The Challenges of Keeping an Intimate Relationship: An Evolutionary Examination

Abstract

Keeping an intimate relationship is challenging, and many people face difficulties in doing so. In the current research, we have attempted to identify these difficulties, within the context of an evolutionary theoretical framework. More specifically, by using a combination of qualitative research methods in a sample of 163 Greek-speaking participants, we identified 78 such difficulties. By employing maximum likelihood analysis on the scores of 1,099 Greek-speaking participants, we classified these difficulties in 12 broader factors. The most important factor was "Fading away enthusiasm," followed by "Long work hours" and "Lack of personal time and space." Almost 70% of the participants indicated that at least one factor, and 41% indicated that three or more factors caused them difficulties. Significant sex effects were found for most factors, indicating that men and women differed in the importance they ascribed to these difficulties. Moreover, significant age, marital status and number of children effects were found for several factors.

Full text

Original Article
The Challenges of Keeping an Intimate
Relationship: An Evolutionary Examination
Menelaos Apostolou
1
and Yan Wang
2
Abstract
Keeping an intimate relationship is challenging, and many people face difficulties in doing so. In the current research, we have
attempted to identify these difficulties, within the context of an evolutionary theoretical framework. More specifically, by using a
combination of qualitative research methods in a sample of 163 Greek-speaking participants, we identified 78 such difficulties. By
employing maximum likelihood analysis on the scores of 1,099 Greek-speaking participants, we classified these difficulties in
12 broader factors. The most important factor was “Fading away enthusiasm,” followed by “Long work hours” and “Lack of
personal time and space.” Almost 70% of the participants indicated that at least one factor, and 41% indicated that three or more
factors caused them difficulties. Significant sex effects were found for most factors, indicating that men and women differed in the
importance they ascribed to these difficulties. Moreover, significant age, marital status and number of children effects were found
for several factors.
Keywords
difficulties in keeping an intimate relationship, keeping an intimate relationship, mating, mismatch problem, intimate relationships
Date received: February 13, 2020. Revision Submitted: July 30, 2020; Accepted: July 31, 2020
Introduction
Maintaining an intimate relationship is challenging. Across
different societies, divorce has become increasingly common;
for instance, in Western societies, it has been estimated that one
in two marriages would end up in divorce (Cherlin, 2009; Raley
& Bumpass, 2003; Schoen & Standish, 2001). Recent studies in
the Greek cultural context have found that about one in three
adult people experienced difficulties in keeping an intimate
relationship (Apostolou et al., 2018), which can also potentially
explain why a large proportion of the population does not have
an intimate partner (Apostolou, Papadopoulou, & Georgiadou,
2019). The present study aims to identify the difficulties people
face in keeping an intimate relationship, to classify them in
broader categories, to assess their importance, and to examine
some of their contingencies.
Current Literature
We were not able to locate any study that has attempted to
examine the difficulties people face in maintaining an intimate
relationship. The most relevant literature has to do with the
reasons for getting a divorce. In particular, the difficulties in
keeping an intimate relationship are likely to lead to the termi-
nation of a relationship, which means that this literature could
provide us with insights about the difficulties in maintaining a
relationship. Studies have found that predictors of marital dis-
solution included domestic violence, conflict, infidelity, a weak
commitment to marriage, and low levels of love and trust
between spouses (Clements et al., 2004; DeMaris, 2000;
Gottman & Levenson, 2000; Kurdek, 2002; Lawrence & Brad-
bury, 2001; Orbuch et al., 2002).
In more detail, Bloom and colleagues (1985) employed a
sample of 153 newly separated but not yet divorced individuals
in the United States, and found that the most common sources
of marital dissatisfaction were communication difficulties,
value conflicts and boredom, while physical abuse, drinking
and drug abuse were the least common sources. Amato and
1
Department of Social Sciences, University of Nicosia, Cyprus
2
Fudan University, Shanghai, China
Corresponding Author:
Menelaos Apostolou, University of Nicosia, Department of Social Sciences, 46
Makedonitissas Ave., Nicosia 1700, Cyprus.
Email: m.apostolou@gmail.com
Evolutionary Psychology
July-September 2020: 1–11
ªThe Author(s) 2020
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DOI: 10.1177/1474704920953526
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(https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission
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Previti (2003), analyzed the interviews of 208 divorced indi-
viduals in the United States, and found that infidelity was the
most commonly reported cause, followed by incompatibility,
drinking or drug use, and growing apart. Another study
employed a sample of 886 divorcing parents in the United
States, and found that the most common reasons for divorce,
cited by both men and women, were growing apart, communi-
cation problems, and not enough attention from the spouse
(Hawkins et al., 2012). They found also that, infidelity was
given as an important reason for divorce by slightly more than
one third of respondents. A more recent study employed a
sample of 515 Greek-speaking participants, and found that
being an abusive spouse was the most important factor for
divorce, followed by incompatibility and in-law problems
(Apostolou, Constantinou, & Anagnostopoulos, 2019).
The literature on the reasons which could lead to divorce is
insightful for understanding the difficulties that people face in
maintaining an intimate relationship. For instance, it indicates
that a common such reason is infidelity, which suggests that a
taste for sexual variation, accompanied by a lack of restraint, is
one possible difficulty in keeping an intimate relationship. Still,
this literature is far from adequate, as there may be many dif-
ficulties in maintaining an intimate relationship, which may not
be serious enough to lead to the dissolution of marriage, and
thus, are not captured by the literature on divorce. Accordingly,
research in required to study specifically the difficulties that
people face in keeping an intimate relationship. These difficul-
ties could be better understood within the context of an evolu-
tionary theoretical framework that will be discussed next.
Why People Face Difficulties in Keeping
an Intimate Relationship
Conflict Between the Sexes
In an evolutionary perspective, human behavior arises from
brain mechanisms or adaptations that have evolved to enable
the propagation of genes that code for them to future genera-
tions. Thus, in a general sense, people are understood to behave
in a way that enables them to increase the representation of the
genes they carry to future generations, usually called fitness
(Tooby & Cosmides, 2015). The main way to achieve this goal
is to have children who carry their parents’ genetic material to
the next generation, and in sexually reproducing species like
our own, doing so demands gaining access to the reproductive
capacity of the opposite sex. In addition, children require con-
siderable parental investment in order to reach sexual maturity
and become independent from their parents. Therefore, gaining
access to the reproductive capacity of the opposite sex is usu-
ally not sufficient for ensuring that one’s genetic material will
pass successfully to the next generation. What is required for
this endeavor to be successful is establishing a context where
two parents consistently divert investment to their children.
The fitness benefits from such arrangement translate into selec-
tion pressures for mechanisms to evolve that would make
establishing and keeping an intimate relationship possible. For
instance, emotions such as romantic love and jealousy are
adaptations which enable people to attract and retain partners
(Buss, 2017b). This theoretical perspective explains why most
people strive to establish and keep an intimate relationship, and
could also explain why many people frequently face difficulties
in doing so.
More specifically, common reproductive benefits motivate
individuals to come together and to keep a relationship for
some time. This endeavor would be smooth if the two parties
had only common reproductive interests. Yet, by being geneti-
cally different, the two parties have also diverging interests,
which means that one party could increase its reproductive
success at the expense of the other party. For instance, one
party may employ a mating strategy that increases its fitness
at the expense of the other party.
In more detail, men’s and women’s approach toward mating
can be seen as strategic, in the sense that people follow a
strategy when engaging in mating that enables them to increase
their reproductive success (Buss & Schmitt, 1993). Three such
strategies could be identified: A short-term mating strategy
involves engaging in many casual relationships and investing
little in any offspring that may come from them, while a
long-term mating strategy involves establishing few intimate
relationships, and investing heavily in any offspring that come
from them (Buss & Schmitt, 1993, 2019). Both strategies have
advantages and disadvantages. For instance, a short-term mat-
ing strategy could enable a woman to secure help and assis-
tance from several different men, but she would face the risk of
raising a child on her own. A long-term mating strategy would
enable a man to have children who receive adequate support
from both parents, but he would forgo the opportunity to gain
sexual access to other women. A mixed strategy involves peo-
ple entering in long-term relationships but have parallel casual
relationships, which could potentially enable men and women
to receive the benefits of both the long- and short-term strategy,
without paying their costs (Buss & Schmitt, 1993). For
instance, a man who adopts such strategy could establish a
family and have children who receive long-term investment
from both parents, but at the same time, exploit opportunities
for gaining sexual access to different women. It needs to be said
that these strategies are not conscious, in the sense that people
choose to adopt one or the other. The fitness benefits of these
strategies have selected for adaptations that would enable peo-
ple to adopt them. For example, individuals would not feel
sexually satisfied with one partner that would motivate them
to adopt a short-term mating strategy.
The adoption of a mixed strategy by one partner conflicts
with the interests of the other, causing difficulties in keeping a
relationship. More specifically, men can remain in a long-term
relationship, but exploit any opportunities for extra-pair sex.
This strategy is not to the best interest of their partners, who
risk losing investment to other women and their children, con-
tracting a sexual transmitted disease, losing their partners to
another woman and so on. In a similar vein, women can gain
resources such as gifts by engaging in extra-pair sex, a strategy
which is not to the best interests of their partners, who risk
2Evolutionary Psychology

raising other men’s children, losing their partners to other men,
contracting a sexual transmitted disease and so on.
Extra-pair mating is only one area where the conflict
between the sexes is materialized (see Buss, 2017a, for a more
inclusive discussion of the topic). It constitutes a good example
however, of the argument that keeping an intimate relationship
is inherently difficult because the parties involved have con-
flicting interests. On this basis, it is predicted that many of the
reasons which caused difficulties to people in keeping an inti-
mate relationships, would reflect conflicting interests between
parties.
Adoption of a Short-Term Mating Strategy
The adoption of a short-term mating strategy, could prevent
people from keeping an intimate relationship. More specifi-
cally, several individuals may adopt a short-term mating strat-
egy; having however, a long-term intimate relationship would
interfere with this strategy, as it would prevent people from
having different partners. Thus, their behavioral mechanisms
may have evolved to prevent the formation of long-term rela-
tionships: People may have an intense desire for sexual variety
accompanied by high libido, they may not fall in love or they
may have feelings which quickly reside following sexual inter-
course. On this basis, we predict that several of the reasons
which caused difficulties to people in keeping an intimate rela-
tionship would reflect the adoption of a short-term mating
strategy.
Mismatch Problem
As discussed above, converging interests over mating have led
to the evolution of mechanisms that enable people to keep an
intimate relationship. Nevertheless, these, as all other adapta-
tions, have been shaped in ancestral human societies, and may
not work well in contemporary ones (Tooby & Cosmides,
2015). This is likely to be the case if the contemporary condi-
tions in which mating takes place are considerably different
from ancestral human conditions, and the transition was rela-
tively recent for selection forces to have sufficient time to
adjust these adaptations to the demands of the modern environ-
ment. This is known as the mismatch problem (Crawford,
1998; Li et al., 2018; Maner & Kenrick, 2010), and it is likely
to be at play in causing people difficulties in keeping a
relationship.
More specifically, there are reasons to believe that the envi-
ronment in which mating takes place has experienced consid-
erable changes very recently in the evolutionary timescale. In
more detail, anthropological, historical and phylogenetic evi-
dence indicates that in ancestral human societies mate choice
was typically regulated, with parents arranging marriages for
their children (Apostolou, 2014; Walker et al., 2011). In addi-
tion, anthropological, historical and physiological evidence
indicates that in ancestral human societies, male-male compe-
tition, where men form alliances in order to monopolize by
force the women of other men, was also strong (Puts, 2010,
2016). Anthropological and historical evidence indicates
further that, in ancestral human societies, our ancestors had
also space to exercise mate choice, usually through divorce
or extra-pair relationships (Apostolou, 2017a).
The transition that followed the industrial revolution in the
18th century has given rise to post-industrial societies where
mate choice is not regulated or forced, but it is freely exercised.
This transition had occurred very recently for selection forces
to have sufficient time to adjust the adaptations related to keep-
ing an intimate relationship to the demands of the modern
context. Accordingly, people carry adaptations that may have
worked effectively in the ancestral environment, but may be
less effective in enabling people to keep a relationship in the
current environment. In more detail, one important difference
between ancestral pre-industrial societies and contemporary
post-industrial ones is that the former were lacking social sup-
port and protection systems. In particular, when misfortune
happens, in most post-industrial societies people can rely on
social structures such as free health care system, unemploy-
ment benefits, food coupons etc. which was not the case in
ancestral pre-industrial societies, where people had to rely on
their families to deal with such misfortunes. Similarly, as there
were no civil protection systems such as the police, people had
also to rely on their families for protection from internal and
external threats. Furthermore, in contemporary post-industrial
societies, people gain their subsistence by working outside their
family, while in in ancestral pre-industrial societies, the family
was the main unit of production. For instance, the family mem-
bers would cultivate its land and herd its animals, which was
the primary way for them to gain subsistence. Accordingly, in
an ancestral context, the formation of a family was not only a
way to have children, but it was necessary for subsistence,
protection and support in case of misfortune.
These factors would have provided a strong incentive to our
ancestors to keep their intimate relationships, overlooking sev-
eral of their partners’ faults. For example, people would be
reluctant to end a relationship that could lead to children, and
would enable them to gain their subsistence because their part-
ners lacked say a pleasant personality or were not always faith-
ful. That is, the benefits of an intimate relationship in the
pre-industrial context exceed considerably the costs of not hav-
ing a pleasant personality and be at times unfaithful.
In contemporary post-industrial societies, the
non-reproductive benefits of having a family have been largely
gone away: People can rely on the well-developed social pro-
tection systems rather on their partners and other family mem-
bers in case misfortune finds them, are protected by the police
and the army and not by their partners, while they gain their
subsistence by selling their labor outside their family unit.
Therefore, the benefits of being in a relationship in order to
receive help with the subsistence effort and protection, have
considerable diminished in the contemporary context, and do
not balance the costs of traits such as being unpleasant to be
with and not always faithful. Accordingly, people would be less
willing to overlook such faults, meaning that those who have
Apostolou and Wang 3

them would experience difficulties in keeping an intimate
relationship.
In effect, strong selection pressures are exercised on these
traits to adjust them to modern conditions: For instance, people
would become more easygoing, which would make them more
effective in keeping an intimate relationship. Nevertheless, the
transition to post-industrialism has been very recent in evolu-
tionary terms, meaning that such selection pressures have not
yet materialized in shaping these adaptations to deal with the
modern conditions. In effect, there should be several people
today who have traits that make them difficult to be accepted as
partners, and who would thus, face difficulties in keeping an
intimate relationship.
Sex Differences
Due to biological differences arising from different evolution-
ary specializations, men’s reproductive success is positively
related to the number of opposite-sex partners they can have
sexual access to, which is not the case for women (Buss &
Schmitt, 1993, 2019). For example, a man can produce 100
offspring by mating with 100 fertile women over the course
of a year, whereas a monogamous man, similarly to a mono-
gamous or a polygamous woman, would be able to sire only
one child with his partner during that time.
This difference translates into selection pressures for beha-
vioral mechanism to evolve, turning men more likely to adopt a
short-term or a mixed strategy (Buss & Schmitt, 1993, 2019).
As discussed above, the adoption of these strategies is likely to
cause difficulties to people in keeping an intimate relationship.
On this basis, we predict that a sex-difference would arise, with
men facing more difficulties than women in keeping an inti-
mate relationship due to reason associated with the adoption of
a short-term or a mixed mating strategy.
Study 1
The purpose of this study was to identify the difficulties that
people faced in keeping a romantic relationship.
Method
Participants
The research took place in a medium-sized private University
in the Republic of Cyprus. Participation was voluntary, and
people were required to be at least 18 years old in order to
participate. Participants were recruited through an advertise-
ment that was placed on Facebook. We advertised that we were
looking for people who were experienced in intimate relation-
ships. There were two groups of participants, a group respond-
ing to interviews and a group responding to open-ended
questionnaires. With respect to the in-depth interviews,
40 Greek-speaking participants took part (20 women, 20 men).
The mean age of women was 34.3 (SD ¼7.4), and the mean
age of men was 36.6 (SD ¼7.1). Moreover, 44.2%of the
participants were married, 26.2%were in a relationship,
15.2%were single and 14.4%were divorced. With respect to
the open-ended questionnaires, 123 Greek-speaking partici-
pants took part (63 women, 60 men). The mean age of women
was 30.5 (SD ¼8.4), and the mean age of men was 32.1 (SD ¼
8.9). Furthermore, 31.3%of the participants were married,
28.2%were in a relationship, 25.6%were single and 14.8%
were divorced.
Materials
In-depth interviews. In order to identify the different reasons that
caused people difficulties in keeping an intimate relationship, a
series of semi-structured interviews were conducted. The inter-
views took place in a psychology laboratory located at the
University premises, and lasted 40 minutes on average. The
interviews were conducted by one of the authors and one inde-
pendent graduate student. Participants signed a consent form,
and subsequently, they filled in their demographic details (i.e.,
sex, age, marital status).
Participants were asked to discuss the different difficulties
they faced in keeping an intimate relationship. We employed
follow-up and probing questions in order to get more detailed
information on specific reasons. Participants’ responses were
recorded on paper. Following the conclusion of the interview,
participants were debriefed and thanked.
Open-ended questionnaires. The open-ended survey had two
parts. In the first part, participants were asked to indicate as
many reasons as they could, which caused them difficulties in
keeping an intimate relationship. In the second part, demo-
graphic information was collected (i.e., sex, age, marital status).
Results
In order to analyze the data from the in-depth interviews and
the open-ended questionnaires, the following procedure was
adopted: Two independent graduate students were employed,
a man and a woman, who coded and categorized responses to
supraordinate categories. Similar responses were added to the
supraordinate category, and when a dissimilar response arose, a
new supraordinate category was created. Answers that con-
tained multiple reasons were eliminated, as they were difficult
to interpret. In addition, reasons with unclear or vague wording
were also eliminated. After processing about 25%of the
responses, the data for each coder were compared. The coders
agreed to most of the supraordinate categories. For a few cases
where there was not complete overlap, one of the authors was
consulted and eventually agreement was reached for 100%of
the supraordinate categories. Subsequently, coders proceeded
to code the remaining responses. Overall, 78 difficulties in
keeping an intimate relationship were identified.
Study 2
The purpose of this study was to classify the reasons identified
in Study 1 to broader categories of reasons which caused dif-
ficulties to people in keeping an intimate relationship.
4Evolutionary Psychology

Methods
Participants
Four research assistants were employed for the purpose of
this study. They recruited individuals who volunteered to take
part in a research on romantic relationships (no payment was
given). Prospective participants had to be adults (18 years old
or older) in order to participate. The research took place in
Greece and in the Republic of Cyprus, and the data collection
process lasted 4 months. The participants were initially asked
to sign a consent form, and subsequently they were given the
survey. After completing the survey, they put the question-
naire in an unmarked envelope and sealed it. In total, 1,099
Greek-speaking participants took part (592 women, 507
men). The mean age of women was 32.7 (SD ¼11.9) and
the mean age of men was 33.5 (SD ¼10.6). Moreover,
34.7%of the participants were married, 30.8%were single,
27.1%were in a relationship, 6.7%were divorced and 0.7%
were widowed. Finally, participants had a mean of 0.81 (SD
¼1.17) children.
Materials
The survey had two parts. In the first part, participants were
asked to indicate their agreement on how each of the 78 items
identified in Study 1 were likely to cause them difficulties in
keeping an intimate relationship. Participants’ answers were
recorded in a 5-point Likert scale: 1-strongly disagree,
5-strongly agree. Finally, in the second part, demographic
information was collected (sex, age, marital status, number of
children).
Results
Factor Structure
In order to classify the 78 reasons into broader factors, we
employed maximum likelihood analysis using the direct obli-
min as the rotation method. The KMO statistic indicated that
our sample was very good for principal components analysis to
be performed (KMO ¼.97). On the basis of the Kaiser criterion
(Eigenvalue > 1), 12 factors have been extracted, and are pre-
sented in Table 1. Note that, we did not include any items with
a factor loading below .300 (see Field, 2018). In addition, the
“Frequently, I do not behave well to my partner” item loaded to
the “Lack of effort factor” (.381) but also to the “Behavioral
issues” factor (.305). The “I often break out on my partner”
loaded to the “Character issues” factor (.332) and to the
“Behavioral issues” factor (.301). Finally, the “I feel that a
relationship constrains me” item loaded to the “Lack of per-
sonal time and space” factor (.413), and to the “Clinginess”
factor (.361). We classified the items to the factors for which
they had higher loading. The internal consistency of the
extracted factors (a) ranged from .94 to .68 with a mean of
.82. Furthermore, we created 12 new variables by summing the
scores of the difficulties composing each factor and dividing by
their number. We subsequently performed maximum likeli-
hood analysis on these variables. The results indicated only
one extracted domain, suggesting that the extracted factors
could not be classify to broader domains. Finally, we per-
formed Pearson’s product moment correlation on the 12 vari-
ables and the results are presented in Table A in the Appendix.
The first factor that emerged was the “Lack of effort,”
where people did not make enough effort for the relation-
ship to work, did not look after their partners’ needs, lost
interest in their partners, and became distant from them. In
the “Bad sex” which followed next, participants indicated
that bad sex, disagreement with their partners about inter-
course frequency, and sexual incompatibility, caused them
difficulties in keeping a relationship. In the “Behavioral
issues,” participants indicated that being aggressive, having
psychological problems and addictions prevented them from
keeping an intimate relationship. Moreover, in the
“Character issues,” participants indicated that being quirky,
selfish and insecure constrained them from keeping a rela-
tionship. In the “Fading away enthusiasm,” enthusiasm and
feelings of romantic love fading away quickly, made the
continuation of the relationship difficult. “Children” also
placed strain on the relationship, as they absorbed consid-
erable time and energy from both partners.
Furthermore, in the “Social circle issues,” strain on the
relationship emerged from partners not having good rela-
tionships with each other’s family and friends. In the “Lack
of personal time and space,” people felt that they needed
more personal time and space, and that their partners were
oppressing them and were clingy. The “Clinginess” was the
other side of this coin, with people becoming
over-dependent and clingy on their partners, which presum-
ably made keeping the relationship difficult. In the
“Infidelity and abuse” which followed next, partners’ infi-
delities and physically abusive behavior caused difficulties
to people in keeping a relationship. In the “Not being mono-
gamous,” people indicated that they were not monogamous,
and they wanted to have experiences with other partners, so
being in an exclusive intimate relationship constrained
them. Finally, in the “Long work hours,” people focused
on their careers, so there was limited time left to invest in
their relationship.
In order to get an estimate of importance, we placed the
mean scores of each extracted factor in a hierarchical order.
As we can see from Table 2, the highest mean was for the
“Fading away enthusiasm,” followed by the “Long work
hours” and the “Lack of personal time and space.” At the
bottom of the hierarchy were the “Behavioral issues,” the
“Social circle issues” and the “Not monogamous.” The stan-
dard deviations indicated that there was substantial variation
in the scores for each factor. Thus, in order to get a more
accurate understanding of how many participants indicated
above average scores for each factor, we calculated the num-
ber of participants who gave above the mid of the scale
scores (i.e., >3). As we can see from Table 2, the highest
percentage was for the “Fading away enthusiasm,” followed
Apostolou and Wang 5

by the “Lack of personal time and space” and the “Long
work hours.” The lowest percentages were for the
“Behavioral issues,” the “Not monogamous” and the “Lack
of effort.” Finally, we calculated how many participants indi-
cated difficulties in more than one factors. We found that
30.9%did not give a mean score above “3” in any of the
factors, meaning that 69.1%indicated an above “3” difficulty
in at least one factor. More specifically, 16.8%indicated
difficulty in one factor, 11.3%in two factors, 10.1%in three
factors, 7.1%in four factors, and 23.8%in five or more
factors.
Significant Sex, Age, Marital Status and
Number Of Children Effects
In order to identify significant effects, we performed a series of
MANCOVAs. More specifically, we entered the items
Table 1. The Extracted Factors and the Respective Factor Loadings in
Study 2.
Factors
Factor
loadings
Lack of effort
I do not take into consideration my partner’s needs .577
I find it difficult to understand my partner’s needs .562
I find it difficult to tolerate my partner’s idiosyncrasies .538
I do not make enough effort for the relationship
work
.509
I neglect my partner .493
My interest for my partner soon fades away .485
I become distant from my partner .476
My sexual interest for my partner soon fades away .382
Frequently, I do not behave well to my partner .381
I take my partner for granted .380
I am not honest with my partner .379
I do not easily compromise .318
I find it difficult to communicate with my partner .313
Bad sex
Bad sex .482
Disagreements with my partner about how often we
have sex
.481
Sexual incompatibility with my partner .480
Frequent fights with my partner .422
Different goals with my partner .352
Behavioral issues
I have psychological problems .684
I often become violent to my partner .662
I have addictions—gambling, alcohol etc. .581
My parents/relatives intervene in my relationship .405
Character issues
I am quirky .578
I am selfish .512
I am always complaining to my partner .350
My insecurities .332
I often break out on my partner .332
My character .306
Fading away enthusiasm
I find the relationship’s routine tiring .578
My enthusiasm soon fades away .560
I am not a routine person .536
I get bored quickly .480
I am not patient .363
My feelings of romantic love soon fades away .328
My passion soon fades away .328
Children
My children are absorbing much of my energy, and not
much is left for my relationship
.617
My partner allocates most of his/her time to our children
and very little to me
.589
Frequent disagreements with my partner about how to
raise our children
.493
Social circle issues
My partner does not have good relationships with my
parents and relatives
.600
I do not have good relationships with my partner’s
parents and relatives
.587
My partner does not have good relationships with my
friends
.582
(continued)
Table 1. (continued)
Factors
Factor
loadings
I do not have good relationships with my partner’s
parents and relatives
.437
I have different interests from my partner .325
Lack of personal time and space
I feel that my partner is oppressing me .548
I want to have more personal time and space .465
I feel that a relationship constrains me .413
My partner always nagging .410
My partner constrains me .378
I am tired of constantly reporting on where I am and
what I do
.369
Infidelity and abuse
My partner’s infidelities .781
My partner is physically violent .757
My partner lacks sexual interest for me .377
Clinginess
I become easily dependent on my partner .626
I am too clingy .616
I tend to adapt to my partner’s needs without
considering my own
.438
I try to exercise constant control on my partner .409
I am jealous of my partner .398
I expect too much from my partner .343
Not monogamous
I feel that I miss opportunities to get different
experiences when I am in a relationship
.503
It is difficult for me to be monogamous .490
I keep making comparisons with my previous relationships .414
I cannot resist temptations .388
I get bored having sex with the same person .377
I find it tiring to be with the same person all the time .363
I easily break up if I do not like something .304
Long work hours
I spend many hours working .594
I do not have much time available for my partner .501
I often put my career on top of the relationship .437
6Evolutionary Psychology

composingeach factor as the dependent variables, the sex and the
marital status as the independent categorical variables, and the
age and the number of children as the continuous independent
variables. Note that, for the marital status variable, we did not
include the “widowed” category as it had only eight observations.
Overall, 12 test were performed, one for each factor. In order to
avoid the problem of ainflation arising from multiple compar-
isons, Bonferroni correction could be applied, setting the ato .004
(.05/12). Accordingly, the reader may choose to consider as
non-significant any effect that was above this level.
The results are presented in Tables 2 and 3, where we can
see that, for most factors, significant sex-differences were
found. For some factors such as “Lack of effort,” men gave
higher scores than women, while for others such as “Children,”
women gave higher scores than men. In general, however, men
tended to give higher scores than women. For the “Infidelity
and abuse” where the mean scores were similar for the two
sexes, the sex-difference was predominantly located over the
“My partner lacks sexual interest for me” item, where men
gave higher scores (M¼2.78, SD ¼1.33) than women
(M¼2.54, SD ¼1.44). Moreover, significant age effects were
found for several factors. The direction of the age effect was
not consistent but changed across factors (see Table 3). More-
over, the number of children was significant for the “Children”
factor, with a positive regression coefficient sign, indicating
that the more children participants had, the higher scores they
gave to the items composing this factor. Finally, the marital
status came significant for most factors. With respect to the
“Children” factor, post-hoc analysis using Bonferroni indicated
that, participants who were married gave significantly higher
scores than participants who were in a relationship. For the
remaining cases, participants who were married and in a rela-
tionship gave significantly higher scores than participants who
were single and divorced.
Table 2. The Hierarchy of Factors and Sex Effects in Study 2.
Overall Women Men
Factors %Mean (SD) Mean (SD) Mean (SD) p-value Z
p2
Fading away enthusiasm 31.6 2.68 (0.81) 2.62 (0.82) 2.76 (0.79) .001 .024
Long work hours 29.9 2.66 (0.92) 2.59 (0.94) 2.73 (0.90) .012 .010
Lack of personal time and space 31.0 2.61 (0.93) 2.50 (0.93) 2.73 (0.90) .002 .020
Character issues 23.9 2.57 (0.80) 2.64 (0.82) 2.49 (0.75) <.001 .026
Clinginess 21.6 2.51 (0.76) 2.52 (0.81) 2.50 (0.69) .353 .006
Bad sex 28.9 2.50 (1.02) 2.46 (1.05) 2.55 (0.98) .050 .011
Infidelity and abuse 24.0 2.28 (1.27) 2.28 (1.36) 2.29 (1.15) .005 .012
Children 19.8 2.24 (1.02) 2.26 (1.06) 2.22 (0.98) <.001 .022
Lack of effort 17.7 2.22 (0.86) 2.13 (0.88) 2.31 (0.84) <.001 .052
Social circle issues 14.9 2.15 (0.84) 2.11 (0.85) 2.21 (0.82) .073 .010
Not monogamous 16.0 2.12 (0.93) 1.94 (0.88) 2.32 (0.95) <.001 .046
Behavioral issues 10.4 1.76 (0.97) 1.72 (0.98) 1.81 (0.97) <.001 .023
Table 3. Age, Marital Status and Number of Children Effects in Study 2.
Age Marital status Number of children
Factors p-value Z
p2
p-value Z
p2
p-value Z
p2
Fading away enthusiasm .375 .007 .014 .012 .104 .011
Long work hours (*) <.001 .017 .002 .008 (þ) .024 .009
Lack of personal time and space .201 .008 <.001 .020 .277 .007
Character issues .266 .008 <.001 .020 (þ) .043 .013
Clinginess .120 .010 .111 .008 .116 .010
Bad sex (þ) .003 .017 <.001 .021 .816 .002
Infidelity and abuse (þ) .019 .009 <.001 .013 .982 .000
Children (þ) .003 .014 .002 .009 (þ) <.001 .036
Lack of effort .155 .018 <.001 .029 .233 .016
Social circle issues (þ) .036 .011 <.001 .016 .466 .004
Not monogamous .639 .005 <.001 .022 .553 .006
Behavioral issues (-) .006 .014 .009 .008 (þ) .019 .011
Note. The sign inside the parenthesis next to the p-value indicates the direction of the relationship.
*a significant effect of age with a negative sign was found for the “I do not have much time available for my partner” item, and a similar effect with a positive sign for
the “I spend many hours working” item.
Apostolou and Wang 7

Discussion
In the current research, we have identified 78 difficulties in
keeping and intimate relationship, and we have classified
them in 12 broader factors. We have also found that enthu-
siasm and romantic feelings fading away quickly, along
with long work hours and lack of personal time and space,
were considered as the most important factors causing dif-
ficulties to people in keeping an intimate relationship. In
addition, almost 70%of the participants indicated that at
least one factor, and 41%indicated that three or more fac-
tors, caused them difficulties. Significant sex, age marital
status and number of children effects were found for most
of the factors.
The mismatch between ancestral and modern conditions
is likely to account for many of the factors that have
emerged here. In more detail, in the ancestral context,
enthusiasm and intense romantic feelings would motivate
people to start a relationship, and they are expected to
reside as the relationship progresses. In a pre-industrial con-
text, the support, protection and subsistence benefits would
take over, providing the incentive to people to keep the
relationship. The absence of these factors in the
post-industrial context, makes the fading away of enthusi-
asm and romantic feelings impairing for keeping a relation-
ship, as people lose the incentive to do so.
In the same vein, because in the ancestral context the
benefits from having a family largely outweighed the costs
of having unpleasant personality traits, positive selection
forces would be relatively weak on personality traits that
make an individual more pleasant as a partner. Thus, in the
context of romantic relationships, several people today, are
not easygoing, are selfish, insecure, clingy and aggressive,
traits, which impair their capacity to keep an intimate rela-
tionship since their partners are not very willing to overlook
them. For instance, being physically aggressive is not tol-
erated in the contemporary context where individual rights
are well-protected and women are not dependent on their
partners, having thus the opposite effect: Women would
most likely walk away from an abusive partner. Further-
more, in ancestral human societies, people lived in extended
families, meaning that they had many people around which
could help them with raising their children (Hrdy, 2008). In
post-industrial societies, people usually live on their own,
away from their families, and they have to bear themselves
the bulk of the demands for raising their children. Thus,
selection forces may not have adequately prepared them
to do so and keeping at the same time an intimate
relationship.
The factors that we have identified in the present study,
reflect also conflict between the sexes. People adopt a
mixed mating strategy that involves extra-pair relationships
in order to increase their own at the expense of their part-
ners’ fitness. Accordingly, as it can be seen in the
“Infidelity and abuse” factor, a partner’s adoption of such
strategy makes keeping the relationship difficult. Although
conceptually distinct, being physically abusive loaded to the
same factor as infidelity. One possible explanation is that, a
male extra-pair infidelity may be coupled with physical
aggression, a strategy which, in an ancestral context, could
have prevented women from walking away from their
unfaithful partners. The conflict between the sexes is also
reflected in factors such as “Long work hours”: Being more
wealthy and successful could enable individuals, especially
men, to attract higher mate value long-term partners or a
higher number of casual ones. In effect, people may over-
emphasize on their careers in order to achieve status and
wealth, neglecting their current partner.
The extracted factors reflect also the adoption of a
short-term mating strategy. This is more obvious in the “Not
monogamous” factor, where people indicated that they were
not monogamous, and as a consequence, they tended to have
unsatisfactory sexual lives when they stay long in a rela-
tionship, and for this reason tend to break up easily. This
factorisalsoreflectedinthe“Fadingawayenthusiasm”:In
order to be able to adopt a short-term mating strategy, peo-
ple’s romantic feelings are expected to be intense when they
meet a new partner, but to reside quickly, motivating them
to look for other partners. Such calibration of behavioral
mechanisms would prevent people from keeping an intimate
relationship.
Sex-differences were found in almost all factors, suggest-
ing that men and women differed in how important they
considered the various difficulties. As it was originally pre-
dicted, men would be more likely to adopt a short-term and a
mixed mating strategy, which would cause them difficulties
in keeping an intimate relationship. These difficulties were
reflected in the “Not monogamous” and the “Infidelity and
abuse” factors. They were also reflected in the “Fading away
enthusiasm” and the “Lack of personal time and space” fac-
tors, where men gave significantly higher scores than women.
For instance, as discussed in the introduction, men’s enthu-
siasm may fade away quickly, so that they could move on to
the next partner. Also, in order to be able to have multiple
partners, men would prefer to have more freedom of move-
ment, and less control by a partner, and these preferences
reflect on the “Lack of personal time and space.” As indi-
cated by the effect size, the largest sex-difference was found
for the “Lack of effort,” which also reflects this issue as
items such as “My sexual interest for my partner soon fades
away” loaded there. This factor may also reflect the different
evolutionary histories of men and women: During most of
evolutionary time, men monopolized women by force, so
they may not have evolved to have high empathy and under-
standing of their partners’ needs.
Significant age effects were found for several factors. As
indicated by the effect size, the largest difference was for the
“Bad sex” and the “Long work hours” factors. Starting from the
former, older participants gave higher scores than younger
8Evolutionary Psychology

ones. One possible explanation is that, the more time people
spend in a relationship, the more likely it is for them to get
bored having sex with the same partner. Age in this case prob-
ably acts as a proxy of the length of the relationship, with older
participants being more likely to be longer in an intimate rela-
tionship than younger participants. With respect to the “Long
work hours” factor, we found that older participants spent more
time working and less time allocating to the partners than
younger participants. One possible explanation is that, as peo-
ple get older, they are more likely to advance in their careers,
and have then to spend more hours working and fewer hours
being with their partners.
We also found that participants who had more children gave
higher scores for difficulties such as their children absorbing
most of their time and energy than participants with fewer or no
children. This is expected, as people would allocate less
resources in child-rearing and would be less likely to disagree
with their partners on how to raise their daughters and sons, if
they had few or no children than if they had several children.
We also found that, participants who were single and divorced,
gave significantly higher scores in most factors than partici-
pants who were married and in a relationship. One possible
interpretation of this finding is that, individuals who experi-
enced more difficulties, were more likely not to be in a rela-
tionship than individuals who experienced fewer difficulties.
For instance, people who did not make considerable effort to
keep a relationship, were not monogamous, and they felt that a
relationship constrained them, were less likely to keep an inti-
mate relationship than people who made considerable effort,
were monogamous and they did not feel that a relationship
constrained them. Future research needs to investigate this
finding further.
The means for all factors were below the middle of the scale
(i.e., “3”), suggesting that each one on its own was not causing
people considerable difficulties in keeping a relationship. Yet,
each mean was accompanied by a relatively large standard
deviation, indicating that there was considerable variation in
these difficulties, with some people finding them very con-
straining and others not constraining at all. On the basis of
these findings, we can argue that people will experience severe
difficulties in keeping a relationship when more than one fac-
tors is present. For instance, if people are quirky, have a taste
for sexual variation, and lose their enthusiasm quickly, they
will face severe difficulties in keeping a relationship, but peo-
ple who are say only quirky, may manage to do so more
smoothly. Of course, the outcome depends also on the severity
of the problem; if people are for instance extremely quirky,
they will face severe difficulties in keeping a relationship even
in the absence of other difficulties.
As discussed above, the difficulties that people face in keep-
ing an intimate relationship could lead to divorce. Such diffi-
culties could cause the termination of the relationship long
before it reaches the point of marriage, leading people to
remain single. They may also prolong the spells of singlehood,
because people who face such difficulties may had bad experi-
ences from being in a relationship, which could demotivate
them from looking to establish new ones. Actually, one study
asked participants to indicate the reasons why they were single,
and found that bad experiences from previous relationships was
a common reason (Apostolou, 2017b). Accordingly, studying
the difficulties in keeping intimate relationships is necessary
for developing interventions that could enable people to main-
tain an intimate relationship. A proper theoretical framework
for understanding these difficulties is key for this endeavor to
succeed. For instance, the evolutionary theoretical framework,
developed in the current paper, indicates that most of these
difficulties arise from behavioral mechanisms not being
well-adapted to the modern conditions rather than from beha-
vioral mechanisms being broken. That is, in most cases of
people facing difficulties in keeping an intimate relationship,
there is not an underlying pathology. In turn, possible interven-
tions should not aim to identify and “cure” a pathology, but to
enable instead people to address the limitations of their beha-
vioral adaptations, and function better in the contemporary
environment.
Our research is not without limitations. To begin with,
our results were based on self-report data that are subject to
several biases. In particular, people may not have an accu-
rate perception of what causes them difficulties in keeping
an intimate relationship. For instance, people may fail to
recognize that they are clingy, which in turn, makes keeping
a relationship difficult. Furthermore, we employed a
non-probability sample, so our findings cannot be readily
generalized to the population. Also, although we have
employed a combination of qualitative research methods
in order to identify the reasons which caused people diffi-
culties in keeping an intimate relationship, we may not have
captured all of them. Moreover, the importance ascribed to
these reasons may vary with the cultural context, which
indicates that cross-cultural research is required for examin-
ing cultural variation. In addition, our study is explorative
and was based one sample. Consequently, the next step in
this research should be to employ these results and system-
atically develop a theoretically-driven measure, with care-
fully generated items, a good and a priori specified factor
structure, and good measurement properties. Finally yet
importantly, we did not control for sexual orientation. Given
the relatively low prevalence of homosexuality and bisexu-
ality (LeVay, 2010), we expect that our sample was predo-
minantly heterosexual. Accordingly, our findings may not
generalize to non-heterosexual individuals.
The plethora of reasons and factors that we have identified
in the current research, testify to the complexity of the phenom-
enon. Such complexity suggests that our work is insufficient
for fully understanding the difficulties that people face in keep-
ing an intimate relationship. It should be considered thus, as the
first of the many studies which are required to understand this
fascinating phenomenon.
Apostolou and Wang 9

Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to
the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, author-
ship, and/or publication of this article.
ORCID iD
Menelaos Apostolou https://orcid.org/0000-0002-0685-1848
Yan Wang https://orcid.org/0000-0003-3664-7933
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Appendix
Table A. The Correlation Matrix for the Factors Extracted in Study 2.
Factors
Lack of
effort
Bad
sex
Behavioral
issues
Character
issues
Fading away
enthusiasm Children
Social
circle
issues
Lack of
personal time
and space
Infidelity
and
abuse Clinginess
Not
monogamous
Long
work
hours
Lack of effort 1 .601*
*
.562*
*
.647*
*
.671*
*
.497*
*
.647*
*
.609*
*
.513*
*
.516*
*
.569*
*
.487**
Bad sex .601*
*
1 .428*
*
.434*
*
.486*
*
.573*
*
.607*
*
.672*
*
.695*
*
.407*
*
.629*
*
.338**
Behavioral issues .562*
*
.428*
*
1 .528*
*
.472*
*
.359*
*
.489*
*
.445*
*
.489*
*
.494*
*
.600*
*
.342**
Character issues .647*
*
.434*
*
.528*
*
1 .549*
*
.369*
*
.466*
*
.490*
*
.371*
*
.576*
*
.502*
*
.424*
*
Fading away enthusiasm .671*
*
.486*
*
.472*
*
.549*
*
1 .336*
*
.472*
*
.632*
*
.339*
*
.404*
*
.676*
*
.503*
*
Children .497*
*
.573*
*
.359*
*
.369*
*
.336*
*
1 .533*
*
.468*
*
.507*
*
.374*
*
.391*
*
.374*
*
Social circle issues .647*
*
.607*
*
.489*
*
.466*
*
.472*
*
.533*
*
1 .594*
*
.504*
*
.476*
*
.552*
*
.349*
*
Lack of personal time and space .609*
*
.672*
*
.445*
*
.490*
*
.632*
*
.468*
*
.594*
*
1 .510*
*
.414*
*
.691*
*
.472*
*
Infidelity and abuse .513*
*
.695*
*
.489*
*
.371*
*
.339*
*
.507*
*
.504*
*
.510*
*
1 .378*
*
.509*
*
.239*
*
Clinginess .516*
*
.407*
*
.494*
*
.576*
*
.404*
*
.374*
*
.476*
*
.414*
*
.378*
*
1 .419*
*
.320*
*
Not monogamous .569*
*
.629*
*
.600*
*
.502*
*
.676*
*
.391*
*
.552*
*
.691*
*
.509*
*
.419*
*
1 .397*
*
Long work hours .487*
*
.338*
*
.342*
*
.424*
*
.503*
*
.374*
*
.349*
*
.472*
*
.239*
*
.320*
*
.397*
*
1
Note. *significant at .050; **significant at .001.
10 Evolutionary Psychology

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