's support, thus Nikkie had superior derived dominance
in his relationship with Luit due to his coalition with Yeroen
(Figure 1a). As a coalition partner, Yeroen provided additional
force for Nikkie and was therefore a source of dominance for Nikkie;
however, Nikkie needed Yeroen to maintain his position over Luit,
thus Yeroen had leverage in his relationship with Nikkie because of
Nikkie's dependence on the Nikkie-Yeroen coalition (Figure 1b).
Coalitionary support is not a resource or service that can be taken
by force, and thus was a source of leverage for Yeroen. In fact,
Yeroen did receive special benefits due to Nikkie's dependence on
him: Yeroen was able to mate approximately twice as often as Nikkie
in Nikkie's first year as alpha male, though when Nikkie was no
longer as dependent upon Yeroen to maintain his status, the
situation was reversed and Nikkie mated more than twice as often as
Examples of Leverage: Reinterpreting Data
Numerous examples may be found in previous research in which the
concept of power more precisely describes changes in dyadic
relationships that dominance alone was unable to explain. For
example, females in estrus often experience an advantageous change
in social relationships without changing positions in the dominance
hierarchy (Carpenter 1942; Hall and De Vore 1965; Datta 1983; de
Waal 1986). This change has puzzled researchers because it does not
fall in line with current theories about dominance. De Waal (1986)
attempted to alleviate this and similar problems by distinguishing
between two layers of dominance: formal dominance, which is stable,
and real dominance, which is flexible. While this distinction is
useful for identifying differences in power, recognizing layers of
dominance does not always clarify the dominance concept and leaves
vital questions unanswered. For instance, when is an observed
behavior formal dominance versus real dominance? What is the basis
for the difference? Are higher cognitive abilities required for
formal dominance (cf. Maestripieri 1996)? As de Waal (1986) stated
himself, adopting this new terminology is constructive but cannot
fully explain the phenomena.
By placing this observation of temporary changes in the status of
estrus females within the broader framework of power, the puzzle
disappears. As long as the female's ability to achieve outcomes
through force does not change, her dominance does not change.
Rather, the female rises to an advantageous position because her
leverage changes. She has an inalienable commodity: her egg that is
ready to be fertilized. When the female is no longer in estrus
(i.e., when that egg is no longer available), the female's leverage
decreases. Thus, temporary fluctuations in power are inevitable and
predictable. Signaling, which is used to differentiate between de
Waal's formal and real dominance, is shifted in this new framework
from defining dominance styles to a characteristic of power (see
below), where precise interindividual and interspecific comparisons
can be made. Moreover, complex cognitive abilities are not required
for leverage to occur (for debate about cognition and formal
dominance: Maestripieri 1996; Preuschoft 1999). Rather, individuals
only need to be able to perceive an asymmetry in the dyad.
The usefulness of the power concept is also evident in studies in
which cognition plays a role. For example, Stammbach (1988) trained
a long-tailed macaque (Macaca fascicularis) group to use a simple
lever machine to obtain food. The operation was then made more
complex and only a single subordinate individual was trained to
complete the task. Once the task was completed, however, other group
members were able to feed at the dispenser. Although the
knowledgeable subordinate did not rise in dominance rank, he
received significantly more grooming than before the training.
According to the traditional definitions of dominance, training the
subordinate did not increase his social power. With the broader
concept of power, however, the explanation is obvious: the
subordinate increased his leverage with his differential increase in
knowledge. A skill or knowledge can be a source of leverage (Hand
1986; Noe 1990) as long as it is a scarce commodity. This commodity
can be exchanged for other commodities or services, such as
Leverage can be viewed as economic power while dominance
is more physical in nature. These two types of power exist along a
continuum, but I will focus on the extreme forms for clarity (for a
discussion of leverage in terms of a cost to benefit ratio, "winning
inappropriately," see Hand 1986).
POWER AS A GENERAL TERM
The term "power" is not new to animal behavior, despite the fact
that dominance is used to explain most of the phenomena that relate
to power in animal societies. "Dominance" and "power" have even been
used interchangeably in the animal behavior literature (e.g., de
Waal 1982; Datta 1983, 1989; Chapais 1992). This historical
interchange of dominance and power comes from the fact that authors
have referred to dominance in different ways: dominance sensu
stricto, which is what I refer to as "dominance" in this framework,
and dominance sensu lato, which is what I refer to as "power."
Moreover, "power" is often used in the animal literature without the
author providing a definition (e.g., de Waal 1982, 1986; Datta 1983;
Smuts 1985; Noe 1992; Gowaty 1997; Vervaecke et al. 2000), yet when
power is defined, the definitions are neither consistent nor are
they always analogous to dominance. It is important for the two
terms "dominance" and "power" to remain distinct. According to the
framework introduced in this paper, power is the more general term
and may refer to either dominance or leverage (Figure 2). Moreover,
in this framework, power only refers to dyadic relationships (sensu
Hinde and Stevenson-Hinde 1976). Perhaps some polyadic "power"
phenomena do exist (Jessica Flack, personal communication), such as
"respect," "prestige" (Barkow 1975), or "referent power" (cf. Jones
2000). "Power" that goes beyond the dyadic level is probably rare
outside of humans, however. In addition, even polyadic "power" can
still be analyzed at the dyadic level with the framework provided,
assuming an asymmetry in this polyadic "power" exists in a dyad (see
also power-dependency and exchange networks: Cook and Emerson 1978;
Cook et al. 1983).
PROXIMATE CHARACTERISTICS OF POWER
Power has certain characteristics that can be used as a basis for
measure and comparison (see also Chapais 1991). Various social
scientists have put forth their own version of the list of important
qualities of power. Dahl (1957), however, provides a set of four
characteristics that seem most useful for the analysis of animal
behavior: base, means, amount, and scope. Base refers to the source
of power, such as fighting ability or control over mating
opportunities. Means refers to the instruments of power, such as a
threat or a reward, and is the way the relationship is negotiated.
Amount refers to the magnitude of power over a number of categories
(cf. "spheres of dominance": Hand 1986); in other words, amount
addresses the question of whether power varies with the context.
Scope is the range of power, and consists of B's responses to A
(i.e., the behaviors that A is able to evoke in B). Thus, base,
means, amount, and scope are ways to measure why, how, when, and to
what extent power occurs. These proximate characteristics allow
biologists to operationalize power, connecting the theoretical
construct to the day-to-day behaviors that researchers measure.
Moreover, these characteristics also permit researchers to move away
from simply using outcomes to define power.
For example, suppose that a male baboon has power over another
male baboon. His power is based upon his greater fighting ability
(i.e., dominance). He can enforce his power by means of a yawn, a
threat that demonstrates the size of his weapons (i.e., his
canines). The amount of his power over the other male could be an
85% probability of winning contested food and sleep sites, but only
a 55% probability of winning contests over receptive females. The
scope of his power includes the ability to evoke the entire
repertoire of submissive behaviors from the other male. At the same
time, this powerful male may experience a different relationship
with a female of his species. While the male has a greater fighting
ability than the female, she may have greater power based upon her
egg that is ready to be fertilized (i.e., leverage). She can enforce
this power by means of refusal to copulate with that male (i.e.,
withholding a reward). The amount of her power may indeed vary with
her reproductive state, and the scope of her power may include the
ability to elicit grooming and coalitionary support.
These proximate characteristics are critical to revising concepts
of power in nonhumans. The term "base" highlights why power occurs
and allows for nondominance powers to be considered as relevant.
"Means" implies more than just aggression; both agonistic and
affiliative behaviors may be used to negotiate power. "Amount" not
only addresses the issue of the context-dependency of power, but
because it is expressed as a probability, it also indicates how
often the power occurs. Finally, "scope" will often refer to (but is
not limited to) submissive behaviors: an individual may have the
power to evoke physiological responses such as musth suppression
(African elephants: Poole 1989). Scope can also include services
such as grooming, vigilance, or coalitionary support. These
characteristics facilitate the expansion of the concept of power
beyond traditional dominance in nonhumans, while at the same time
allowing for the application of these ideas in empirical studies.
CLARIFYING DOMINANCE WITH THE CONCEPT OF POWER
While various researchers have attempted to break free of the
narrow paradigm that power is limited to dominance (e.g., Noe et al.
1980; Hand 1986; Chapais 1991; Noe et al. 1991; Gowaty 1997), these
insights have yet to be incorporated into studies of social behavior
in animals. Dominance has been useful for explaining a good portion
of power relations in animal societies because it is a relatively
easy basis for an individual with greater fighting ability to
achieve its preferred outcomes. Nevertheless, other strategies for
achieving preferred outcomes are available. The concept of power
allows a wide range of behaviors to be considered as critical while
at the same time focusing the attention of researchers on the
aspects of behavior that differ among dyads, classes, and species.
This broader concept of power reduces the confusion historically
associated with traditional dominance.
First, the definition of dominance is simplified within the
framework of power. Dominance refers to a phenomenon where an
individual's preferences take precedence in a dyadic relationship
because of an asymmetry in fighting ability. The ability to use
force can be gauged with measures such as body size, weapon size,
and number and strength of coalition partners. Only when the power
dynamic is based upon force or the threat of force can it be called
dominance. If the power base is uncertain, the more general term
"power" is preferable.
Second, this clear definition of dominance delineates
clear applications. Dominance, like all forms of power, is dyadic.
Sometimes "male dominance" or "female dominance" is used to refer to
the power of one class of individuals relative to another class of
individuals. These terms are useful as shorthand for a general
phenomenon as long as the measures and implications remain dyadic.
Female dominance, in particular, has stirred a heated debate in the
primate literature. Some primatologists follow a classic ethological
approach by defining dominance in terms of the outcomes of agonistic
encounters (e.g., Pereira et al. 1990). Others (e.g., Jolly 1984)
contend that female dominance is essentially different from male
dominance because it concerns priority of access to resources.
Within the framework of power, however, female dominance over males
occurs only when female fighting ability is superior to males in
intersexual dyadic interactions. Species in which males and females
have equal abilities to use force may exhibit female priority of
access to resources based upon economic power; these species exhibit
female leverage, not female dominance. Moreover, when power
structures are not sex dependent, such as in the monomorphic brown
hyena, Hyaena brunnea (Owens and Owens 1996), shorthand terms such
as female dominance are not constructive and should be avoided.
These cases demonstrate that the dyadic analysis of power dynamics
has more utility than analysis of sex classes.
Finally, nonaggressive behaviors that may influence power
relations are often ignored within the traditional dominance
framework (Hand 1986). By defining dominance in terms of the ability
to use force, the connection between power and aggressiveness is
severed. This disconnection will allow for more accurate
descriptions of power structures. Aggression and power may be
associated because aggression is one manifestation of power (cf.
means) but not because aggression levels determine power (Francis
The concept of power improves upon the traditional concept of
dominance by placing it in a more complete framework. Leverage has
been a missing component. Not only is power more inclusive than
dominance, but it can also be broken down into four aspects that can
be used to more accurately understand the nature of dyadic
Some zoologists have argued that traditional dominance is
context-dependent (e.g., Popp and De Vore 1979; Hand 1986; Francis
1988; Verbeek et al. 1999), while others have claimed that in order
for dominance to be a useful concept it must be independent of
context (e.g., Bernstein 1981). An individual's power may vary in
the dyad, however, due to age, hormonal status, or even population
demographics. In many cases, leverage may be context specific while
dominance is independent of context and may be relatively constant.
Amount (sensu Dahl 1957) is a characteristic of power that can be
used to ascertain context dependency. The amount of power that an
individual has in a relationship can be determined by calculating
the probability of "winning" a contest in different situations. This
information can be further subdivided into the amount of dominance
and amount of leverage (i.e., with different bases), or into the
amount of power needed to evoke different submissive signals,
physiological responses, or mating opportunities (i.e., scope).
The framework presented here is also useful for analyzing
"site-dependent dominance," a term common in, but not limited to,
the avian literature (for review: Oberski and Wilson 1991; Piper
1997). What has been traditionally called "site-dependent dominance"
refers to the ability of some individuals to win more conflicts in
areas that ate familiar to them. For example, J L Brown (1963) found
that a Stellar's jay (Cyanocitta stelleri) wins encounters when it
forages in its nesting area but that social status declines with
distance from that nesting area. In other words, a bird has a
greater amount of power within its territory but as it moves away
from its territory, its power is gradually reduced. Because the
ability to use force is not likely to change with the location of
the dyad, in most cases dominance probably remains constant across
different sites. Knowledge of the area is one variable that does
change with location, however, and knowledge can be a source of
leverage (Hand 1986). Accordingly, some cases of "site-dependent
dominance' may be more appropriately labeled "site-dependent
leverage"; for example, if the relationship is based upon knowledge
and this leverage varies in amount depending on the location of the
dyad (see also the less extreme form of leverage, "winning
inappropriately": Hand 1986). As discussed above, by measuring both
the amount of power (context) and the base of power (source),
investigators can more precisely examine and compare the nature of
dyadic relationships when they ate evaluated within the framework
presented here. It is also important to note that by definition
power terms such as "site-dependent dominance" and "site-dependent
leverage" refer to relationships and not to interactions (see
Variation in power may influence fitness because it is ultimately
related to access to resources. By only examining the relationship
of dominance to reproductive success (e.g., Dewsbury 1981; Huck et
al. 1988; de Ruiter and van Hooff 1993; Inoue et al. 1993; Schartl
et al. 1993; Lambert et al. 1994; Holekamp et al. 1997; Pusey et al.
1997; Bartos and Perner 1998; Takahata et al. 1999; van Noordwijk
and van Schaik 1999), a study may be incomplete. The influence of
rank on reproductive success is more complex than predicted by
aggression-based models (Berard 1999). The variable results of these
studies may be the consequence of too narrow a definition of the
powerful individual. Power structures are more than just dominance
hierarchies and should be examined as such.
It is important to keep in mind that dominance and leverage
themselves cannot evolve (Rowell 1974; Bernstein 1981). Both
dominance and leverage refer to a relationship (e.g., Bernstein
1981; Hand 1986; van Hooff and Wensing 1987; Dewsbury 1990; Drews
1993) rather than an individual (e.g., Maslow 1940), and natural
selection cannot act directly on a relationship. Natural selection
can, however, act upon the tools that may improve an individual's
position in a relationship (e.g., body size or intelligence:
Another important aspect of power that is often confused in
cross-species comparisons is that asymmetries may differ between
dyads composed of strangers and dyads in which an established
relationship exists (Lemel and Wallin 1993; Preuschoft and van
Schaik 2000). When two individuals have never met before or both
individuals do not recognize each other, a relationship does not
exist (cf. Hinde and Stevenson-Hinde 1976) and the terms "power,"
"dominance," and "leverage" are not appropriate (see also Hand
1986). Power arises out of a dyadic relationship (cf. Simon 1953).
Interactions between strangers may be influenced by asymmetries;
these interactions should be referred to by other terms that
indicate the basis of the asymmetry, however (e.g., size,
experience, fighting ability). Strangers are likely to use signals
to assess these asymmetries (Lemel and Wallin 1993; Preuschoft and
van Schaik 2000) because they do not have an established
Only when two individuals recognize that they have had repeated
interactions with one another can a relationship arise (Hinde and
Stevenson-Hinde 1976). Power becomes an important factor in the way
two individuals with established relationships interact.
Distinguishing between dyads of familiars and strangers may
therefore be critically important (Preuschoft and van Schaik 2000).
Individuals with established relationships may also use signals
to communicate asymmetries. Primatologists have noted that some
primates, such as macaques and chimpanzees, exchange signals between
dominants and subordinates. These formalized status signals are
unidirectional and consistent across context and time (de Waal
1986). As mentioned above, de Waal (1986) created a double-tier
hierarchy within the traditional concept of dominance based upon the
observation that these formalized status signals do not always agree
with priority of access to resources. He suggested that formal
dominance is stable and is evident in the unidirectionality of the
formal dominance signals. These signals, he asserted, act as a
confirmation of the established social relationship. Real dominance
does not involve these formal exchanges and permits flexibility
across time and context. De Waal recognized how constricted and
problematic the traditional dominance definition was and attempted
to alleviate these problems. By working within the dominance
paradigm, he highlighted the differences between types of power and
helped pave the way for the framework presented in this paper.
Power includes both de Waal's (1986) formal and real dominance.
His two types of dominance refer to scope (sensu Dahl 1957). An
individual that has the power to evoke formalized status signals has
a different scope of power than an individual that never receives a
formal signal. Moreover, de Waal's real dominance is a combination
of leverage and derived dominance (although some derived dominance
can reach the level of de Waal's formal dominance).
The issue of relationships is also important when considering
power and motivation (defined here as an asymmetry in need). Hunger
and other physiological states have been shown to influence the
outcomes of animal contests (musth in African elephants: Poole 1989;
hunger in great tits: Lemel and Wallin 1993). Not all physiological
states are sources of power, however. Hunger is not a desirable
resource even though it cannot be taken by force. Estrus, on the
other hand, can be a source of power because the female has
something that a male wants: a fertilizable egg is a desirable
resource for males. Physiological states such as hunger determine
the willingness of an individual to escalate the conflict, and thus
do have an impact on a particular interaction. In fact, together
dominance, leverage, and motivation determine the outcome of
competition (cf. de Waal 1989). Nevertheless, while this type of
motivation can influence the outcome of a conflict, it does not
influence the dyadic relationship per se.
For instance, imagine two male spotted hyenas arriving at a small
carcass at approximately the same time. Hyena A has superior
fighting ability to hyena B, and thus A ultimately has the power to
keep B away from the carcass. Further suppose, however, that hyena A
has eaten recently and that hyena B is much hungrier. In this
instance, hyena A still wants the newly found food, but it prefers
to avoid a major contest and find another food source later. Hyena
B, on the other hand, would prefer to fight for the carcass rather
than hunt for food elsewhere, and is thus more willing to escalate
the contest. The key difference between the behavior of the two
hyenas lies more in the persistence and escalation of the hungry
hyena than in the bases of power which determine their long-term
dyadic relationship. This example illustrates the point that a
contest is only interesting in terms of power dynamics if animals
truly have conflicting preferences. While both hyenas would eat the
food if it were uncontested, they do not actually have conflicting
preferences because one is motivated by intense hunger and the other
is not (for discussion of motivation and conflicting priorities in
conflicts: Hand 1986). Motivation, as described above, may influence
the outcomes of occasional encounters, but it does not influence
relationships. Amount (sensu Dahl 1957) is the characteristic of
power that measures the probability of winning a contested resource.
Over time, any transient motivational differences ate unlikely to
change the relative amount of power in a relationship. Motivational
asymmetries can be used to influence relationships when motivation
is explicitly related to dependency on exchange (see
power-dependence theory: Emerson 1962). When an animal controlling a
resource that is needed by another exploits that need in order to
gain access to some other resource, then the asymmetry in need acts
as a source of leverage. For example, suppose that a male lion has
superior fighting ability and can keep another hungrier male lion
away from a carcass, but the dominant male perhaps needs some
assistance in taking over a pride of female lions. If the dominant
male uses the hungry lion's greater need for food as a basis of
exchange, then the exchange constitutes more than a simple
interaction. While the relationship may have started as a result of
an asymmetry during ah interaction, the system of exchange that was
established influences the dyadic relationship: one lion needs food,
the other lion needs assistance, and the exchange may continue until
the needs of both are satisfied. Thus, motivation can only be used
as a source of leverage if the dependency is linked with exchange
(i.e., it is used as economic power).
While power is often easy to recognize, operationalizing power is
not as simple. The use of different methods for measuring power has
exacerbated the problem of multiple definitions. While definitions
such as priority of access to resources demonstrate that a power
relationship exists, they do not provide any information on why that
power relationship exists. The definition of power as an
asymmetrical dyadic relationship is sufficient; power must be
measured and analyzed by its characteristics.
APPLICATION: POWER MATRICES
Much of the previous research on dominance is directly
transferable into the power framework. Past studies of dominance
have actually tested certain aspects of power. For instance, any
research that has studied priority of access to food (e.g., Terrill
1987) or water (e.g., Roeder and Fornasieri 1995) has demonstrated
which individuals have power in the feeding context. Amount of power
can be further elucidated by determining the probability of getting
a preferred food item. Hierarchies that are based upon the priority
of access to food can then be compared with hierarchies based upon
the priority of access to other resources, such as females, nests,
of burrows. In addition to determining amount of power, the matrix
method can also be used to examine the means of power, such as
aggressive behaviors (e.g., spotted hyenas: Jenks et al. 1995), and
the scope of power, such as submissive behaviors (e.g., wolves: van
Hooff and Wensing 1987) or retreats (dark-eyed juncos: Yasukawa and
The key difference between previous studies of dominance and the
power framework presented here is that the limitations of these
individual matrices are acknowledged. No one matrix or hierarchy
portrays the complete picture; a combination of matrices provides a
skeletal descript on of the total power structure, however, allowing
researchers to determine what behaviors in which contexts have a
certain probability of evoking specific responses in other
individuals. The researcher must delve deeper to determine the base
of power. Estimates of the relative abilities to use force are
needed, including body size, body condition, and number of coalition
For example, Vervaecke et al. (1999) conducted experiments to
evaluate the consistency of competitive abilities and (traditional)
dominance in captive bonobos (Pan paniscus). They assigned
(traditional) dominance ranks based on asymmetrical submissive
behaviors in dyads. The age and weight data that they provide can be
used to roughly estimate relative fighting abilities, and hence,
intrinsic dominance. The differences between their dyadic and
triadic tests can then be used to estimate extrinsic dominance,
creating a fairly complete picture of the dominance structure of
this group of bonobos (Table 1).
Vervaecke and colleagues (1999) present a matrix of frequencies
of fleeing and peering (submissive behaviors) during competitive
feeding bouts (Table 1) that can be used to measure scope (responses
that can be evoked). Because this matrix only contains data obtained
when animals give or receive aggressive behavior, the matrix can
also be used to examine one means of power (i.e., the effectiveness
of aggression as an instrument of power). In addition, this very
same matrix presents the data in terms of frequencies. Therefore,
the amount of power can also be analyzed. The amount of power refers
to the percentage of time that an individual "wins" a conflict in a
particular context, in this case, feeding.
Thus, for example, Dzeeta has 100% probability of evoking peering
and fleeing (scope) from Desmond with aggression (means) in the
feeding context (amount); Dzeeta is twice as likely to receive a
flee than a peer in this situation, however (amount and scope). In
contrast, Dzeeta was never seen to receive a flee from Kidogo in the
same context, despite evoking five times as much submissive behavior
from Kidogo. Hence, Dzeeta has a greater scope of power with Desmond
than with Kidogo when she uses aggression in the feeding context.
The base of Dzeeta's power is difficult to resolve from the
information provided in the article, though Vervaecke and colleagues
do present some clues. First, Dzeeta was 22 years old and weighed 50
kg at the time of the study, while Desmond and Kidogo were recorded
to be 23 years and 58 kg and 10 years and 42 kg, respectively. This
information suggests that, while it may have been a basis for
Dzeeta's power with Kidogo (see also Vervaecke et al. 2000),
dominance does not fully explain Dzeeta's relationship with Desmond.
Second, Dzeeta is a female while Desmond and Kidogo are males. The
potential leverage effects based upon Dzeeta's reproductive state
are unclear because the authors of the study spread the tests over
different phases of the females' sexual swelling cycles.
Nevertheless, the data presented imply that leverage could have
played an important role in the relationship between Dzeeta and
The above example based upon the work of Vervaecke et al. (1999)
demonstrates the utility of the power framework. It embraces the
problem that matrices based upon different behaviors produce
different hierarchies (see van Hooff and Wensing 1987). It also
allows researchers to go beyond general statements concerning the
power of one individual relative to another; the components of that
power can be identified and singled out for further analysis.
Additionally, power structures can be more accurately described and
compared across dyads, classes, groups, and species.
The utility of applying the framework of power is also
exemplified with the research of Thompson (1960a,b), who conducted
behavioral observations on wild and captive house finches
(Carpodacus mexicanus). Table 2 is a matrix from this study and is
based upon the ability to make an opponent retreat. Interactions
that caused the subordinate individuals to retreat (scope) were
called "hostile encounters" by Thompson (1960b), and thus the means
of power can potentially be interpreted as aggression. Unlike the
bonobo study, this matrix is not limited to the feeding context.
Female RB has an 11% probability of evoking a retreat (scope) from
male R with aggression (means), but 100% probability of evoking a
retreat from male WW with aggression. In other words, RB is not as
successful as the bonobo Dzeeta (discussed in the previous example)
at using aggression to evoke certain types of submission in males.
Of course, the data used to determine Dzeeta's power was limited to
the feeding context, and she may not have the same amount of power
outside of this.
The finch study also illustrates the utility of breaking down
power into its different bases. Female RB had only one leg when she
was captured, and while she had the power to make other birds
retreat at the beginning of the study (the matrix presented in Table
2 represents this time period), she quickly tired and was at a
disadvantage when encounters required force (Thompson 1960b). This
asymmetry in fighting ability became apparent and the scope of her
power gradually diminished. Her weight may have been greater at the
beginning of the study, but several months after the initial
hierarchy (presented in Table 2) was developed, she had dropped to
the lowest rank in the hierarchy and was the lowest in weight.
Without the data on initial weights, the base of RB's power cannot
be conclusively established. Hence, collecting body weight and
condition data throughout the entire study is crucial to truly
understanding the power dynamics of a dyad.
Nonetheless, Thompson (1960a,b) found that power in
intersexual dyads varied across the year (Figure 3). A hierarchy
based on agonistic encounters will vary in this species depending
upon which months the finches were observed. Females are more
powerful when they are without young and being courted, but in the
spring and early summer, when they form pairs and rear their young,
the males become more powerful (cf. Thompson 1960a,b). If male and
female fighting abilities vary seasonally, then males can be said to
become dominant during this brief period. A more likely explanation,
however, is that a different asymmetry in the dyad changes: females
rely on males to help feed them during the period of incubation and
to help feed the young after they hatch (Thompson 1960a). When males
depend upon females for mating opportunities, females have leverage.
Once females can no longer offer mating opportunities and depend
upon male services, males have leverage (see also gibbons: Reichard
1995:89). Thus, weight may not be the best determinant of power in
intersexual dyads in this species.
The bonobos in the Vervaecke et al. (1999) experiments were
studied in pair tests where service economies, and hence leverage,
may not always become apparent. Nevertheless, leverage, possibly
based upon sexual status of the female, may have played an important
role in this study. Leverage also probably explains the variation in
male-female relationships in the finch study. Unfortunately, the
data that ate most lacking from previous studies are descriptions of
the social economy in order to examine leverage. This gap leaves
important questions unanswered. For example, is the sex ratio in the
neighborhood (all individuals/groups that have "repeated
acquaintance": cf. Jolly 1966:148; Richard 1978:166) male-biased of
female-biased? The supply and demand of males and females may
influence power relationships (cf. Noe et al. 1991). What ate the
reproductive states of all relevant individuals? Do certain
individuals have special skills or resources that can be exchanged
or interchanged? Hemelrijk's (1990) interchange matrices may help
isolate relationships affected by leverage.
One note of caution is necessary, however. Researchers must be
careful in assessing what behaviors of resources ate being exchanged
during interchange. For example, Hemelrijk and colleagues (1992)
found that male chimpanzees more often groomed estrous females with
whom they mated more frequently; thus they suggested that this
result may reflect a sexual exchange between males and estrous
females. In a later paper (Hemelrijk et al. 1999), however, they
found that the male chimpanzees who groomed estrous females with
whom they had mated more often did not sire more offspring with
those females; thus they then suggested that trade did not occur.
While paternity is the ultimate goal of a male trading with an
estrous female, it is not necessarily what the female offers for
exchange. Female chimpanzees can only offer mating opportunities to
males. They can influence the likelihood of paternity with the
timing of this exchange, but they cannot, to my knowledge, control
the paternity of their offspring unless they only mate with one
male. Females can only trade those resources over which they have
control, which in this case is mating opportunities.
Researchers have already been measuring much of the
pertinent information to analyze power. The problem with the
traditional dominance concept has not been the existence of
competing methods for measuring and analyzing dominance. Rather,
most of the difficulties associated with the traditional dominance
concept are the result of a theoretical framework too narrow to
encompass all aspects of power.
RELATIONSHIP BETWEEN DOMINANCE AND LEVERAGE
The above examples highlight the fact that the relationship of
dominance and leverage is unclear. It would be useful if power were
a linear combination of dominance and leverage. Unfortunately, the
exact nature of the relationship is difficult to determine without
more empirical observations. At a basic level, power (P) can be
thought of as a function of dominance (D) and leverage (L),
P = f(D,L)
where power refers to the ability of A to make B do something
based upon an asymmetry, and dominance and leverage refer to the
basis for this power. The following descriptions of the above
function are assumed to be true:
As dominance increases, power increases ([DELTA]P/[DELTA]D
[greater than or equal to] 0).
As leverage increases, power increases ([DELTA]P/[DELTA]L
[greater than or equal to] 0).
The more dominance an individual has, the less additional power
an individual gains by adding more dominance
([[DELTA].sup.2]P/[DELTA][D.sup.2] < 0). The more leverage an
individual has, the less additional power an individual gains by
adding more leverage ([[DELTA].sup.2]P/[DELTA][L.sup.2] < 0).
The effect of leverage on power may depend upon how much
dominance an individual may have and vice versa
([[DELTA].sup.2]P/[DELTA]D[DELTA]L = ???).
Additional research is needed to determine how dominance and
leverage interact. I suspect that extreme dominance negates leverage
at any level. In a species that is highly sexually dimorphic in body
size, the smaller sex has very few options for leverage: most
resources can be taken by force by the larger sex. For example,
northern elephant seal (Mirounga angustirostris) sex ratios at
rookeries range from 20-100:1 to 1:3 across the mating season (Le
Boeuf and Reiter 1988). Despite the variation in sex ratios, the
females probably do not enjoy an increase in leverage in intersexual
dyads because of sexual dimorphism (males are 3-4 times heavier and
1.4 times longer than females; Deutsch et al. 1994). Perhaps the
only sources of leverage in these types of species are skill and
knowledge. Nevertheless, force can still be used to coerce a
smaller, knowledgeable individual into giving up that information
(e.g., torture in humans). Hence, leverage may simply not be
relevant in this case. When dominance is not so extreme, the
interaction between leverage and dominance is not as clear. For
instance, female Western gulls (Larus occidentalis) are 20-25%
smaller than males and yet have essentially egalitarian intersexual
relationships (Pierotti et al. 1997). Leverage is likely to play a
role in these relationships. More research is clearly needed to
elucidate the relationship between dominance and leverage.
The dominance concept as it is currently defined has
deficiencies. As a result, a body of literature has developed that
is confusing and contradictory. The "tight logical theory" that
Bernstein (1976) professed to exist has been repeatedly called into
question. Hand (1986), Noe et al. (1980, 1991), Noe and Hammerstein
(1994, 1995), and others have made significant advancements in the
study of power in animal behavior. No previous study has recognized
that leverage and dominance are fundamentally different, however.
Rather than modifying the dominance concept within the current
framework, dominance is more appropriately considered within the
greater context of power. When this approach is taken, much of the
present confusion associated with dominance is resolved.
Furthermore, the broader framework of power embraces many other
currently accepted ideas about social relations, creating the
possibility for more integrated theories. Many researchers have
demonstrated the existence of leverage without necessarily
expressing it as their intention. Thus, while additional research is
needed that explicitly tests for the effects of leverage, the
crucial issue to address now is how dominance and leverage interact
to create the overall power dynamic within a dyad.
Total frequencies of fleeing upon aression and peering in the dyadic
Actor Dzeeta Hermien Desmond Kidogo Hortense Ludwig
Dzeeta -- 0 0 0 0 0
Hermien 2 (2,0) -- 0 0 0 0
Desmond 3 (1,2) 2 (2,0) -- 0 0 0
Kidogo 15 (15,0) 10 (5,5) 1 (1,0) -- 0 0
Hortense 2 (1,1) 4 (4,0) 9 (9,0) 3 (3,0) -- 0
Ludwig 37 (36,1) 1 (1,0) 1 (1,0) 1 (0,1) 4 (3,1) --
Individuals in order of their dyadic competitive feeding rank. Actors
are the individuals fleeing or peering, while receivers are the other
individuals in the dyad. Sum of peering and fleeing upon an aggression.
In parentheses: first frequency of peering, then frequency of fleeing
upon an aggression. The above table is from Vervaecke et al. (1999).
Frequencies of wins in mixed groups of caged male and female
house finches from November 14 to December 17, 1954
Winners Sex RB WB [R.sub.F] WR [R.sub.M] W WW BB B
RB F -- 7 14 12 2 1 9 6 6
WB F -- 19 39 20 0 34 23 34
[R.sub.F] F -- 28 28 23 23 21 18
WR F 1 -- 42 2 47 1 39
[R.sub.M] M 16 1 1 1 -- 24 62 26 62
W M 29 20 -- 21 15 16
WW M 1 2 -- 26 60
BB M 1 2 33 1 1 2 -- 60
B M 1 6 --
F = female; M = male. A "win" is defined by the ability to make
an opponent retreat in a hostile encounter. The above table is
taken from Thompson (1960b).
I would especially like to thank C van Schaik for our numerous
discussions that helped me to clarify my thoughts about power and
for his unlimited enthusiasm and encouragement. E C Kirk provided
invaluable emotional and logistical support as well as helpful
comments on the manuscript. I am also grateful to D Brockman, K
Dausmann, L Digby, K Glander, M Munger, C Nunn, D Overdorff, and K
Smith for their discussions on this topic as well as comments on the
manuscript. This research also benefited from comments at an
informal talk given at the department of Biological Anthropology and
Anatomy at Duke University, from discussions with Signe Preuschoft,
Jessica Flack, and Frans de Waal, and from comments by two anonymous
reviewers. This research was supported by a NSF Graduate Student
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REBECCA J. LEWIS
Biological Anthropology and Anatomy, Duke University Durham,
North Carolina 27708 USA