Evolutionary Behavioral Sciences
Sex Differences in Serial Killers
Marissa A. Harrison, Susan M. Hughes, and Adam Jordan Gott
Online First Publication, January 24, 2019. http://dx.doi.org/10.1037/ebs0000157
CITATION
Harrison, M. A., Hughes, S. M., & Gott, A. J. (2019, January 24). Sex Differences in Serial Killers.
Evolutionary Behavioral Sciences. Advance online publication.
http://dx.doi.org/10.1037/ebs0000157
Sex Differences in Serial Killers
Marissa A. Harrison
Penn State Harrisburg
Susan M. Hughes
Albright College
Adam Jordan Gott
Penn State Harrisburg
Research directly comparing empirical data of the behaviors and crimes of male serial
killers (MSKs) versus female serial killers (FSKs) within one study is nonexistent. This
study sought to make such a direct comparison. We examined sex differences in serial
murder that may be byproducts of ancestral tendencies. Specifically, we proposed and
tested a “hunter-gatherer” model of serial murder. Using the mass media method to
collect archival data, we obtained information about 55 MSKs and 55 FSKs (matched
for age of first murder) who committed their crimes in the United States from 1856 to
2009. We found that MSKs more frequently act as “hunters,” stalking and killing
targeted strangers in dispersed areas, while FSKs more frequently are “gatherers,”
killing those who are around them and familiar to them and gaining profit from their
crimes. We also documented other sex differences between serial murderers. We
discuss these findings from an evolutionary psychological perspective.
Public Significance Statement
We documented sex differences in the crimes and motives of male serial millers
(MSKs) and female serial killers (FSKs). A direct comparison of data via an
evolutionary lens suggests a “hunter-gather” model of serial murder. MSKs tend to
“hunt” and stalk unfamiliar victims, often with a sexual motive, keeping trophies of
their crimes. FSKs tend to “gather” victims by killing people closest to them, often
relatives, commonly to collect/gather profit. Law enforcement may consider evi-
dence of sex differences in serial murderers for crime solution and prevention.
Keywords: serial killer, sex differences, male, female, hunter-gatherer
Serial killing refers to the premeditated, in-
tentional killing of three or more victims, with a
cooling-off period between killings of at least
one week (M. A. Harrison, Murphy, Ho, Bow-
ers, & Flaherty, 2015; Hickey, 1991; S. T. Hol-
mes, Hickey, & Holmes, 1991; Keeney &
Heide, 1994). The horror of serial killings cap-
tures public attention considerably (Haggerty,
2009; M. A. Harrison et al., 2015; Keeney &
Heide, 1994). However, empirical research re-
garding serial murder is relatively rare, likely
because it is a rare phenomenon. Only a small
percentage of murders in the United States are
serial killings (Fox & Levin, 1998; Hickey,
2010). In addition, serial murders have a low
case clearance rate (percentage of solved
crimes; Miller, 2012), and clinical researchers
have limited access to offenders (Keeney &
Marissa A. Harrison, Psychology Programs, Penn State
Harrisburg; Susan M. Hughes, Psychology Department, Al-
bright College; Adam Jordan Gott, Psychology Programs,
Penn State Harrisburg.
The authors thank E. Murphy, A. Pavoncello, T. Bowers,
and Penn State Libraries for their kind assistance.
Correspondence concerning this article should be ad-
dressed to Marissa A. Harrison, Psychology Programs, Penn
State Harrisburg, Olmsted W311, 777 West Harrisburg
Pike, Middletown, PA. E-mail: mah52@psu.edu
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This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.
Evolutionary Behavioral Sciences
© 2019 American Psychological Association 2019, Vol. 1, No. 999, 000
2330-2925/19/$12.00 http://dx.doi.org/10.1037/ebs0000157
1
Heide, 1994). Very few authors have attempted
to understand and shed light on serial murder
using an evolutionary psychological frame-
work; we endeavor to do so in the present
article.
Daly and Wilson (1988, 1997) were among
the first scholars to apply evolutionary theory
to inform our understanding of murder. They
suggested that criminal homicide may be an
extreme byproduct of sex-specific self-
interests that have evolved over many millen-
nia to maximize fitness. In support of an
evolved view of murder, Gómez, Verdú,
González-Megías, and Méndez (2016) exam-
ined a large, diverse sample of humans and
other animals and found lethal, conspecific
violence in nearly 40% of the species studied.
They estimated that 2% of human deaths are a
result of interpersonal violence, inferring that
this percentage is similar to what manifested
in the common phylogenetic ancestor of apes
and in prehistoric peoples. Other scholars
have suggested this percentage may be even
higher over the many millennia of human
existence in prehistoric and contemporary
nonstate societies (Gat, 2006; Keeley, 1996;
Pinker, 2011). Evidence thus suggests modern
humans have a phylogenetic signal for lethal
violence (Gómez et al., 2016). Archeological
records provide convincing evidence of early
humans dying at the hands of conspecifics
(Duntley & Buss, 2011; Sala et al., 2015).
This allows inference of murder as a contin-
uous event in hominid evolution and informs
the capacity for lethal violence in modern
humans (Duntley & Buss, 2011; Gómez et al.,
2016; Kelly, 2005; Pagel, 2016). Other re-
searchers have also documented conspecific
murder in nonhuman animals (e.g., chimpan-
zees, wolves, prairie dogs; Hoogland &
Brown, 2016; Wrangham, 1999).
Although evolutionary theory can be power-
ful for predicting and explaining behavior
(Buss, 1998, 2009), the caveat exists that evo-
lutionary theory likely cannot explain murder in
toto. As Neese (2005) explained, when consid-
ering individual variation in a trait or behavior,
such as that seen in physical violence and mur-
der, we face the challenge of understanding
multiple genetic and environmental contribu-
tions. Daly and Wilson (1997) also urged the
consideration of social settings in understanding
the development and maintenance of violent
tendencies.
Daly and Wilson (1997) emphasized that
seemingly irrational behavioral choices, such as
committing murder, are subject to the influence
of complex, evolved, unconscious mechanisms.
Duntley and Buss (2012) pointed out that mur-
derers are not consciously aware of the ultimate
reasons for their behavior. That being said, it
should be stressed that even if serial murder is a
manifestation and/or variant of unconscious,
evolved tendencies, classifying a behavior as an
adaptation does not equate that behavior to be-
ing “good” or “correct,” and murder is nowhere
condoned. A drive that is unconscious cannot be
an excuse for the permission of heinous acts.
All societies with written laws identify killing
as criminal (Duntley & Buss, 2011).
“Hunter-Gatherer” Model of Serial Murder
In the present article, we put forth the argu-
ment that male serial killers (MSKs) are theo-
retical “hunters” of victims and female serial
killers (FSKs) are theoretical “gatherers” of vic-
tims. That is, MSKs more frequently kill strang-
ers they stalk, traveling distances to “hunt” and
kill. In contrast, FSKs more frequently kill those
around them, figuratively “gathering” victims
who are familiar to them, staying in one place to
kill. These differences may stem from sex-
specific tendencies derived from labor divisions
in the ancestral environment whereby men
hunted animals as prey and women gathered
nearby grains and plants for food (Bradley &
Moore, 1996; Lovejoy, 1981; Silverman &
Eals, 1992). Some researchers estimate that
humans lived as hunter-gatherers for 95% of
species history (Hill et al., 2011). It has long
been argued that the repeated physical, social,
and ecological elements of the ancestral en-
vironment gave rise to adaptations to maxi-
mize fitness under those conditions, and con-
temporary human behavior still reflects this
under similar circumstances (Bowlby, 1969;
Tooby & Cosmides, 1990). Stated another
way, when animals live under certain condi-
tions for a long period of time, they geneti-
cally adapt to those environments (Pagel,
2016). It follows from this that in identifying
intended victims of serial murder, it may be a
product of evolved psychology that women
2 HARRISON, HUGHES, AND GOTT
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look to those who are known to them in a
familiar setting as a gatherer would, and men
look for strangers, engaging in a pursuit sim-
ilar to a “hunt,” finding unknown victims in a
more geographically disbursed area.
M. A. Harrison and colleagues (2015) argued
that sex differences in motives between serial
murderers follow evolved, sex-specific mating
strategies. They documented that among female
serial murderers, the most common motive for
killing was financial gain, corroborating the
findings of previous researchers (Hickey, 2010;
Keeney & Heide, 1994). Other researchers
(Hickey, 2010; R. M. Holmes & Holmes, 2010)
have asserted that sexual gratification is the
most common motive for male-perpetrated se-
rial murder. These tendencies follow the funda-
mental sex differences in reproductive potential.
Compared to men’s virtually unlimited supply
of sperm, women have a very limited number of
ova, cyclical gametic release, and a truncated
reproductive life span with fewer opportunities
for offspring due to internal gestation. As such,
the evolved mating psychology of women and
men is starkly different. In the ancestral envi-
ronment, to maximize genetic fitness, women
would benefit from seeking long-term, stable
partners with resources to invest in them and
their offspring, and men would benefit more
from seeking multiple mating opportunities
(Hughes & Aung, 2016; Symons, 1979; Trivers,
1972). Researchers have documented that con-
temporary men and women still seek mates in
this vein (Buss, 1998; Buss & Schmitt, 1993).
In the present article, we argue that sex differ-
ences emerge in serial murderers that reflect
these evolved tendencies.
It should be stressed that direct, empirically
driven comparisons of MSKs and FSKs are
rare. Decades ago, Keeney and Heide (1994)
executed a well-designed study of FSKs, but to
comment upon differences, they compared their
results to what was previously documented
about MSKs. This is one of the only studies of
this nature we have found in the literature. No-
tably, Keeney and Heide emphasized that “there
may be more differences than similarities be-
tween female serial killers and their male coun-
terparts” (p. 392). Thus, information is pre-
sented below separately for MSKs and FSKs
about known traits and tendencies.
Male Serial Killers as “Hunters”
We argue that, quite literally, typical MSKs
operate as hunters of their victims. Indeed, as
reported by Homant and Kennedy (2009), other
scholars have referred to MSKs as “hunters”
(Goldsworthy, 2002) and have used hunting ter-
minology to describe victim acquisition (Beau-
regard, Proulx, Rossmo, Leclerc, & Allaire,
2007; Rossmo, 1997).
The most commonly identified typology of
MSKisthehedonistic serial killer (e.g., those
seeking pleasure; R. M. Holmes & DeBurger,
1988; R. M. Holmes & Holmes, 2010), who are
known to seek and stalk unfamiliar victims in
order to derive sexual pleasure, power, and thrill
from their crimes (Miller, 2014). Stalking is
seen quite prevalently in MSKs (Hickey, 2013).
MSKs methodically select and stalk previously
unfamiliar victims, patrolling and waiting, often
for days, for the right time to attack, capture,
and force the victim into submission (Hickey,
2013; Keeney & Heide, 1994; Miller, 2012,
2014). This is predatory behavior (Mullen,
Pathé, & Purcell, 2000), recapitulating what oc-
curs during hunting in a food foraging environ-
ment. Duntley and Buss (2012) also noted that
stalking largely reflects tactics executed in hunt-
ing and warfare, including being persistent, not-
ing the routines of targeted victim, incorporat-
ing surprise, and using weapons.
Duntley and Buss (2012) maintained that if
stalking “sometimes succeeded” in increased
sexual access and therefore fitness gains over
millions of years of human evolution, selection
would have favored it as an adaptation. Stalk-
ing, attacking, and separating a woman from her
protective kin and social setting could increase
sexual exploitation opportunities and reduce
costs of coercive fitness maximization strategies
(Buss, 2005; Goetz, Easton, Lewis, & Buss,
2012). The covert approaches used by stalkers,
such as spying and documenting the routines
and social networks of their victims, can inform
exploitation and surprise attacks and can serve
to minimize retaliation (Buss & Duntley, 2008;
Duntley & Buss, 2012).
Humans and other species that hunt prey
likely possess adaptations to detect the exploit-
ability of their targets (Buss & Duntley, 2008)
and use deception and force to take advantage
of their targets (Buss & Duntley, 2008; Goetz et
al., 2012). Research has shown consensus
3SEX DIFFERENCES IN SERIAL KILLERS
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among men and women as to which women are
deemed easily victimized and sexually exploit-
able (Goetz, Easton, & Buss, 2014; Goetz et al.,
2012; Grayson & Stein, 1981; Gunns, Johnston,
& Hudson, 2002), and some men are particu-
larly attracted to exploitable women (Goetz et
al., 2012). This seems to be part of the modus
operandus of the typical MSK (Miller, 2014).
MSKs were documented to travel distances
to “forage” for victims (Hickey, 2013; R. M.
Holmes & Holmes, 2010), an activity reminis-
cent of hunting tactics. Furthermore, as a grue-
some analog, MSKs have been shown to disar-
ticulate or otherwise butcher their victims
(Hickey, 2013; Miller, 2014) as one would do to
successfully hunted game for consumption.
Male serial killers also tend to keep “trophies”
of their killings, ranging from the victim’s jew-
elry to clothing, body parts, and blood (Federal
Bureau of Investigation, 2005; Miller, 2014).
Many contemporary game hunters keep tro-
phies of their kills, such as antlers (Carpenter,
2013), just as ancestral and modern soldiers of
war have been known to keep the skulls and
other body parts of their defeated enemies as
trophies of victory (S. Harrison, 2006; Lambert,
2002).
Male-perpetrated serial murder is usually
marked by aberrant sexual activity (R. M. Hol-
mes & Holmes, 2010), and nearly a third of
MSKs have exhibited hypersexuality (Stone,
2001). MSKs may engage in sadistic sexual
behavior, including binding, torture, humilia-
tion, and mutilation. MSKs have been docu-
mented to engage in necrophilia, with some
even repeatedly visiting the victim’s decompos-
ing body for sexual contact (see Miller, 2014,
for review). This type of sexual sadism is not
characteristic of FSKs. As Farrell, Keppel, and
Titterington (2013) pointedly asserted, “Women
tend to kill quietly, preferring not to butcher and
maim. It is unlikely you would find a woman
sexually assaulting a corpse or engaging in can-
nibalistic or vampiric activities” (p. 270). Inter-
estingly, too, serial murder is frequently associ-
ated with a history of perpetrator rape and
escalates to the “ultimate violation” of murder
(Miller, 2014). Nonetheless, it should be noted
that not all “hunter” serial killers have sex with
their victims.
Male-perpetrated serial murder may be con-
sidered an extreme byproduct of fitness psy-
chology. Murderers can incur enormous costs
such as diminished status, punishment, and le-
thal retribution, and therefore Duntley and Buss
(2011) asserted that there must have been re-
current conditions in the ancestral environment
where fitness gains from committing murder
outweighed fitness losses (p. 400). They pro-
posed that murder to acquire new mates was one
such condition. As such, researchers have noted
that young adult women are the most frequent
victims of MSKs (Hickey, 1991; Miller, 2014),
which is in contrast to the rates of other murders
seen in the U.S. and worldwide, where men are
far more likely (about 80%) to be victims of
unlawful homicide (United Nations Office on
Drugs and Crime, 2013). Serial murder of a
sexual nature, then, must be a pathological vari-
ant to this approach, because even if sex is an
element of the crime, genes cannot be passed on
to subsequent generations by a murdered vic-
tim.
Buss and Duntley (2008) argued that men,
more so than women, use physical threats and
violence to attain resources, and such strategies
evolved as a result of increased competition
among men for access to women. Evidence
gathered from across cultures suggests that men
are consistently more physically aggressive
than women (Archer, 2004; Ellis et al., 2008)
and are more likely than women to inflict injury
on opposite sex partners (Archer, 2000). Male
violence is likely a recurring strategy for mate
acquisition. In the environment of evolutionary
adaptedness, females would be subjected to sex-
ual coercion by larger, more muscular, more
aggressive males (see Puts, 2010). Male-
perpetrated serial murder, which is characteris-
tically violent, sexually sadistic, and frequently
committed against women, would represent a
most extreme manifestation of these ancient
tendencies.
The crimes of MSKs are typically against
strangers (Fox & Levin, 1998; Godwin, 2000;
Schlesinger, 2007). Hickey (2010) reported that
the majority of MSKs killed strangers only,
with about another 15% killing at least one
stranger among their victims. Likewise, God-
win and Canter (1997) analyzed MSK crimes,
and in 92% of cases, the perpetrator did not
know the victim and vice versa. Hickey (2010)
noted that a typical reason that MSKs would
stalk strangers is sexual predation. Researchers
have stressed that these planned murders of
4 HARRISON, HUGHES, AND GOTT
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previously unknown victims evince a calculat-
ing, cold, predatory strategy (Yaksic, 2015).
It might be the case that men with lower mate
value would resort to violence and murder after
less costly mate acquisition tactics were at-
tempted and failed (Duntley & Buss, 2011,
2012). Of note, it was difficult to pinpoint stud-
ies documenting the income level or socioeco-
nomic status of MSKs other than one from
Stone (2001) noting that 64% of MSKs came
from lower or lower-middle class backgrounds.
The author posited that “men of meager in-
come” may be threatened by increased female
status over the past several decades (p. 13). The
fact that some MSKs brag about their crimes
(Haggerty, 2009; Vronsky, 2004) evinces a
need for status elevation.
Female Serial Killers as “Gatherers”
Whereas there is considerable research on
MSKs, research on FSKs is quite rare (M, A,
Harrison et al., 2015; Keeney & Heide, 1994),
possibly due to the fact that the number of serial
murderers who are women is also rare. Parallel
to general homicide trends, about 1 in 6 serial
killers (about 17%) are women (Hickey, 2010).
Furthermore, serial murders are estimated to
constitute less than 1% of all murders (Federal
Bureau of Investigation, 2005), and FSKs are
just a fraction of these offenders. In addition to
the limited amount of FSK cases, Schurman-
Kauflin (2000) remarked that people tend to
disbelieve that a woman could commit the hei-
nous crimes of serial murder, which may further
contribute to the dearth of investigations on
FSKs.
In line with our proposed hunter-gatherer hy-
pothesis, we argue that FSKs are theoretical
“gatherers” of victims. Whereas MSKs hunt
strangers to kill, FSKs, in a figurative sense,
“gather” victims who are near and familiar to
them. Several sources have documented how
FSKs tend to victimize people who are around
them and known to them. Farrell et al. (2013)
found that 80% of FSKs victims personally
knew their killers. Similarly, Keeney and Heide
(1994) collected data about 14 FSKs from legal
documents, correctional files, psychological
evaluations, and mass media reports and found
that at least 80% of FSKs knew their victims,
with most being in their custodial care and
related. Keeney and Heide reported that the
remaining 20% consisted of acquaintances, lov-
ers, and strangers, and because these data were
not further parsed, we can only infer that the
total percentage of victims familiar to the sam-
ple of FSKs was greater than 80%.
FSKs often target children and familiar oth-
ers who are typically vulnerable and/or under
their care (e.g., elderly, infirm; M. A. Harrison
et al., 2015; Hickey, 2013; Kelleher & Kelleher,
1998; Schurman-Kauflin, 2000). M. A. Harri-
son and colleagues (2015) showed that 72% of
FSKs killed at least one person who was under
their care and powerless to fight back, with
nearly 44% of FSKs killing their own children.
One FSK, described by U. S. newspapers in
1925 as “remorseless,” poisoned eight people
including six children, three of whom were her
own children. She is quoted as saying, “They
bothered me, so I decided to kill them” (Sioux
City Journal, 1925, as cited by “Della Soren-
son,” 2014). This FSK also told officials that
she liked to attend funerals (“This day in his-
tory,” 2018), possibly evincing some form of
mental illness.
The murder of children, the elderly, and in-
firm individuals can be considered mothering
and allomothering gone awry. Allomothering is
argued to be an evolved drive to provide care
(Hrdy, 2009). Of course, the killing of one’s
relatives, and particularly of offspring, is the
antithesis of reproductive fitness. If murderous
tendencies are in our genetic heritage, serial
murder of one’s kin is a pathological expression
of such, as is the killing of nonkin immatures
and vulnerable persons. We support the argu-
ment that serial murder is an example of an
outlier in the distribution of polygenic traits
(Wakefield, 2005). This has been argued to be
the case in other aberrant behaviors, such as
stalking (Brüne, 2003). That is, if caregiving is
the norm with most cases lying in the center of
the distribution, there will be extremes of the
trait distribution representing extremely exag-
gerated or reduced levels (Neese, 2005; Wake-
field, 2005). As such, studies have demonstrated
a high prevalence of mental illness in FSKs
(M. A. Harrison et al., 2015).
FSKs tend to stay in one place committing
their crimes. This is reminiscent of the move-
ment patterns of women in ancient and current
hunter-gatherer societies whose division of la-
bor is to locally collect fruit and berries (e.g.,
Hadza women; Marlowe, 2004). Keeney and
5SEX DIFFERENCES IN SERIAL KILLERS
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Heide (1994) found that almost all (13 out of
14) FSKs remained in one small area or place to
commit their murders and showed no evidence
of victim stalking. Farrell and colleagues (2013)
also showed that more than 44% of FSKs stayed
in their local area to commit their crimes. As
compared to a hunter who may travel long dis-
tances for prey, a gatherer would stay closer and
collects plants and fruits available around them
(Ames & Maschner, 2000).
Whereas there is commonly a sexual motive
for male-perpetrated serial murder (Hickey,
2010), studies have shown profit as a primary
motive for female-perpetrated serial murder (M.
A. Harrison et al., 2015; Hickey, 2010; Kelleher
& Kelleher, 1998; Keeney & Heide, 1994). Al-
though men are documented as more aggressive
and violent (see Puts, 2010), women can also be
violent and injurious of others. However,
Campbell (1999) has argued that female aggres-
sion is more intense in situations of acquiring
and/or defending necessary, scarce resources.
FSKs often kill a husband or other partner for
financial gain through insurance or inheritance
and move on to another partner. M. A. Harrison
and colleagues (2015) found female serial kill-
ers to be serial monogamists, who, on average,
are married twice with a range of up to seven
times, often killing husband after husband for
insurance or estate benefits and other resources.
This “gathering” of resources takes an aberrant
route but still reflects female ancestral tenden-
cies to secure provisioning for themselves and
their offspring.
The Present Study
The aforementioned evidence supports the
notion that MSKs operate as hunters and FSKs
operate as gatherers. While numerous studies
have provided valuable, converging evidence as
to the motives and crimes of male and female
serial killers, we have not seen a direct, empir-
ical, statistical comparison informing sex differ-
ences. In the present study, we directly compare
archival data of male and female serial murder-
ers (matched on age of first murder) to test the
following hypotheses supporting the viewpoint
that male serial killers are “hunters” and female
serial killers are “gatherers.”
H1: FSKs were more likely to have known
their victims than MSKs.
H2: MSKs engaged in stalking their vic-
tims prior to the murder more frequently
than had FSKs.
H3: MSKs were more likely than FSKs to
have killed beyond their birthplace and to
have killed across several states (i.e., di-
verse locations).
H4: MSKs overrepresent lower socioeco-
nomic status.
H5: MSKs more frequently had a sexual
motive to kill (i.e., a predatory hunt for
sex), whereas FSKs more frequently had a
profit motive to kill (i.e., a gathering of
resources).
In addition to these hypotheses, because data-
based comparisons of MSKs and FSKs are non-
existent as known to us, we aimed to document
other sex differences, such as number of vic-
tims, killing timespan, age of victims, sex of
victims, perpetrator relationship status at the
time of the murders, most commonly used
method of killing, mental health, judicial out-
comes, U.S. region of murders, and ascribed
killer nicknames.
Method
This study employed the mass media method
to obtain archival data on serial killers, which is
a common method used by investigators explor-
ing similar topics (e.g., Farrell et al., 2013;
M. A. Harrison & Bowers, 2010; M. A. Harri-
son et al., 2015; Keeney & Heide, 1994). We
consulted verifiable media for information
about perpetrators in the United States who
committed serial murder to the present date
(2018). We used Internet search engines to
gather information, and we also used Murder-
pedia.org as a source of names of killers and to
direct us to legitimate, reputable news sources
(e.g., Associated Press, Reuters, TV networks,
national and local newspapers). We found Mur-
derpedia entries to be 100% verifiable with
valid media sources.
In a previous study, we collected data on
FSKs who committed their crimes in the
United States, and we described these find-
ings in detail in M. A. Harrison et al. (2015).
To allow a direct comparison, we repeated
this process to find information on MSKs. We
selected serial killers who committed their
6 HARRISON, HUGHES, AND GOTT
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crimes only in the United States, because our
research team is English-speaking, U.S.-
based, and we have greater access to Ameri-
can, English-language media sources.
Because age and crime have been strongly
linked, with similar age curves for male and
female offenders (see Ulmer & Steffensmeier,
2015), we selected our sample of MSKs based
on age of first murder that matched to our sam-
ple of FSKs. Validating our selection, a paired-
samples ttest showed that there was no age
difference at first murder between our sample of
MSKs (M⫽30.36, SD ⫽10.02) and FSKs
(M⫽30.31, SD ⫽10.28), t(54) ⫽.080, p⫽
.937. There was also no difference in distribu-
tion across seven age brackets (teens, 20s, 30s,
40s, 50, 60s, 70s),
2
(6, N⫽110) ⫽5.39, p⫽
.495. To control for cohort effects, we also
looked for similarity in the years their murders
began, although a close match was not always
possible. The median year of first murder was
1974 for both FSKs and MSKs, and analysis
showed high reliability among our selection of
years of first kill among the 55 pairs of FSKs
and MSKs (␣⫽.982). Furthermore, there was
no difference in ethnicity, as the majority of
both FKSs (86.8%) and MSKs (70.9%) were
White, with others reported as Black (FSKs:
11.3%; MSKs: 23.6%), Hispanic/Latino (FSKs:
1.9%; MSKs: 3.6%), and Middle Eastern
(MSKs: 1.9%),
2
(3, N⫽108) ⫽4.45, p⫽
.216.
We validated that each reported murderer
selected for inclusion met our definition of a
serial killer. The Federal Bureau of Investiga-
tion (2005) of the United States defines serial
murder as “the unlawful killing of two or more
victims by the same offender(s), in separate
events” (p. 9). Several academics have stressed
premeditation and have defined serial murder as
three or more deceased victims (Farrell et al.,
2013; Hickey, 1991, 2010; S. T. Holmes et al.,
1991; Keeney & Heide, 1994). Therefore, we
defined serial murder as cases of the premedi-
tated, intentional killing of three or more vic-
tims, with a cooling-off period between killings
of at least one week. This excludes killings
committed by members of the military in the
course of their jobs or murders by political
assassins (cf. Keeney & Heide, 1994).
Our final sample (N⫽110) consisted of 55
female and 55 male age-matched serial killers
who committed their crimes in the United States
from 1856 to 2009. We collected information
via article content with respect to their sex,
birthplace, age when crimes began, crime loca-
tions in the U.S., motive to kill, perpetrator
relationship to victims (stranger or familiar;
blood relationship or spouse/long-term partner),
number of victims, sex of victims, age of vic-
tims, income/income category of perpetrator,
judicial dispositions, relationship status at time
of killings, method of killing, and ascribed
killer nicknames. One of the authors recorded
data for these variables, and another author ver-
ified each entry. It is important to stress that not
all information was available for all variables
for each serial murderer. Where applicable, we
report percentages based on the number of cases
for which we acquired information, and not
based on the entire sample.
We also recorded evidence of serial killer
stalking, noting reports of intrusive or clandes-
tine pursuit, obsessive or repeated communica-
tion with a victim and/or his social contacts, and
secretive study of the victim’s routines and life-
style. As part of this, we searched for evidence
of hunting, noting deliberate and predatorial
pursuits of victims, patrolling areas where the
victim would most likely be found (e.g., cruis-
ing roads, streets, businesses), and choosing
victims based on particular characteristics, such
as hair color.
To make income comparisons between the
sexes and to the population, we consulted sev-
eral sources. The median year of first crime
committed in our sample was 1974, and there-
fore we considered U. S. Census data from 1974
(U. S. Bureau of the Census, 1976) showing that
12% of the population lived at low-income level
in 1974. However, various sources conveyed
different estimates of persons living at low-
income level in the United States over the
timespan sampled. Data from the Pew Research
Center (2015) showed that 20% of United States
households in 2015 were low-income, 71%
were middle-income, and 9% were high-
income. This represents the greatest estimate of
low income we encountered. Therefore, to be
conservative, we selected 20% as our compari-
son point.
In our analyses below, we use Cramer’s Vas
one measure of effect size. It is helpful here to
present Rea and Parker’s (2014) interpretation
of Cramer’s V. They suggested that .20 and
under denotes a weak association, .20 to .40, a
7SEX DIFFERENCES IN SERIAL KILLERS
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moderate association, .40 to .60 a relatively
strong association, and .60 and over a strong
association (p. 219). We also use Cohen’s was
a measure of effect size. Cohen (1988) noted
that .10 conveys a small, .30 conveys a medium,
and .50 a large effect size (pp. 224 –227).
Although deductive disclosure may be possi-
ble with some of our cases, in the present arti-
cle, we do not provide a list of names of the
sampled serial killers, as this is against ethical
best practice in nomothetic research. Also, it
may be the case that serial murderers committed
their crimes for fame and notoriety (see Hag-
gerty, 2009; M. A. Harrison et al., 2015;
Hickey, 2013), and we wish to avoid reinforce-
ment of such.
Results
For ease of reference, Table 1 presents an
overview of descriptive statistics of the main
findings of this study. In support of our first
hypothesis regarding victim familiarity, MSKs
(85.5%) were nearly six times more likely than
FSKs (14.5%) to kill at least one stranger,
2
(1,
N⫽110) ⫽55.31, p⬍.001, Cramer’s V⫽
.709. In contrast, FSKs (90.9%) were nearly
twice as likely as MSKs (48.1%) to kill at least
Table 1
Comparison of Serial Killers (N ⫽110) by Sex
Variable Subcategory MSK FSK
Targeted stranger — 85.5% 14.5%
Targeted someone familiar — 48.1% 90.9%
Related to victim
ⴱ
— 9.1% 58.2%
Murdered spouse/partner — 10.9% 27.3%
Sex profile of victims Only female 49.1% 13.0%
Only male 16.4% 19.6%
Both male and female 34.5% 67.4%
Age of victims Only adult victims 49.1% 49.1%
Only child victims 3.8% 27.3%
Both adults and children 47.1% 23.6%
Motive for killing Financial gain 16.7% 51.9%
Sexual 75.0% 7.3%
Stalked victim before murdering — 65.4% 3.6%
Committed murders outside of birthplace — 67.3% 25.5%
Committed murders across different U.S. states — 40.0% 18.2%
Economic class Lower 67.4% 38.1%
Middle 26.1% 57.1%
Upper 6.5% 4.8%
Education level High school or less 73.1% 46.2%
Some college or more 26.9% 53.8%
In relationship at time of crimes — 31.7% 56.6%
Reported mental health issue — 89.5% 42.6%
Method of killing Asphyxiation 47.2% 30.9%
Shooting 20.8% 9.1%
Stabbing 17.0% 5.5%
Beating/Blunt Force 7.5% 1.8%
Poisoning 7.5% 47.3%
Drowning — 3.6%
Neglect — 1.8%
Killing span, mean years (SD) — 8.69 (11.01) 7.78 (7.86)
Mean (SD) number of victims — 8.55 (6.95) 6.02 (4.93)
Judicial disposition Death Penalty 54.5% 23.6%
Prison/Jail 40% 63.6%
Nickname conveys gender — 25.0% 73.3%
Nickname conveys brutality — 78.1% 53.3%
Note. Where information was unavailable for the entire sample, we calculated the percentage based on the number of cases
for which we had data.
ⴱ
Related by blood or marriage.
8 HARRISON, HUGHES, AND GOTT
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one person familiar to them,
2
(1, N⫽109) ⫽
23.60, p⬍.001, Cramer’s V⫽.465. FSKs
(58.2%) were also far more likely than MSKs
(9.1%) to be related (by blood or marriage) to
their victims,
2
(1, N⫽110) ⫽29.69, p⬍
.001, Cramer’s V⫽.520. Of the 5 MSKs who
killed relatives, only 1 killed a blood relative,
while the remaining 4 killed wives. FSKs
(27.3%) were more than twice as likely to have
killed a spouse or long-term partner among their
victims as were MSKs (10.9%),
2
(1, N⫽
110) ⫽4.77, p⫽.029, Cramer’s V⫽.208.
In support of the second hypothesis, MSKs
(65.4%) were much more likely than FSKs
(3.6%) to engage in stalking and/or “hunting” of
their victims,
2
(1, N⫽107) ⫽45.65, p⬍
.001, Cramer’s V⫽.653. Of note, for the only
two FSKs identified as stalking their victims,
reports indicated that men were also involved in
the crimes.
In support of the third hypothesis, MSKs
(67.3%) were more likely than FSKs (25.5%) to
commit murders outside their birth state,
2
(1,
N⫽104) ⫽18.36, p⬍.001, Cramer’s V⫽
.420. In our sample of serial murderers who
committed their crimes in the United States,
14.3% of MSKs were born outside the United
States, but no FSKs (0%) were,
2
(1, N⫽
104) ⫽8.42, p⫽.004, Cramer’s V⫽.285.
Furthermore, MSKs (40%) committed killings
across multiple states more frequently than
FSKs (18.2%) did,
2
(1, N⫽110) ⫽6.35, p⫽
.012, Cramer’s V⫽.240.
To address the fourth hypotheses, we found
that MSKs were most likely to be lower class
(67.4%), while some MSKs were middle class
(26.1%) and upper class (6.5%),
2
(2, N⫽
46) ⫽26.65, p⫽⬍.01, w⫽.791. Compared
to the 20% estimate of low-income individuals
in the population (Pew Research Center, 2015),
there was a marked overrepresentation of low
income among MSKs,
2
(2, N⫽46) ⫽65.04,
p⬍.001, w⫽1.19. FSKs were mostly middle
class (57.1%) and lower class (38.1%), but were
also unlikely to be upper class (4.8%),
2
(2,
N⫽42) ⫽18.74, p⫽⬍.01. There was also an
overrepresentation of low income among FSKs
in comparison to population data,
2
(2, N⫽
42) ⫽8.85, p⫽⬍.01, w⫽.459. MSKs were
more frequently of lower income than were
FSKs,
2
(1, N ⫽88) ⫽7.75, p⫽.006, Cram-
er’s V⫽.293.
To further assess sex differences in socioeco-
nomic status, we were able to discern education
level for 52 serial killers in our sample. Reports
revealed unequal academic achievement be-
tween the sexes,
2
(1, N⫽52) ⫽3.91, p⫽
.048, Cramer’s V⫽.274. The majority of
MSKs (73.1%) earned a high school diploma or
lower (e.g., drop-out), whereas the majority of
FSKs (53.8%) attended at least some college or
earned a college or professional degree.
In support of our fifth hypothesis, MSKs
(75%) were far more likely than FSKs (7.3%) to
have a sexual motive for killing,
2
(1, N⫽
107) ⫽51.01, p⬍.001, Cramer’s V⫽.690.
FSKs (51.9%) were more likely than MSKs
(16.7%) to kill for financial gain,
2
(1, N⫽
102) ⫽13.78, p⬍.001, Cramer’s V⫽.367.
Furthermore, when examining only the serial
murderers who were in prime reproductive age
when they first killed (teens, 20s, and 30s), 80%
of MSKs had a sexual motive for killing as
compared to only 8.2% of FSKs,
2
(1, N⫽
94) ⫽49.52, p⬍.001, Cramer’s V⫽.726.
With a low sample size of those aged 40 and
older, 0 out of 6 FSKs and 3 out of 7 MSKs
(42.9%) had a sexual motive for killing. This
difference was not statistically significant.
Within our sample, MSKs had killed more
victims (M⫽8.55, SD ⫽6.95; range: 3–33)
than FSKs (M⫽6.02, SD ⫽4.93; range: 3–31),
t(97) ⫽2.20, p⫽.030, d⫽.42. Contrary to the
results of previous research, there was no dif-
ference in span of years killing (i.e., number of
years murders took place) between MSKs (M⫽
8.69, SD ⫽11.01) and FSKs (M⫽7.78, SD ⫽
7.86), t(108) ⫽.497, p⫽.621.
When considering the sex of the targeted
victims, MSKs most commonly killed female
victims only (49.1%), followed by both male
and female victims (34.5%), and male victims
only (16.4%). This distribution differed from
that of FSKs, who most commonly killed both
males and females (67.4%), followed by males
only (19.6%), and females only (13%),
2
(1,
N⫽101) ⫽15.57, p⬍.001, Cramer’s V⫽
.393.
It was difficult to determine exact victim age,
as generalizations were frequently reported, for
example, “all victims were elderly.” In some
instances, reports indicated that body decompo-
sition rendered exact age identification impos-
sible. We were able to discern the targeted ages
of the victims for 108 serial murderers and
9SEX DIFFERENCES IN SERIAL KILLERS
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classified the serial killer victims into three
groups: adult victims only, child victims only,
and a combination of both adult and child vic-
tims. FSKs were more likely to target only
adults (49.1%) than the categories of only chil-
dren (27.3%) and both adults and children
(23.6%),
2
(2, N⫽56) ⫽7.11, p⫽.029, w⫽
.356. MSKs targeted adults only (49.1%) and
both adults and children (47.1%), but were very
unlikely to target only children (3.8%),
2
(2,
N⫽53) ⫽20.87, p⬍.001, w⫽.628. Further-
more, MSKs (3.8) were significantly less likely
to kill children only, compared to FSKs
(27.3%),
2
(1, N⫽108) ⫽11.24, p⫽.001,
Cramer’s V⫽.323.
Most MSKs (68.3%) were not in a relation-
ship (i.e., single, divorced, or widowed) at the
time of the crimes, but most FSKs (56.6%) were
in a relationship (i.e., married or long-term part-
ner) at the time of their crimes. These results
reflect an unequal sex distribution,
2
(1, N⫽
94) ⫽5.77, p⫽.016, Cramer’s V⫽.248.
Out of the 73 serial killers for which we
found mental health information (mentioned di-
agnosis, or confirmation of no history of mental
illness), 54.8% had documented issues. Among
MSKs, 17 out of 19 (89.5%), and among FSKs,
23 out of 54 (42.6%) were reported to be men-
tally ill at the time of crimes; this reflected a sex
difference,
2
(1, N⫽73) ⫽12.47, p⬍.001,
Cramer’s V⫽.413.
The most common method of killing for
MSKs was asphyxiation (47.2%), followed by
shooting (20.8%), stabbing (17%), beating/
blunt force (7.5%), poisoning (7.5%),
2
(4, N⫽
53) ⫽28.04, p⬍.001, w⫽.727. For FSKs,
poisoning was the most common method
(47.3%), followed by asphyxiation (30.9%),
shooting (9.1%), stabbing (5.5%), drowning
(3.6%), beating/blunt force (1.8%), and neglect
(1.8%),
2
(6, N⫽55) ⫽72.91, p⬍.001, w⫽
1.15. These distributions were different for
MSKs and FSKs,
2
(6, N⫽108) ⫽27.68, p⬍
.001, Cramer’s V⫽.506.
Analyses revealed sex differences in disposi-
tion (end result),
2
(7, N⫽110) ⫽14.69, p⫽
.040, Cramer’s V⫽.365, whereby 54.5% of
MSKs received a death penalty for their crimes,
compared to 23.6% of FSKs. Among FSKs,
63.6% went to prison or jail (not counting death
row), compared to 40% of MSKs. Only a few
serial murderers were placed in a mental health
care facility (n⫽3 FSKs; n⫽1 MSK). One
MSK escaped; 1 MSK and 1 FSK completed
suicide; 1 FSK was placed under house arrest;
and 2 FSKs were never caught (i.e., law en-
forcement was certain of their identity, but the
FSKs remained at large).
There was no statistical sex difference in
frequency of crimes committed across U. S.
regions (U. S. Census Bureau, 2015) divided by
West (MSKs: 20%, FSKs: 10.7%); Midwest
(MSKs: 16.4%, FSKs 20%); Northeast (MSKs:
16.4%, FSKs: 18.2%); South (MSKs: 23.6%,
FSKs: 41.8%); and mixed across regions
(MSKs: 23.6%; FSKs: 9.1%),
2
(4, N⫽110) ⫽
8.06, p⫽.090. When collapsing data across
sex, most serial killers targeted victims specif-
ically in the U.S. South compared to other re-
gions (32.7%),
2
(4, N⫽110) ⫽11.36, p⫽
.023, w ⫽321. Furthermore, we considered that
some serial killers committed crimes across two
or more U. S. regions and found that 41.2% of
all serial murderers documented in this study
(45.5% of FSKs and 38.2% of MSKs) commit-
ted at least some of their murders in the South.
In cases where we found that a serial killer
was ascribed a nickname by law enforcement,
the media, or the public (n⫽47), FSK nick-
names (e.g., “Jolly Jane,” “Tiger Woman”,
“Death Row Granny”) more frequently (73.3%)
conveyed the gender of the murderer than had
MSK nicknames (25%),
2
(1, N⫽47) ⫽9.91,
p⫽.002, Cramer’s V⫽.459. In contrast,
nicknames conveying the brutality of the mur-
ders (e.g., “The Kansas City Strangler,” “The
Serial Slasher,” “The Tourniquet Killer”) were
frequently ascribed to MSKs (78.1%) compared
to those for FSKs (53.3%), but this was not a
statistically significant association,
2
(1, N⫽
47) ⫽3.00, p⫽.083.
Discussion
It is interesting to consider that men and
women committing crimes with the same des-
ignation, “serial murder,” show different moti-
vations and approaches for these murderous en-
gagements. All of our hypotheses regarding sex
differences in these murderers and their crimes
were supported, promoting our hunter-gatherer
model of serial killing. Compared to female
serial killers, male serial killers stalked and
“hunted” victims more frequently. The over-
whelming majority of MSKs targeted persons
previously unknown to them. Men’s patterns of
10 HARRISON, HUGHES, AND GOTT
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killing were more disbursed across states, and
men, more frequently than women, killed out-
side their birthplace, reminiscent of the geo-
graphic dispersion needed for hunting and for-
aging tactics. We found that only two FSKs
engaged in similar stalking behaviors; however,
men were reported to be involved in those
crimes. In contrast, female serial killers tended
to figuratively “gather” their victims, remaining
in the same areas to kill. Almost all FSKs killed
those whom they knew—those who were
around them and familiar to them. FSKs were
more likely to kill a spouse or long-term partner
and were 6 times more likely than MSKs to kill
relatives. Only one MSK was reported to kill a
blood relative.
We found that MSKs were more than 10
times as likely as FSKs to have a sexual motive
to commit serial murder and targeted mainly
adult, opposite-sex victims, rarely targeting just
children. In particular, MSKs in their prime
reproductive years (Harris, Fronczak, Roth, &
Meacham, 2011) were nearly twice as likely as
older MSKs to have a sexual motive for killing.
Previous researchers have noted that the sexual
predation exhibited by MSKs is like a hunt
(Miller, 2012). It appears that MSKs are engag-
ing in an aberrant form of mate-seeking. Of
course, killing a victim with whom one has had
sex precludes the passing on of genes; however,
we argue that the pursuit of the victim follows
evolved tendencies. On the other hand, FSKs
were 3 times as likely as MSKs to kill for
profit/resources. In line with the “gatherer” hy-
pothesis, female serial killers seem to be gath-
ering resources as a result of their killings. As
suggested by M. A. Harrison and colleagues
(2015), these findings also reflect sex-specific
fitness maximization tendencies reflective of re-
productive potential. In the ancestral environ-
ment, men with virtually unlimited sperm
would have maximized fitness chances by seek-
ing more mates, whereas women with a finite
reproductive potential would have maximized
fitness chances by securing resources for her
and her offspring (Trivers, 1972).
Male serial killers evinced characteristics of
men who are typically classified as having a low
mate value. First, MSKs overrepresented hav-
ing low income compared to the population—
results very similar to those of Stone (2001)—
and more frequently than did FSKs. There was
also a greater number of MSKs compared to
FSKs with low academic achievement. This is
consistent with the Federal Bureau of Investi-
gation’s (2005) assertion that, despite some me-
dia portrayals to the contrary, not all serial
killers are “evil geniuses.” In addition, there
were more MSKs than FSKs who were unin-
volved in a current relationship at the time of
killings, and more with reported mental illness.
Along these lines, when collapsing data across
sex, more serial murderers were committed in
the highest poverty area of the United States.
Although not an a priori consideration for
comparison of sex differences, we believed it
prudent to note the prevalence of mental illness
reports in our sample of serial killers, as we are
arguing that serial murder is a pathological vari-
ation of fitness maximization strategies for men
and for women. Serial killing often involves
prolonged torture (Miller, 2014), and our data
confirmed that the most common methods of
killing within our sample (i.e., asphyxiation by
MSKs and poisoning by FSKs) involved some
torment and suffering of victims. Many re-
searchers suggest that psychopathic personality
is prevalent in serial killers (Beasley, 2004;
Myers, Gooch, & Meloy, 2005). We urge men-
tal health and legal professionals to consider
this phenomenon in developing prevention and
treatment for violent offenders. Likewise,
Brüne (2003) and others have stressed the po-
tential contributions of evolutionary theory to
understanding mental illness. Our closest phy-
logenetic relatives, nonhuman apes, also show
evidence of abnormal symptoms commensurate
with mental health issues seen in humans such
as heightened violence and aggression, depres-
sion, anxiety, deliberate self-harm, eating disor-
ders, and even psychopathy (Brüne, Brüne-
Cohrs, McGrew, & Preuschoft, 2006; see
Shackelford & Zeigler-Hill, 2017). These ab-
normal manifestations interfere with an ani-
mal’s social integration and thus pose a threat to
survival and fitness (Brüne et al., 2006). With
this in mind, it would be beneficial to study
murder and serial murderers further through
comparative and evolutionary models of psy-
chopathology (Fábrega, 2002).
We noted that the noms de guerre of FSKs
tended to emphasize the gender of the perpetra-
tor compared to those ascribed to MSKs. Fur-
thermore, although not statistically significant,
it is arguably meaningful that over three quar-
ters of men had nicknames that underscored
11SEX DIFFERENCES IN SERIAL KILLERS
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their gruesome modi operandi (e.g., “The Bind,
Torture, Kill Strangler”), versus slightly more
than half of FSKs’ nicknames. Because the in-
cidence of reported FSKs is lower than that of
MSKs (Hickey, 2010), perhaps law enforce-
ment or the media feel compelled to highlight
FSKs’ gender when describing these cases. It
may also be the case that people view the crimes
of women as less severe even when the outcome
is the same. As such, among our sample of
serial killers, there were proportionally far
fewer FSKs than MSKs who were sentenced to
capital punishment. In one example, a newspa-
per story covering the trial of a suspected fe-
male serial killer reported in its first paragraph
that she was “probably the prettiest defendant
ever tried for murder” in that city (“KC Mur-
deress on Trial,” 1961). The defendant was later
acquitted and was photographed giving auto-
graphs to the jury (“Too Many Loopholes,”
1961).
Some caveats are in order when interpreting
this work. There are established works that
speak to MSK and FSK motives and crimes,
evincing different profiles. However, the pres-
ent study is the only research known to us that
collected data and directly, statistically com-
pared the motivations and behaviors of MSKs
and FSKs. Additionally, in the present article
we do not attempt to explain all subtypes of
MSKs or FSKs, nor do we promote evolution-
ary psychological perspective as explaining all
aspects of serial murder. Also, theorists note
that hunter-gather behaviors were multidimen-
sional in terms of predation, mobility, use of
technology, and use of resources (Ames &
Maschner, 2000; Chatters, 1987), so broad-
strokes portraits of ancestral tendencies may not
suffice. Furthermore, our data describe known
serial killer behaviors and crimes. There may be
a different profile of traits and crimes for those
whose identities have never been determined.
Although popular in media reports and public
interest, serial murder is a rare phenomenon.
One forensic coroner and investigator estimated
the chance of being murdered in North America
by a serial killer is about .0004% (Rodgers,
2015). When comparing serial murder against
the odds of preventable deaths, one is more
likely to die from drowning or being hit by a
motor vehicle (National Safety Council, 2017).
Thus, obtaining reports on serial murderers
yielded a relatively low sample size, which
made statistical analyses challenging in some
regards; nonetheless, the appreciable effect
sizes found in this investigation strongly sup-
port sex differences.
In addition, there are marked limitations to
examining media reports for psychological data
(Farrell et al., 2013; M. A. Harrison & Bowers,
2010; M. A. Harrison et al., 2015; Keeney &
Heide, 1994), where we had to contend with any
biases presented in the reports. What is reported
in the media may be sensationalized in the in-
terest of a “good story,” and thus we endeav-
ored to verify claims with more than one source
where possible. Furthermore, we collected re-
ports dating back to the 1800s, but it may be the
case that increasingly sophisticated investiga-
tive and reporting techniques over time changed
the depth, breadth, or accuracy of media report-
ing. We documented information available to
us, but we stress that missing information does
not convey the absence of a trait or behavior.
Absence of information could have created un-
derestimates of the frequency of some of the
traits and behaviors we documented. An exam-
ple of unavailable yet important evidence would
be the exact number of children each serial
murderer had; this would have allowed us to
examine the reproductive fitness of serial killers
from an evolutionary perspective. Thus, we
urge caution when interpreting these data and
encourage continued investigation regarding
these phenomena.
In conclusion, research directly comparing
data on FSKs and MSKs within one study is
uncommon. Thus, our data were among the first
that yielded marked differences in the charac-
teristics and crimes of female and male serial
murderers through a direct comparison. We
demonstrated that evolutionary and compara-
tive psychological perspectives may further in-
form our understanding of murder and serial
murder. To augment efforts at understanding
and preventing these crimes, future researchers
and law enforcement officials may wish to keep
this in mind. We stress, however, that while we
have interpreted the data utilizing evolutionary
theory by suggesting that some of the methods
and motives of these vicious crimes may be a
byproduct of unconscious drives, we are cer-
tainly not excusing these crimes under an um-
brella of genetic predisposition. There is also a
likely cluster of proximate variables (e.g., de-
velopmental milieu, economic stress, personal-
12 HARRISON, HUGHES, AND GOTT
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ity, hormones, neurological functioning) one
must consider in deciphering the mysteries of
serial killing.
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Received August 12, 2018
Revision received November 11, 2018
Accepted November 14, 2018 䡲
16 HARRISON, HUGHES, AND GOTT
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