The evolution of rape: The fitness benefits and costs of a forced-sex mating strategy in an evolutionary context

Article (PDF Available)inAggression and Violent Behavior 18(5):484–490 · September 2013with343 Reads
DOI: 10.1016/j.avb.2013.06.006
Past theorizing on the evolution of rape adduced the hypothesis that this act constitutes the behavioral expression of a mechanism which has evolved to enable men of low mate value to circumvent female choice. This has recently been questioned on the grounds that during human evolution, women's mate choices were controlled by their parents. It, therefore, remains unclear which were the evolutionary forces likely to have shaped this mechanism and whether such a mechanism exists in the first place. Accordingly, this paper employs anthropological and historical evidence in an attempt to reconstruct the evolutionary context in which a forced-sex mating strategy emerged. On the basis of this evidence, it is argued that forced sex is the outcome of an innate conditional strategy which enables men to circumvent parental and female choice when they experience a competitive disadvantage, or when the costs of doing so are low. The implications of the operation of this mechanism during human evolution are further explored.

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Available from: Menelaos Apostolou, May 01, 2014
The evolution of rape: The tness benets and costs of a forced-sex
mating strategy in an evolutionary context
Menelaos Apostolou
University of Nicosia, 46 Makedonitissas Ave., 1700 Nicosia, Cyprus
abstractarticle info
Article history:
Received 15 November 2012
Received in revised form 27 June 2013
Accepted 27 June 2013
Available online xxxx
Forced-sex mating strategy
Parental choice
Female choice
Anti-rape mechanisms
Past theorizing on the evolution of rape adduced the hypothesis that this act constitutes the behavioral ex-
pression of a mechanism which has evolved to enable men of low mate value to circumvent female choice.
This has recently been questioned on the grounds that during human evolution, women's mate choices
were controlled by their parents. It, therefore, remains unclear which were the evolutionary forces likely to
have shaped this mechanism and whether such a mechanism exists in the rst place. Accordingly, this
paper employs anthropological and historical evidence in an attempt to reconstruct the evolutionary context
in which a forced-sex mating strategy emerged. On the basis of this evidence, it is argued that forced sex is
the outcome of an innate conditional strategy which enables men to circumvent parental and female choice
when they experience a competitive disadvantage, or when the costs of doing so are low. The implications of
the operation of this mechanism during human evolution are further explored.
© 2013 Elsevier Ltd. All rights reserved.
1. Introduction ............................................................... 0
2. The evolutionary context of rape ..................................................... 0
3. The evolution of rape ........................................................... 0
3.1. Circumventing parental choice ................................................... 0
3.2. Circumventing female choice .................................................... 0
3.3. Opportunistic sexual access .................................................... 0
4. Parental anti-rape mechanisms ...................................................... 0
5. Forced-sex mating strategy across cultures................................................. 0
5.1. Forced-sex mating strategy in agropastoral and in hunting and gathering societies ........................... 0
5.2. Forced-sex mating strategy in post-industrial societies ........................................ 0
6. General discussion ............................................................ 0
References .................................................................. 0
1. Introduction
Certain men under certain conditions pursue a forced-sex mating
strategy (i.e., rape). This raises the question of the evolutionary ori-
gins of this behavior. Two main hypotheses have been proposed.
First, this strategy is the byproduct of other adaptations such as a
high libido, desire for novelty in sexual partners, and willingness to
engage in casual sex (Thornhill & Palmer, 2000). Second, rape is an
adaptation that has evolved to enable men to increase their reproduc-
tive success (Thornhill & Palmer, 2000).
In the latter hypothesis, the asymmetry in parental investment,
with females investing more in their offspring than males, turns the
former into the scarce reproductive resource over which the latter
strive to gain sexual access (Trivers, 1972). This puts women in a po-
sition where they are able to exercise choice. Women do not choose
randomly, but instead prefer men with characteristics such as good
genes, high social status, and control of resources which are benecial
for them (Buss, 2003).
These female preferences mean that men who lack desirable qual-
ities are unlikely to be chosen as mates, suffering in effect consider-
able reproductive costs. Given that men vary in their qualities, at
every point in time there should be several men who nd themselves
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Please cite this article as: Apostolou, M., The evolution of rape: The tness benets and costs of a forced-sex mating strategy in an evolutionary
context, Aggression and Violent Behavior (2013),
in the unfavorable position of lacking what women want. According-
ly, a forced-sex mating strategy is likely to constitute a behavioral
adaptation that enables men of low mate value to circumvent female
choice, and, in effect, resolves the problem of sexual access (Thornhill
& Palmer, 2000).
This hypothesis has recently been questioned on the grounds that
during human evolution female choice was a weak selection force be-
cause women's mate choices were controlled by their parents
(Apostolou, 2012b). It has been argued instead that if a forced-sex
mating strategy constitutes indeed a behavioral adaptation, it primar-
ily evolved to circumvent parental choice. It therefore remains
unclear which evolutionary forces have shaped such a mechanism.
Failure to describe these forces, and thus the presence (or absence)
of recurrent benets associated with this strategy, also makes it
unclear whether rape is the expression of a behavioral adaptation or
a byproduct of other behavioral adaptations. The purpose of this
paper is to identify these evolutionary forces and develop a compre-
hensive evolutionary framework that will account for the phenome-
non of rape.
2. The evolutionary context of rape
An evolutionary framework needs to be applied if the ultimate
causes of a behavioral mechanism are to be identied. The application
of evolutionary reasoning in understanding human behavior is based
on the assumption that the human mind has been shaped predomi-
nantly by evolutionary forces operating in an ancestral environment
which is different from that found in Western societies (Tooby &
Cosmides, 1990). Therefore, by employing anthropological and his-
torical evidence on pre-industrial societies, we can identify the evolu-
tionary pressures which are likely to have shaped a forced-sex mating
Parents and children have conicting interests over mating that is,
the mate choices of the former do not serve the best interest of the latter
(Apostolou, 2008b; Buunk, Park, & Dubbs, 2008; Trivers, 1974). This
gives the incentive to parents to place the mating decisions of their
children under their control and choose as spouses for them those indi-
viduals who best serve their interests (Apostolou, 2010b). Moreover,
owing to asymmetry in parental investment, with women being the
scarce reproductive resource to which men strive to gain access,parents
are more interested in controlling the mate choices of their daughters
than of their sons (Perilloux, Fleischman, & Buss, 2008).
In the majority of pre-industrial societies, parents are successful in
doing this. That is, in societies in which subsistence is based on hunt-
ing and gathering the most common mode of long-term mating is ar-
ranged marriage (Apostolou, 2007). This is also the case in societies
where subsistence is based on agriculture and animal husbandry,
and in both society types, daughters are controlled more than sons
(Apostolou, 2010b).
This evidence indicates that strong parental control over mating
has been prevalent during most of human evolution. In particular,
the genus Homo appeared on earth approximately 2 million years
ago and until about 10,000 years ago all humans were living as
hunters and gatherers (Lee & Devore, 1968). The way of life of these
ancestral foragers probably resembled that of their modern counter-
parts (Lee & Devore, 1968). Accordingly, the patterns of mating
found among modern foragers such as arranged marriage are likely
to have been prevalent among ancestral ones, a hypothesis that is
supported also by research based on phylogenetic analysis which at-
tempts to reconstruct the conditions in ancestral societies (Walker,
Hill, Flinn, & Ellsworth, 2011).
In the same vein, the patterns of mating prevalent in contemporary
agropastoral societies are likely to have been prevalent in ancestral
agropastoral ones (Apostolou, 2010b). This hypothesis is corroborated
by evidence from the historical record. More specically, a study of 16
historical societies found that the prevailing patterns were of strong
parental control over the mate choices of children, particularly daugh-
ters (Apostolou, 2012a,b).
Overall, the anthropological and historical records indicate that if
aforced-sex mating strategy has indeed evolved, this took place in a
context where mating was regulated and sexual access to women
was controlled by their parents. For a forced-sex mating strategy to
be the outcome of an evolved psychological mechanism, it must
have recurrently generated reproductive benets for the ancestral
men who followed it (McKibbin, Shackelford, Goetz, & Starratt,
2008). Therefore, the next step is to identify the benets of this strat-
egy in the context of human evolution.
3. The evolution of rape
3.1. Circumventing parental choice
When they look for sons-in-law, parents are after men who are
endowed with qualities which are benecial for them. Evidence from
contemporary and historical societies indicates that parents are inter-
ested in nding sons-in-law who have a high resource-generating
capacity, come from good families, control wealth, and have a good
character (Apostolou, 2010a, 2012a,b; Borgerhoff Mulder, 1988;
Koster, 2011). Men who lack desirable qualities such as social status
and nd themselves in a context where mating is regulated, suffer a
considerable reproductive disadvantage as they are likely to be exclud-
ed from mating or have to settle for women of a low mate value.
In more detail, parents with daughters of high mate value (e.g.,
attractive and young) are not going to be willing to give them as
wives to men of lower mate value (i.e., men who lack desirable traits).
Accordingly, if a man of low mate value aspires to meet parental
approval, he needs to address parents whose daughters also have a
low mate value (i.e., are older, unattractive, have children from previ-
ous marriages, etc.), and who are thus more willing to accept him as a
son-in-law. In effect, this man will suffer considerable tness losses as
he will have to settle for a woman of low mate value or opt out from
the reproductive process.
There are two related factors working with parental choice which
act to reduce low mate value men's ability to attract desirable wives.
One is polygyny, which is practiced in the majority of pre-industrial
societies and acts to exclude low status men from obtaining repro-
ductive access (Blood, 1972). The reason is that high mate value
men are able to attract multiple wives, leaving those at the bottom
of the hierarchy single. In the same vein, hypergyny, that is, women
marrying up the social hierarchy, a common nding in many socie-
ties, pulls women out of the lower classes, leaving many low-status
men without wives (Boone, 1986).
In this context, then, a forced-sex mating strategy can reduce the
reproductive costs that a man is likely to suffer by circumventing pa-
rental choice, giving sexual access to women of high mate value,
women that these men could not have accessed otherwise. This pre-
dicts that rapists are predominantly young men of low mate value,
which appears to be so (Thornhill & Palmer, 2000; Thornhill &
Thornhill, 1983). This predicts further that the victims of rape should
predominantly be high mate value women that these rapists could
not have accessed otherwise. Consistent with this prediction, the ma-
jority of rape victims are usually young women at the peak of their
fertility (Greeneld, 1997; Kilpatrick, Edmunds, & Seymour, 1992;
Thornhill & Palmer, 2000).
Parents prefer as in-laws individuals who have a high resource ac-
quisition capacity and control wealth (Apostolou, 2010a; Borgerhoff
Mulder, 1988). Accordingly, when they nd themselves with a
daughter of high mate value, they demand a high bridewealth (i.e.,
the wealth that the man has to pay for the marriage to proceed) to
ensure that their prospective son-in-law satises these properties
(Apostolou, 2008a). To get these resources a man relies on the
support of his family (Goody & Tambiah, 1973). Moreover, a man's
2M. Apostolou / Aggression and Violent Behavior xxx (2013) xxxxxx
Please cite this article as: Apostolou, M., The evolution of rape: The tness benets and costs of a forced-sex mating strategy in an evolutionary
context, Aggression and Violent Behavior (2013),
wealth is also determined by the wealth he receives from his parents,
usually in the form of inheritance (Hartung, 1976). Thus, a man's
wealth status is to a large extent determined by his family resources.
Men with older brothers are in a disadvantageous position to
claim family resources so they have to settle for low mate value
women or leave the reproductive process altogether (e.g., go into
the Church). There are various reasons for this, one being that older
brothers, by arriving rst, have an advantage over those born later.
For instance, older brothers may have already exploited the family's
resources before younger brothers are in a position to make a claim.
Primogeniture, practiced in many societies, means further that little
wealth passes to younger brothers.
Overall, men with older brothers usually have little wealth at their
disposal that they can divert to reproduction. In turn, this means that
it pays more for a man with older brothers than a rst-born or only
son to follow a forced-sex strategy. This suggests that there will be an
older brother effect, with the probability of following a forced-sex mat-
ing strategy being positively related to the number of older brothers a
man has.
Consistent with this prediction at least three studies have found
an older brother effect. To begin with, Lalumière, Harris, Quinsey,
and Rice (1998) correlated birth order with an overall phallometric
index of deviant sexual interests for a group of rapists, and found
that the degree of deviant response was positively related to the
number of older brothers, but not to the number of older sisters. Sim-
ilarly, Lalumiére et al. (2000) investigated the relationship between
birth order and sexual aggression against women in a sample of com-
munity males who reported having engaged in sexual aggression
with adult women and rapists from secure institutions. Their sample
also included community males who did not report having engaged
in sexual aggression. They found that the number of older brothers,
but not the number of older sisters or younger siblings of either sex,
signicantly predicted rapist versus non-rapist group membership.
Another study employed a sample of offenders detained in a medi-
um secure psychiatric unit in the United Kingdom which was comprised
of men with sexual convictions and men with non-sexual violent con-
victions (MacCulloch, Gray, Phillips, Taylor, & MacCulloch, 2004). It
was found that fraternal birth order was signicantly correlated
with the number of sexual convictions; however, no association was
found between fraternal or sororal birth order and violent convictions
in either the sex offender or violent offender group. Two more studies
found an older brother effect on sexual aggression with the effect ap-
proaching, but not passing, the signicance level (té, Earls, &
Lalumiére, 2002; Langeving, Langeving, & Curnoe, 2007).
It is important to note that the byproduct hypothesis of rape also
predicts that rapists are going to be of low mate value and their vic-
tims of high mate value (Thornhill & Palmer, 2000). What it does
not predict is that the number of older brothers increases the proba-
bility of following a forced-sex mating strategy. The presence of the
older brother effect therefore constitutes evidence in support of the
hypothesis that a forced-sex mating strategy is the product of an
evolved psychological mechanism and not a byproduct of other
3.2. Circumventing female choice
In societies where mating is regulated, women also have space to
exercise mate choice. For instance, they can do this in extramarital re-
lationships or in later marriages when their parents have died
(Apostolou, 2010b). Consequently, a man can address female choice
directly. Yet, women are after men with desirable traits such as high
resource acquisition capacity and physical attractiveness (Buss,
2003). This indicates that a man who lacks these qualities is unlikely
to be able to meet pass through female choice if he addresses high
mate value women. He will be more successful, however, if he ad-
dresses low mate value women, such as older ones, who are less
likely to receive offers from men of high mate value; however, this
will not increase his tness much as the reproductive years of these
women have already been or will soon be exhausted.
A man is expected to come across female choice also within mar-
riage. In particular, a man's mate value may decline if, for instance, he
suffers an injury from a ght, or experiences a status loss. This will
make his wife see him as a less desirable mate. In addition, in a con-
text where mating is regulated, a man may successfully pass through
parental choice, but this does not mean that he will immediately gain
sexual access to his wife, as the latter may refuse to allow him to do
so. For instance, a daughter who is married to a man she nds physi-
cally repulsive with an unattractive personality may refuse him sexu-
al access. This is a likely scenario given that when parents choose
spouses for their children they give less weight to traits such as beau-
ty and exciting personality than their children desire (Apostolou,
2008b; Buunk et al., 2008).
In all of the cases above, a forced-sex mating strategy can provide
tness benets by enabling men to circumvent female choice. The fe-
male choice within marriage cases predict further that rape would
also take place within marriage. Consistent with this prediction, be-
tween 10% and 26% of women report experiencing marital rape
(Russell, 1990; Watts, Keogh, Ndlovu, & Kwaramba, 1998). It is fur-
ther predicted that rape will be more likely to take place when the
mate value of the husband decreases (e.g., he loses his job) or the
mate value of the wife increases (e.g., she loses weight). To the
knowledge of the authors, this has not been examined, but the litera-
ture indicates that sexual and non-sexual spousal violence are
occasioned by sexual jealousy and impeding marital separation
(Mahoney & Williams, 1998; Thornhill & Palmer, 2000). As it is usual-
ly the case that women whose husband has experienced a mate value
decrease seek partners outside marriage or divorce (Buss, 2000), this
can be considered evidence in favor of this hypothesis.
Finally, in societies where marriages are arranged, rape within
marriage enhances the strength of parental choice as a sexual selec-
tion force because it makes the choices of parents on their daughters
consequential. This predicts that in these societies the parents of a
man may prompt him to force sex on his wife if she refuses, and the
parents of the bride may also encourage or at least accept such action.
This prediction also remains to be examined.
In a pre-industrial context, a forced-sex mating strategy can pro-
vide considerable reproductive benets to low mate value men by en-
abling them to circumvent parental and female choice. This strategy is
not of course cost-free or else most men would adopt it most of the
time. In particular, a rapist is likely to meet the erce reaction of a
woman's parents and other kin (see below), he is likely to meet the
resistance of the woman (which might result in injury), and he is like-
ly to meet the retaliation of the woman, especially in the case of mar-
ital rape. There are, however, instances where this strategy can
circumvent parental and female choice at low cost for the men who
adopt it.
3.3. Opportunistic sexual access
Pre-industrial societies are not peaceful, warfare and raids are
being common among them (Ember & Ember, 1995). There is consid-
erable variability among societies in the frequency of warfare and
hostilities. Some are warlike, such as the Spartans in Ancient Greece
and the Yanomamo in contemporary South America, whereas others
are much more peaceful like the !Kung in South Africa. Even in the
latter societies, however, wars and raids are not unheard of, but sim-
ply less frequent (Lee, 1979). Actually, warfare is found in the major-
ity of pre-industrial societies (Ember & Ember, 1995), which hints
that it would also have been present during most of human evolu-
tionary time, a suggestion which is supported by the historical and
archeological records (e.g., Bowles, 2009; Lambert, 2002).
3M. Apostolou / Aggression and Violent Behavior xxx (2013) xxxxxx
Please cite this article as: Apostolou, M., The evolution of rape: The tness benets and costs of a forced-sex mating strategy in an evolutionary
context, Aggression and Violent Behavior (2013),
War and raids give the opportunity to men of low mate value to
circumvent female and parental choice without having to suffer con-
siderable costs. In particular, the rape of a woman is likely to result in
retaliation from her kin, her husband, and herself. In war, however,
such retaliation is minimal since parents may have been killed
or wounded, and hostilities are usually against a different group,
which means that after their conclusion there will be no interaction
between the victim, her kin and the rapist, and there will be few
chances of him being identied.
For the same reasons, war gives the opportunity to men of moder-
ate and high mate value to gain reproductive access to women at
minimum cost. Note that, in a peacetime scenario, although these
men can pass through the parental and female choice barrier, this
usually involves a considerable cost. For instance, a man has to com-
mit substantial investment such as the payment of the bridewealth
(Goody & Tambiah, 1973) so as to be allowed access by her parents.
In a wartime scenario, however, a man who follows a forced-sex mat-
ing strategy does not need to bear these costs, while at the same time
retaliation costs are minimal.
In effect, war provides the opportunity to men, irrespective of
their mate value, to circumvent parental and female choices at a min-
imum cost. A mechanism that enables a forced-sex mating strategy
allows men to reap these opportunities. In other words, warfare
gives tness benets to those following a forced-sex mating strategy,
and these benets can be quite substantial; for instance, during
Rwanda's civil war, as many as 35% of 304 rape victims surveyed
were likely to have become pregnant (McKinley, 1996).
Wartime is not the only situation where the opportunity to cir-
cumvent parental and female choice at a minimum cost is present.
Other instances include a man nding a woman who is unprotected
and has no family or husband to revenge her rape, nding himself
in a situation where it is unlikely that he will be identied as the per-
petrator, and nding himself in a situation where the victim is unlike-
ly to go public (e.g., owing to her youth, weak character, and mental
In summary, during the period of human evolution, there were
considerable tness benets for men who adopted a forced-sex mat-
ing strategy in instances where they found themselves with a low
mate value and where the costs of following this strategy were low.
These tness benets favor the evolution of a behavioral mechanism
that will enable this strategy to be followed. Such a mechanism can be
predicted to work as follows: The lower the perceived risk of rape, the
higher the probability that a forced-sex strategy will be adopted, with
a moderating factor being a man's own mate value. Thus, men of
lower mate value will be willing to follow this strategy even if the
risks are relatively high, whereas men of high mate value will do so
only if they perceive the risks to be low.
Finally, one implication of the risk-assessment aspect of the
forced-sex mechanism is that it is likely to increase the probability
of rape within marriage. The reason is that a society is less likely to
condemn this act as it is usually believed that a woman should not
deny sexual access to her husband. For instance, until very recently,
in many Western societies it was not considered a crime if a man
forced his wife to have sex with him (Bergen, 1996; Russell, 1990).
Similarly, parents and kin are unlikely to retaliate, especially if they
are the ones who have chosen the husband. The reason is that this be-
havior not only does not harm parents' interests, but also can actually
promote them since it makes their in-law choices consequential.
4. Parental anti-rape mechanisms
Rape, irrespective of whether it is the product of an evolved mech-
anism or a byproduct of other evolved mechanisms, is costly for par-
ents. Rape can compromise the scarce reproductive resource (i.e., the
female), which parents control. The mate value of a daughter who is
raped is considerably reduced given that men value chastity in a
woman (Buss, 2003), which, in turn, means that parents can now
only attract a less desirable in-law. Moreover, her parental invest-
ment is likely to be committed through pregnancy to a man of
whom her parents probably do not approve (because if they did, he
would not rape her but he would ask them for her in marriage), or
who is not willing to commit to a relationship (rape is a short-term
mating strategy). Rape is also likely to result in physical injuries and
permanent scars or handicaps that decrease further the mate value
of a daughter. Rape may even result in the death of a daughter with
detrimental tness consequences for her parents.
In effect, the existence of a forced-sex mating strategy and its associ-
ated costs exercise considerable pressure on parents to nd ways to min-
imize them. One such way is for them to guard their daughters closely,
which in many societies, takes the form of chaperoning. Among the
Sacree hunters and gatherers in North America: Mothers kept the
strictest watch over their unmarried daughters, and never allowed
them to sleep or to wander away alone(Diamond, 1938, p. 22).
Purdah is another way for parents to protect themselves from
rape. This institution can take two forms: the physical segregation
of the sexes and the concealment of women's bodies. With regard
to the latter, one way to prevent their daughters from receiving
unwanted attention, is for parents to force them to cover their head
when they are in public places (i.e., veiling) (Shirazi, 2001). Another
form of purdah is keeping women at home and not allowing them
out of the house. For instance, in Classical Greece, women were con-
ned to a special compartment of the house, the gynaikonitis, usually
located on the upper oor (Flacelière, 1965).
As rape jeopardizes the interest of parents, social structures that
have evolved to serve different purposes are also likely to have been
shaped in a way that promotes rape prevention. For example, the sec-
ular law in most societies prescribes heavy punishment for rape. In
Classical Athens, the rape of a free Athenian woman was considered
a legal crime against her father or husband and was punishable by a
ne of 100 drachmas (Tetlow, 2005). This is also the case with divine
law. For instance, in the Bible it is stated: But if in the open country
a man meets a young woman who is betrothed, and the man seizes
her and lies with her, then only the man who lay with her shall die
(Deuteronomy 22:2528).
Rape is found in almost all known human societies (Palmer, 1989;
Rozée, 1993), which indicates that it must have been present in an-
cestral human societies as well. This means that during most of
human evolution, evolutionary pressures have been exerted on par-
ents to protect themselves from suffering the costs of rape. These
pressures are likely to have molded parental mechanisms that
would decrease the probability that their daughters would be raped.
No research has attempted so far to identify such mechanisms; still,
it can be argued that parents will be interested in closely guarding
their daughters when rape is consequential and when it is more likely
to occur.
Accordingly, it is reasonable to assume that parents would be
more interested in guarding their daughters after puberty than before
it. Similarly, parents should be more interested in guarding their
daughters if the latter are good-looking than if they are not. In addi-
tion, parents may discourage their daughters from wearing revealing
clothing or insist that a male relative accompanies their daughters or
sisters at night (McKibbin, Shackelford, Miner, & Liddle, 2011).
The presence of parental anti-rape mechanisms places evolution-
ary pressure on men to counter-evolve adaptations that will enable
them to deal effectively with these mechanisms. Such an adaptation
is likely to be a pre-disposition to assess a woman's family situation.
That is, a forced-sex strategy will not be particularly effective if a
woman has both parents around and also many brothers to protect
her. Therefore, potential rapists may target vulnerable women who
have no family or whose relatives are too weak to guard them, and
avoid women who come from powerful families, or who have rela-
tives near them to protect them. This leads to a further prediction
4M. Apostolou / Aggression and Violent Behavior xxx (2013) xxxxxx
Please cite this article as: Apostolou, M., The evolution of rape: The tness benets and costs of a forced-sex mating strategy in an evolutionary
context, Aggression and Violent Behavior (2013),
that rapists will be more willing to target women who live in big cities
away from their families than those in rural areas or in pre-industrial
societies where their families are nearby.
The close guarding of women and the parental anti-rape mecha-
nisms make a forced-sex mating strategy a costly business. Neverthe-
less, the cost of exclusion from access to high mate value women
should be higher to justify the costs of this strategy. In other words,
if, on average, the benets of following this strategy did not outweigh
its costs, such a strategy would have been eliminated by evolutionary
forces. The fact that it has not, indicates that it brings or it has brought
tness benets which exceed or have exceeded tness costs.
5. Forced-sex mating strategy across cultures
5.1. Forced-sex mating strategy in agropastoral and in hunting and
gathering societies
Societies which base their subsistence on agriculture and animal
husbandry produce more wealth than societies which base their sub-
sistence on hunting and gathering. This has several implications for
the tness benets of a forced-sex mating strategy. One such implica-
tion is that in agropastoral societies, parents have more to lose than
those in foraging societies if the mate value of their daughter is
compromised (Apostolou, 2010b). This is because in the former case
parents forfeit the opportunity to arrange a good marriage which is
likely to equate with losing access to considerable resources, some-
thing that does not happen in the latter case given that hunting and
gathering societies produce little wealth.
Consequently, parents have a stronger incentive to guard their
daughters in agropastoral societies and are likely to retaliate more harsh-
ly if any attempts are made to compromise the mate value of the ir female
relatives. Consistent with this hypothesis, female-guarding institutions
such as the purdah are found predominantly in agropastoral societies
(Apostolou, in press). In effect, the tness benets of a forced-sex mating
strategy are going to be lower in an agropastoral context than in a forag-
ing one, since in the former, it will be more difcult to circumvent paren-
tal choice, and the cost of doing so is likely to be higher.
This is not the end of the story, however. Analysis of the anthropo-
logical record indicates that warfare is more frequent in agricultural
societies than in hunting and gathering ones (Nolan, 2003). This is
to be expected given that more wealth is produced in the former
than in the latter, which gives an incentive to one group to attempt
to take control of the resources of the other. More frequent or
larger-scale warfare means more low-cost reproductive opportuni-
ties, which, in turn, indicates more tness benets accruing from a
forced-sex mating strategy.
On the basis of these arguments, it can be predicted that in
agropastoral societies, the frequency of peacetime rape will be
lower and the frequency of wartime rape higher. A further prediction
is that the transition from foraging to agropastoralism approximately
10,000 years ago should have resulted in a lower peacetime rape fre-
quency and a higher wartime rape frequency.
5.2. Forced-sex mating strategy in post-industrial societies
In order to protect themselves from the costs of the forced-sex
mating strategy, parents have developed specic protection mecha-
nisms that reduce the chances that their daughters will be raped,
and these mechanisms can be effective. For instance, Figueredo et
al. (2001) found that the presence of adult male kin living nearby de-
creased the likelihood of a female relative being raped. Similarly,
Kanin (1957) found that young women who grew up with older
brothers were less likely to become the victims of rape.
Women themselves have also evolved anti-rape mechanisms. In
particular, in a number of studies, women were found to change
their behavior over the ovarian cycle by selectively reducing activities
such as walking alone in the park or getting drunk when out, activi-
ties that might expose them to the risk of sexual assault at times
close to ovulation (Bröder & Homann, 2003; Chavanne & Gallup,
1998; McKibbin & Shackelford, 2011; McKibbin et al., 2009). In addi-
tion, rape is associated with considerable emotional pain for the vic-
tim; this pain is probably an adaptation that encourages women to
avoid any situations that may lead to similar incidents in the future
(Thornhill & Thornhill, 1990). Note that these ndings constitute fur-
ther evidence that rape was present during human evolutionary time;
if rape were only a modern phenomenon there would not have been
sufcient time for such mechanisms to evolve.
The evolutionary forces that have shaped rape protection mecha-
nisms worked primarily on parents and not on their daughters. That
is, women were under the control of their relatives and later on of
their husbands, who were mainly responsible for guarding them
against rape. Consequently, evolution would not have prepared
women adequately for a modern world where, after reaching sexual
maturity, they are likely to be on their own for several years before
getting married. This indicates that in a post-industrial context,
where mating is not regulated and parents are not there to guard
their daughters, women may be more vulnerable to rape.
What makes things worse is that, because of modern labor market
demands and labor mobility, women are likely to move to a different
city or even to a different country from the one where their parents
and relatives live, which renders them even more vulnerable to
rape. The high incidence of rape in Western societies (Kilpatrick et
al., 1992) may be partially explained by the inadequacy of women's
rape-protection mechanisms and the fact that they usually live
away from their kin.
Overall, because during most of human evolution that young
women have been protected by their parents from being raped,
there may have been insufcient evolutionary pressures on them to
evolve anti-rape mechanisms good enough to protect them in a
free-mate-choice world.
6. General discussion
Across human cultures, certain men under certain conditions
adopt a forced-sex mating strategy. This paper supports the hypothe-
sis that this strategy constitutes a behavioral expression of an innate
mechanism that increases tness by enabling men to circumvent pa-
rental and female choice and exploit low-cost reproductive opportu-
nities. This argument is consistent with anthropological and historical
evidence which indicates that there were recurrent tness benets
for men who adopted this strategy.
One prediction that follows from this hypothesis is that this mech-
anism should be present in most men; that is, a forced-sex mating
strategy is a conditional strategy that may be employed by most
men under specic circumstances (McKibbin et al., 2008; Shields &
Shields, 1983; Thornhill & Palmer, 2000). Consistent with this predic-
tion, in one study, at least one-third of men admitted that they would
rape under specic conditions (Malamuth, Huppin, & Paul, 2005).
Further support for this prediction comes from evidence of war rape
which indicates that a forced sex-mating strategy is adopted by a
large proportion of men who engage in it (Smuts, 1996). For instance,
the number of Red Army rapes in Berlin at the end of World War II
were estimated to be around 1,000,000 (Grossman, 1999). These
were obviously not the doing of a small minority of Soviet soldiers.
The circumstance likely to trigger the adoption of this strategy is if a
man nds himself lacking the desirable traits that will enable him to
compete successfully in the mating market, and if he perceives the risk
of doing so to be low. With regard to the former, neurodevelopmental
problems (e.g., brain damage, learning disabilities, and low IQ) or poor
social conditions (e.g., lack of family resources, low birth order, and ex-
not easily acquire resources and mating success by conventional
5M. Apostolou / Aggression and Violent Behavior xxx (2013) xxxxxx
Please cite this article as: Apostolou, M., The evolution of rape: The tness benets and costs of a forced-sex mating strategy in an evolutionary
context, Aggression and Violent Behavior (2013),
means. These clues may trigger anti-social tactics including a forced-sex
mating strategy (Lalumiére, Harris, Quinsey, & Rice, 2005). This predicts
that anti-social tactics and a forced-sex mating strategy will co-occur,
which seems to be the case (Lalumiére et al., 2005).
The risk-assessment argument predicts further that this strategy is
likely to be followed when there is a considerable status difference
between the perpetrator and the victim, a scenario that will make
the former believe that the latter will not go public or if she does, it
will have no serious consequences for him. This accounts for the
fact that men of high mate value commit rape. They do so not because
they cannot get desirable woman otherwise but because their status
makes the cost of this act small or non-existent. For instance, General
Gaddain Libya raped schoolgirls that were kidnapped to serve him
as sex slaves (Cojean, 2012). He did so without consequences.
There are certain ndings which may be interpreted as evidence
against the proposed hypotheses. In particular, sexual offenders usu-
ally report being sexually experienced and having had many consen-
sual sexual relationships before conviction (Gebhard, Gagnon,
Pomeroy, & Christenson, 1965; Lalumiére et al., 2005). Still, the pri-
mary hypothesis offered here is that a forced-sex mating strategy en-
ables low mate value men to get sexual access to high mate value
women. That is, the evolutionary problem that this strategy solves is
how to gain sexual access to high mate value women not women in
general. Therefore, being sexually experienced or having access to
consensual sex is not evidence against this hypothesis. Such evidence
would be if low mate value rapists had many consenting sexual rela-
tionships with women of high mate value. This remains to be investi-
gated, but given female and in in-law preferences, it is unlikely.
Moreover, it has also been argued that a forced-sex mating strate-
gy enables men irrespective of their mate value to gain sexual access
to women at low or no cost. This cost is not always non-existent,
however, or men may simply misjudge it. In consequence, a high
mate value man may be arrested and convicted for engaging in this
act (e.g., the boxer Mike Tyson). Such a man, however, is likely to
have had many consensual sexual relationships with attractive
women before the conviction. So, a small proportion of convicted rap-
ists are likely to be high mate value men who have had many consen-
sual sexual relationships with high mate value women before their
There are other explanations that fall outside the evolutionary
framework which have attempted to account for rape, the most
prominent one being that rape is a way for men to secure and main-
tain power over women (Brownmiller, 1975). In this view, rape is not
sexual in nature; that is, those engaging in it are not really after sexual
intercourse, but want to exercise or exhibit power. Actually, this is the
explanation that most psychologists offer when asked about the
causes of this act, and it is the explanation that has been adopted by
the general public.
This account of rape is problematic in many respects, however,
one being that it generates predictions which do not t the recorded
patterns of rape. For example, if rape is not about sex but about
power, it can be predicted that rape victims will be older high status
women and not young ones at the peak of their fertility, which is not
the case (Thornhill & Palmer, 2000). Similarly, studies of patterns of
rape nd escalation in offense severity to the level of intercourse,
strongly suggesting that rape is a reproductive strategy rather than
a power strategy (Britt, 1996).
Another issue with these approaches is that they do not take into
consideration the evolved nature of human behavior. Rape inicts
substantial tness costs on women and their parents, whereas it be-
stows considerable tness benets on offenders. This means that
rape is unlikely to fall outside the radar of evolution. That is, rape is
not an act that is evolutionary neutral, and consequently its explana-
tion cannot fall outside the evolutionary framework.
Although an evolutionary approach to rape can be fruitful, there
are also pitfalls, one being the failure to take into consideration the
context in which rape evolved. Accordingly, it has been suggested
that a forced-sex mating strategy aims predominantly to circumvent
female choice (Thornhill & Palmer, 2000). This is not plausible, how-
ever, as anthropological and historical evidence indicates that during
the period of human evolution women were controlled by their par-
ents (Apostolou, 2012b).
This paper has argued that a forced-sex mating strategy is not a
byproduct of other mechanisms, but is an adaptation which evolved
to enable men of low mate value to bypass parental and female
choice, and enable men, irrespective of their mate value, to exploit
low-cost mating opportunities; a hypothesis that ts well with the
anthropological and historical records. It also ts well with observed
rape patterns including the older brother effect which is not
accounted for by other theories. In addition, this framework offers
several insights on rape and generates several testable hypotheses that
future research should address. For instance, it suggests that parents
are equipped with anti-rape mechanisms that enable them to protect
their daughters from men who follow a forced-sex mating strategy.
It has to be said, nevertheless, that the proposed theoretical
framework does not account for all forms of rape in all instances.
For example, it does not negate the possibility that rape occurs also
as an outcome of psychopathology. It is argued here that rape is a re-
productive strategy and thus instances where the rape is followed by
the murder of the victim fall outside this framework; their causes are
probably pathological. Similarly, the present framework does not ac-
count for individual differences in men adopting this strategy. For in-
stance, in wartime not all men rape. This means that additional
theoretical and empirical work is required if all aspects of this strate-
gy are to be identied. Any such attempts, however, should take into
consideration the context in which this strategy evolved: namely, the
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