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I’m working on a social science discussion question and need an explanation and answer to help me learn.

1.What is the topic area?

2.Why is the research interesting or needed?

3.What was the authors’ hypothesis?

4.What did they do (a brief summary of how they collected their data—again, in your own words)?

5.What did they find?

6.What does it mean? How does it apply to our knowledge of human behavior/psychology

Proc. R. Soc. B (2010) 277, 3501–3508
Published online 16 June 2010
Sex, drugs and moral goals: reproductive
strategies and views about recreational
Robert Kurzban1,*, Amber Dukes3 and Jason Weeden2
Department of Psychology, and 2Pennsylvania Laboratory for Experimental Evolutionary Psychology,
University of Pennsylvania, Philadelphia, PA 19104, USA
University of Central Florida, Orlando, FL, USA
Humans, unlike most other species, show intense interest in the activities of conspecifics, even when the
activities in question pose no obvious fitness threat or opportunity. Here, we investigate one content
domain in which people show substantial interest, the use of drugs for non-medical purposes. Drawing
from two subject populations—one undergraduate and one Internet-based—we look at the relationships
among (i) abstract political commitments; (ii) attitudes about sexuality; and (iii) views surrounding recreational drugs. Whereas some theories suggest that drug views are best understood as the result of
abstract political ideology, we suggest that these views can be better understood in the context of reproductive strategy. We show that, as predicted by a strategic construal, drug attitudes are best predicted by
sexual items rather than abstract political commitments and, further, that the relationship between factors
such as political ideology and drugs, while positive, are reduced to zero or nearly zero when items assessing sexuality are controlled for. We conclude that considering morality from the standpoint of strategic
interests is a potentially useful way to understand why humans care about third party behaviour.
Keywords: reproductive strategies; humans; mortality; drugs
A zoologically peculiar feature of humans is that people
not only monitor conspecifics’ activities across a wide
array of domains, but also express a desire that costs be
imposed on third parties for a wide variety of behaviours
(DeScioli & Kurzban 2009a). Humans do this even in circumstances in which they typically do not consciously
perceive—and indeed often expressly deny—that they
themselves (or their relatives) are harmed by the behaviour in question.
Our present interest is in one such category of activity,
namely, the use of recreational drugs. Why do some
people think that other people should be prevented from
using certain drugs—various chemical substances with
psychoactive properties that are smoked, injected or
otherwise consumed for recreational or other non-medical reasons—and punished if they do so? The studies
reported here explore the moral intuitions that give rise
to opposition to the use of these substances by others.
Unlike some categories of moral behaviour—for
example, those involving unprovoked physical harm, theft
and breach of contract, in which there is considerable
agreement regarding moral wrongness (Robinson et al.
2008)—there is substantial variation in opposition to the
sale and use of recreational drugs (Robinson & Kurzban
2007). For example, a Gallup Poll from 2009 found that
44 per cent of Americans favoured marijuana legalization,
while 54 per cent opposed it, which showed substantial
movement from the same item asked in 1969, when only
* Author for correspondence (kurzban@psych.upenn.edu).
Electronic supplementary material is available at http://dx.doi.org/10.
1098/rspb.2010.0608 or via http://rspb.royalsocietypublishing.org.
Received 22 March 2010
Accepted 25 May 2010
12 per cent of Americans favoured marijuana legalization,
while 84 per cent opposed it (Saad 2009).
Our primary purpose here is to investigate the sources
of the large amount of variation in views about recreational drugs. In addressing this puzzle, we shed light
as well on the related puzzle of why anyone at all ever
morally condemns the use of recreational drugs.
(a) Candidate models
Most work surrounding the evolved function of morality
focuses on conscience, putative mechanisms designed to
guide individuals’ own behaviour (de Waal 1996; Haidt &
Joseph 2004, 2007; Krebs & Janicki 2004). These
models focus on adaptive problems such as gathering
the benefits of cooperation, avoiding pathogens and
avoiding incest (Lieberman et al. 2003; Haidt & Joseph
Such models, however, have the potential to explain
the condemnation of others only obliquely. For example,
the fitness costs of incest explain why people—and other
organisms—have mechanisms designed to avoid having
sex with closely related individuals (Lieberman et al.
2003, 2007; Fessler & Navarrete 2004). This explanation
for incest-avoidance mechanisms does not, however, in
itself, explain why people want others to be punished for
committing incest.
That is not to say that such an explanation is not
possible. Lieberman (2007), for example, suggests that
incest-condemnation systems might be designed to
guide one’s kin away from this fitness-reducing behaviour.
Condemnation, on this view, benefits the individual’s
genes through the distal disincentivizing effects on related
others. More generally, one might argue that if
This journal is q 2010 The Royal Society
R. Kurzban et al.
Sex and drugs
moralization is applied to nearby individuals, and these
individuals are differentially likely to be friends, kin and
allies, condemnation can be explained.
A similar argument could be made regarding what
might be the most intuitive potential explanation regarding moralization of drugs, that they are harmful. Perhaps,
people oppose the use of drugs as a means of generating
benefits to others, particularly kin and allies. By imposing
costs on using drugs, people reduce the chance that
others will use harmful drugs, and so lead to net (indirect)
benefits. On this view, condemnation is an altruism
device. Related arguments could be made that the foundations of opposition to recreational drugs lie in
individuals’ desire to protect others from addiction or
criminal activities associated with drug use.
These explanations seem unlikely for at least two
reasons. First, people do not moralize a very large
number of activities that are dangerous. People do not
have the intuition that horseback riding, skiing, boxing,
skydiving and many other hazardous activities are
wrong, to say nothing about riding in cars or working at
construction sites or in coal mines. An explanation
located in harm requires an account of why using recreational drugs, but not other sorts of potentially
harmful modern activities, elicits condemnation.
Second, unlike moral intuitions regarding many other
domains (like unprovoked assault, theft, etc.), views on
recreational drugs are highly variable. Even if one were
to think that perceptions of the harmfulness of recreational drugs ultimately drive views on the morality
and preferred legality of recreational drugs, one is
still left in need of an explanation of the tremendous
variability in views.
(b) Variability
(i) Abstract political commitments as causes
The predominant model regarding the origin of variation in
political and moral views, including views surrounding recreational drugs, suggests that the source of individuals’
opinions are their more basic commitments to higher level
liberal-conservative ideology, political party affiliation,
values, religious views and related ‘symbolic’ items. Drawing
largely on the Standard Social Science Model’s (Tooby &
Cosmides 1992) view of culture and domain-general learning, this view suggests that people develop emotional
attachments to these relatively abstract factors through
social learning (Jacoby 2002; Janda et al. 2002; Bardes &
Oldendick 2003; Sears & Levy 2003; Erikson & Tedin
2005). Views on recreational drugs, along with many other
kinds of issues, are seen as downstream effects of these
abstract political commitments.
Haidt and colleagues have expanded the standard political models with their account of the five ‘foundations’
of morality (Graham et al. 2009). This view begins with
the idea that there are individual differences, including
important aspects of personality, as measured by the
Big Five inventories, and other kinds of variation, such
as disgust sensitivity. These differences give rise to
different weights to the five key areas of morality, which
Haidt & Joseph (2007) identify as harm, fairness,
purity, ingroup loyalty and hierarchy.
On Haidt and colleagues’ account, variations in ideological commitments are driven by underlying variations
Proc. R. Soc. B (2010)
in personality variables and moral foundations, with political liberals placing weight on only harm and fairness,
and political conservatives valuing all five moral foundations (Haidt & Kesebir 2010). Haidt and colleagues
do not argue with the primary claims of standard political
models insofar as both view individual issue opinions
as derived from more basic ideological and other
abstract items.
One of the fundamental claims flowing from the standard political model is that self-interest is rarely a strong
factor in accounting for political attitudes. The claim
has been most forcefully advanced by defenders of the
‘symbolic politics’ approach (e.g. Sears & Funk 1990)
and has become an often-repeated truism in political
science (e.g. Kinder 1998; Caplan 2007; Graham et al.
2009), though we give some reasons below to doubt the
stronger versions of the claim.
The view of abstract political commitments as causes
makes a number of familiar predictions. Specifically,
this view implies that self-interest is likely to be of little
relevance. Instead, more abstract political differences
will matter. In particular, compared with those people
who do not oppose the use of recreational drugs, those
who do will be more conservative, more religious and, following the framework of Haidt and colleagues’ work,
more driven by the moral salience of ingroup loyalty, hierarchy and perhaps, most importantly, purity, as well as, at
a deeper level, higher disgust sensitivity, less openness to
experience and related personality dimensions.
(ii) Reproductive strategies as causes
Our model of individual differences differs from these
approaches and is closely linked to the idea that the central phenomenon to be explained in the context of
morality is condemnation, rather than conscience. If
moral rules are construed as specifying classes of activities
or behaviours that, when someone engages in them, lead
to punishment without the possibility of subsequent
reprisal (P. DeScioli 2008, unpublished PhD thesis;
DeScioli & Kurzban 2009a), then moral rules are like
economic institutions, the rules that govern transactions
(Kurzban in press). Also, like economic institutions, the
contents of these rules have important consequences
that, crucially, differ from one individual to the next.
Just as institutions affect outcomes depending on one’s
position in an economy—for example, import duties
help domestic producers of particular goods by increasing
prices, and harm consumers of those goods for the same
reason—the content of moral rules has different effects
on individuals’ outcomes depending on the details of
the strategy one is implementing in the context of the
social world.
The idea that strategic interests matter in affecting
opinions has been demonstrated in political science.
Evidence in favour of this view comes from widely cited
facts that socioeconomic status is often a major predictor
of views on governmental redistribution of wealth through
social welfare programmes ( Janda et al. 2002; Erikson &
Tedin 2005). That is, people who disproportionately
benefit from redistribution programmes—the poor—
tend to support them, while people who disproportionately pay for such programmes—the rich—tend to
oppose them. Similarly, race is often a major predictor
Sex and drugs
of views on the desirability of public and private
preferences in favour of racial minorities (Flanigan &
Zingale 2002; Erikson & Tedin 2005).
To these often-cited axes of societal conflict, we add
another dimension driven by evolutionary analysis. This
axis is the conflict between those who pursue a committed
reproductive strategy with high levels of investment by
fathers in their children, and others who pursue a more
promiscuous reproductive strategy involving males who
devote substantially more of their time and resources to
obtaining additional mates rather than raising children.
Humans, like other species (e.g. Shuster 2010), deploy
different reproductive strategies depending on variation
in individual and ecological variables (Buss & Schmitt
1993; Gangestad & Simpson 2000). These differences
give rise to strategic conflict.
The primary point of conflict rests with the general
level of promiscuous sexual activity in a given social
group (see J. Weeden, 2003, unpublished PhD thesis;
Weeden et al. 2008). The interests of those pursuing a
more committed strategy are threatened by high levels
of promiscuity. Committed husbands stand to lose more
from cuckoldry because they invest more heavily in their
(putative) offspring. Committed wives incur higher costs
upon mate-abandonment, particularly when they have
larger numbers of young children combined with reduced
education and work-place participation. The interests of
committed strategists are advanced to the extent they
can impose larger social costs on promiscuous strategists.
Promiscuous strategists, by contrast, find their interests
advanced by minimizing these social costs and increasing
their number of potential mates.
Different people, then, depending on their own properties and opportunities, stand to lose or gain by virtue
of the moral institutions that govern sexual behaviour.
This pattern of gains and losses might have constituted
a selective pressure giving rise to a contingent psychology
that is designed to adopt—and attempt to cause others to
adopt—moral rules that facilitate one’s own competitive
reproductive strategy.
Note that these ideas begin to explain why there is relative homogeneity in some areas of moral condemnation.
In some cases, moral rules are more or less what we
might call Rawlsian (Rawls 1971), benefitting the large
majority of people. For instance, rules that specify punishment for intentional physical harm—and therefore
disincentivize intentional harm—benefit almost all
people because everyone is vulnerable to being harmed.
Some rules, however, more clearly help some and hurt
others. This generates an incentive for individuals to
adopt, and try to cause others to adopt, rules that work
in favour of their interests.
A key context for moralistic conflicts over sexual matters in developed societies is found with respect to
religious commitments. Political discussions often mention religiosity as a major predictor of social or cultural
issues (like premarital sex, abortion or pornography)
(e.g. Corbett & Corbett 1999; Flanigan & Zingale
2002; Erikson & Tedin 2005). It is usually assumed that
differences in socialization lead to adult differences in religiosity, which themselves lead to different issue opinions.
However, Weeden et al. (2008) tested the model that
claims causality running from religiosity to sexual and
family attitudes and behaviours against an evolutionarily
Proc. R. Soc. B (2010)
R. Kurzban et al.
motivated model that reversed the usual causal assumption, viewing differences in reproductive strategy as a
key determinant of individuals’ decisions to increase or
reduce affiliation with religious groups. They found, consistent with the evolutionary model, that differences in
reproductive strategies almost fully mediated well-known
relationships between religiosity on the one hand and
gender, age, cohort and Big five personality variables on
the other hand, suggesting strongly that the causal
arrow runs at least in substantial part from reproductive
lifestyles to religiosity.
Taken together, these ideas suggest that one component of evolved moral psychology is designed to
increase or decrease the chances that particular moral
regimes operate in one’s social environment, involving
centrally one’s own adoption or rejection of a given
moral view. We propose that there are mechanisms
designed to make inferences about the costs and benefits
to oneself of different rule regimes, and endorse those
rules that benefit oneself.
Why should recreational drugs elicit such differences
in views about wrongness? Our answer is that it is
linked to promiscuity. Among young Americans, for
example, the substantial link between promiscuous
sexual behaviour and recreational drug usage is well
established (e.g. Lammers et al. 2000; Whitaker et al.
2000; Weeden & Sabini 2007). In our view, efforts to
limit recreational drug usage flow in large part from
attempts by committed reproductive strategists to
reduce levels of sexual promiscuity because promiscuity
interferes with committed strategies. Thus, we expect
the relationship between attitudes towards recreational
drugs and attitudes towards promiscuity to be very
large, and to dominate other correlates of opinions on recreational drugs, including more abstract items like
religiosity and political ideology.
(iii) Predictions of the models
These two models make different predictions regarding
the relationships among individuals’: (i) abstract political
views and commitments, (ii) attitudes and behaviours
surrounding sexuality and (iii) attitudes toward drugs.
Suppose that abstract political views are the causal
antecedents of views toward various sociopolitical
realms, including those associated with both sexual behaviour and drug use. If this were the correct causal
account, then the variation in views surrounding sexuality
would have similar causal antecedents to the variation in
views surrounding recreational drug use. There should
be strong relationships between abstract political views
and both attitudes surrounding sex and attitudes towards
drugs. We should also expect strong relationships between
attitudes toward sex and attitudes toward drugs, since
they have similar causal antecedents. In addition, and
crucially, if this is the correct causal account, if we look
at the relationship between sexual attitudes and drug
use attitudes, controlling for abstract political commitments,
then the relationship between sexual attitudes and drug
use attitudes should be reduced to a substantial degree
(see the first model in figure 1).
Compare this prediction to the counterintuitive prediction one would make if attitudes about recreational drugs
are driven by sexual strategies. If this view is correct, then
R. Kurzban et al.
Sex and drugs
graphical representation
when controlling for abstract political views, partial correlations between sexual
strategy and drug attitudes will be substantially diminished.
when controlling for sexual strategy, partial correlations between abstract
political views and drug attitudes will not be substantially diminished.
when controlling for abstract political views, partial correlations between sexual
strategy and drug attitudes will not be substantially diminished.
when controlling for sexual strategy, partial correlations between abstract
political views and drug attitudes will be substantially diminished.
abstract political views
same as above for sexual strategy as causal.
sexual strategy
drug attitudes
Figure 1. Graphical representations of three different causal pathways that might give rise to variation in people’s views regarding recreational drugs. Boxes correspond to categories of cognitive representations (e.g. beliefs and attitudes), and arrows
correspond to causal processes that give rise to other categories of representation. One possibility (top) is that abstract political
views (e.g. conservatism) are causal, giving rise to particular views about sexuality and drugs. A second possibility (middle) is
that representations associated with sexuality are causal, giving rise to abstract political views and views surrounding drugs. A
third possibility (bottom) is that sexual attitudes are mediators, such that abstract political views strongly influence sexual strategy and sexual strategy strongly influences drug attitudes, with no direct causal link between abstract political views and drug
attitudes. Empirical predictions of each causal pathway are indicated. These models are not intended to be exhaustive.
there will be relationships between political views (e.g. liberalism) and drugs, but this relationship will be driven by
the fact that they share a common underlying cause,
located in sociosexuality. This leads to the prediction
that the relationship between sexual attitudes and drugrelated views will not be substantially diminished when
one controls for abstract political commitments. In
addition, this view predicts that the relationship between
opinions on recreational drug use and abstract political
commitments will be substantially reduced when one controls for sexual attitudes. That is, if sexual attitudes are
the common causal antecedent of both abstract political
views and drug attitudes, controlling for sexual attitudes
should strongly attenuate this relationship (see the
second model in figure 1).
This view cannot be distinguished in our study from the
view that abstract commitments causally influence attitudes towards promiscuity, which in turn causally
influence attitudes towards drugs (see the third model in
figure 1). However, this model and our model both share
the fundamental premise that sociosexual differences largely drive differences in moral opinions regarding
recreational drug usage, with little direct influence from
abstract commitments to recreational drug attitudes.
In summary, our hypothesis is that the intuition that
recreational drug use should be prohibited derives primarily (though, we are careful to note, not exclusively)
from the relationship between these drugs and sexual
promiscuity. People’s moral intuitions are (in part)
Proc. R. Soc. B (2010)
designed to control and constrain others’ sexual activity
in accordance with one’s own reproductive strategy.
Because recreational drug usage is strongly associated
with greater promiscuity, people oppose recreational
drugs as one part in a larger effort to control others’
sexual activity. Therefore, we predict that moral attitudes
toward drugs will closely relate to variables such as liberalism/conservatism, religiosity, and so on, but that these
relationships will be strongest with respect to items that
measure correlates of one’s sexual strategy. Further,
controlling for promiscuity attitudes, we predict that
other relationships between views about drugs and
abstract variables will be substantially diminished, or
even disappear entirely.
(a) Undergraduate sample
We analysed data from two samples. The first was an undergraduate sample consisting of students from a large university
in the southeastern United States. Responses were collected
from 516 undergraduate students. The average age was
19.5 (s.d. ¼ 2.16) and the sample was 69 per cent female.
The sample contained 70 per cent European Americans,
13 per cent Latino Americans, 9 per cent African Americans,
5 per cent Asian Americans and 3 per cent other. All students
were enrolled in at least one undergraduate psychology
course. Participants received extra credit for participating
in the study.
Sex and drugs
(b) Mturk sample
Participants in the second sample were 471 individuals
recruited from a web-based recruitment site, Amazon’s
‘Mechanical Turk’, or Mturk. Mturk is a ‘crowdsourcing’
website that allows people to perform short tasks for small
amounts of money. Anyone over 18 may use the site. The
survey was restricted to residents of the United States. In
other work, this site has generated results comparable to
other samples (e.g. DeScioli & Kurzban 2009b). The average
age was 32.9 (s.d. ¼ 11.8) and the sample was 65 per cent
female. The sample contained 81 per cent European
Americans, 5 per cent African Americans, 5 per cent Asian
Americans, 4 per cent Latino Americans and 5 per cent other.
(c) Questionnaire items
Our measure of recreational drug attitudes consisted of nine
items, including attitudes towards the morality and legal
status of using marijuana, cocaine and Ecstasy, as well as
general attitudes towards recreational drugs. The exact
items differed somewhat for the two samples and are provided in the electronic supplementary material. The
recreational drug scale was coded such that opposition to recreational drugs is indicated by larger values. The scale had a
Cronbach’s alpha of 0.87 in the undergraduate sample and
0.88 in the Mturk sample.
We used a modified version of the Sociosexual Orientation
Index (Simpson & Gangestad 1991), for which we eliminated the item regarding how many one-night stands they
have had (we find that participants are confused by the wording of this item), and added an item on participants’ number
of non-intercourse (hook-up) partners in the past 3 years, in
addition to breaking out number of past sexual partners
into heterosexual and homosexual partners. The resulting
scale (‘Sociosexuality’) had a Cronbach’s alpha of 0.83 in
the undergraduate sample and 0.80 in the Mturk sample.
Participants completed the Three-Domain Disgust Scale
(Tybur et al. 2009), which produces three sub-scales
involving sexual disgust (‘Disgust—sexual’; Cronbach’s
alpha of 0.84 in the undergraduate sample and 0.86 in the
Mturk sample), moral disgust (‘Disgust—moral’; Cronbach’s
alpha of 0.86 in the undergraduate sample and 0.88 in the
Mturk sample) and pathogen disgust (‘Disgust—pathogen’;
Cronbach’s alpha of 0.80 in the undergraduate sample and
0.83 in the Mturk sample).
Participants reported their overall liberal/conservative political identification on a seven-point scale (‘Politics—
ideology’). Participants also rated their support/opposition
(on a seven-point scale) to a number of current political
issues. We broke these out into sexual issues, including
restrictions against Internet pornography, comprehensive
sex education in public schools, banning abortion and legalized gay marriage (‘Politics—sexual items’; Cronbach’s
alpha of 0.64 in the undergraduate sample and 0.71 in the
Mturk sample), and non-sexual issues, including allowing
undocumented immigrants to stay in the United States,
higher taxes for the wealthy, aggressive military response to
dangerous foreign groups, unemployment payments, gun
control laws, offshore drilling and subsidized healthcare for
the poor (‘Politics—non-sexual items’; Cronbach’s alpha of
0.66 in the undergraduate sample and 0.72 in the Mturk
sample). Participants also completed the 16-item Social
Dominance Orientation scale (Pratto et al. 1994)
(Cronbach’s alpha of 0.94 in the undergraduate sample
and 0.93 in the Mturk sample).
Proc. R. Soc. B (2010)
R. Kurzban et al.
Participants completed the moral relevance items from
Graham et al. (2009), which are designed to fall into five subscales: harm (‘Moral relevance—harm’; Cronbach’s alpha of
0.86 in the undergraduate sample and 0.80 in the Mturk
sample); reciprocity (‘Moral relevance—reciprocity’;
Cronbach’s alpha of 0.83 in the undergraduate sample and
0.79 in the Mturk sample); ingroup (‘Moral relevance—
ingroup’; Cronbach’s alpha of 0.84 in the undergraduate
sample and 0.86 in the Mturk sample); hierarchy (‘Moral relevance—hierarchy’; Cronbach’s alpha of 0.83 in the
undergraduate sample and 0.79 in the Mturk sample); and
purity (‘Moral relevance—purity’; Cronbach’s alpha of 0.87
in the undergraduate sample and 0.88 in the Mturk sample).
We measured religiosity with a five-item scale asking
about level of religiosity, level of spirituality, frequency of private prayer, frequency of current church attendance and
expected future frequency of church attendance (‘Religiosity’; Cronbach’s alpha of 0.92 in the undergraduate sample
and 0.89 in the Mturk sample). We also asked a short version
of the Big five personality items (Rammstedt & John 2007).
Tables 1 and 2 show relationships between recreational
drug attitudes and other variables, with table 1 for the
undergraduate sample and table 2 for the Mturk
sample. Our primary prediction was that items tracking
attitudes towards sexual promiscuity as a group would
be larger correlates and would reduce the effects of the
other variables to a greater extent than the other variables
would reduce the effects of the sexual variables in partial
correlations. The prediction held—the largest correlations
in both samples involve sociosexuality, sexual disgust and
opinions on sexual political items, and controlling
for these sexual variables in partial correlations reduced
the size of the relationships between recreational
drug attitudes and most of the other variables
As a less formal confirmation that these correlations
are largely driven by promiscuity attitudes, we also examined correlations between each individual predictor item
(including sexual and non-sexual items) and recreational
drug attitudes. For the undergraduate sample, the top
three individual item correlates with recreational drug
attitudes were the following: ‘Sex without love is OK’
(from the sociosexuality scale; r ¼ 20.45); ‘Bringing
someone you just met back to your room to have sex’
(from the sexual disgust scale; r ¼ 0.44); and ‘I can imagine myself being comfortable and enjoying ‘casual’ sex
with different partners’ (from the sociosexuality scale;
r ¼ 20.41). For the Mturk sample, the top three individual item correlates with recreational drug attitudes were
the following: ‘Bringing someone you just met back to
your room to have sex’ (from the sexual disgust scale;
r ¼ 0.51); ‘Sex without love is OK’ (from the sociosexuality scale; r ¼ 20.50); and ‘Tougher restrictions against
pornography on the Internet’ (from the sexual politics
scale; r ¼ 0.47).
The principle result is that we find evidence that differences in sociosexuality are central to explaining
differences in attitudes toward recreational drugs. The
R. Kurzban et al.
Sex and drugs
Table 1. Correlations and partial correlations between recreational drug attitudes and other items from undergraduate sample
(n ¼ 516).
correlations with
recreational drug
partial correlations
(controlling for non-sexual
partial correlations
(controlling for sexual
politics—sexual issues
moral relevance—
moral relevance—
moral relevance—
moral relevance—
moral relevance—
social dominance
0 –0.02
*p , 0.01.
**p , 0.001.
best predictors of drug attitudes were not responses to
abstract political items, but rather items that asked
about matters relating to promiscuity. This provides evidence that views on sex and views on drugs are very
closely related.
Moreover, the relationship between sex and drugs
tended to mediate items that, from the perspective of
canonical views in political science, might have been
thought to be driving views on drugs. For instance,
while it is true, as one might have expected, that people
who are more religious and those who are more politically
conservative tend to oppose recreational drugs, in both
our samples, the predictive power of these religious and
ideological items was reduced nearly to zero by controlling for items tracking attitudes toward sexual
These reductions are difficult to reconcile with a model
in which abstract political views are the underlying causal
variables driving attitudes toward drugs. They are, however, consistent with the model we propose, in which
individuals’ sexual strategies drive views on recreational
It is also plausible given our results that abstract commitments drive sexual attitudes and sexual attitudes drive
drug attitudes. In both models, sexual attitudes directly
influence drug attitudes, with the difference being that
our model views sexual strategy as a major causal influence in determining abstract commitments, while the
other model takes the opposite causal position, viewing
Proc. R. Soc. B (2010)
items like religiosity and ideology as major influences in
determining sexual attitudes. We note that recent work
with regard to religiosity shows substantial evidence that
the causal arrow runs at least in significant part from
sexual lifestyles and attitudes to religious commitments
(McCullough et al. 2005; Weeden et al. 2008; Li et al.
2009). In addition, although not the preferred model,
political scientists occasionally view liberal-conservative
identifications not as generative ideological systems, but
as post hoc descriptions of pre-existing views on a range
of political items (e.g. Conover & Feldman 1981).
Of course, the present results should be treated with
the usual caution. Although our results replicated with
two distinct sample populations, it would be of value to
determine if other samples, perhaps in a cultural milieu
with different mores surrounding sex and recreational
drugs, would be of use. In places in which sexual behaviour and drug use are not closely linked, we would predict
that the effects we observed here would diminish.
Further, there is substantial variance left unexplained,
and future work should aim to identify sources of this
residual variation. One possibility is local variation in
the relationship between drug use and crime. In places
where this relationship is strong, people might adopt
anti-drug views as a means of reducing crime. A second
possibility, related to the first, is that local variation in
the harmful health effects of drugs might also influence
anti-drug views (for example, if there is regional variation
in terms of which drugs are used). Finally, and perhaps
Sex and drugs
R. Kurzban et al.
Table 2. Correlations and partial correlations between recreational drug attitudes and other items from Mturk sample (n ¼ 471).
correlations with
recreational drug
partial correlations
(controlling for non-sexual
partial correlations
(controlling for sexual
sexual items
politics—sexual issues
non-sexual items
moral relevance—
moral relevance—
moral relevance—
moral relevance—
moral relevance—
social dominance
*p , 0.01.
**p , 0.001.
slightly counter-intuitively, it could be that in places with
very high drug use, opposition might be reduced because
any given person in such an environment is likely to have
friends and relatives involved with drug use. In such a
case, stricter drug laws might have adverse effects on
one’s friends and relatives.
As with all correlational studies, we cannot directly
infer causation from our data. We believe that the results
undermine particular causal accounts, and our view resonates with other findings, but we look forward to
experimental work that can address issues of causality
more directly. For instance, it could be that by manipulating people’s own perceptions of their mate value, their
moral intuitions surrounding sexuality—but not other
moral domains—could be affected.
In closing, we believe that the results presented here
speak to a broad biological puzzle. Humans monitor
third party behaviour, and work to have costs imposed
on third parties, even when individuals’ own interests
are not obviously at stake (DeScioli & Kurzban 2009a).
While activities such as recreational drug usage are
often viewed as ‘victimless’ misdemeanours, our analysis
implies that individuals’ competing interests are
nonetheless involved. The results described here imply
that third-party morality in contexts like condemnation
of recreational drug usage might be best understood in
the context of strategic dynamics, with individuals
influencing moral rules in a way that favours their own
competitive reproductive strategies.
Proc. R. Soc. B (2010)
We expect, then, that this relationship between sexual
strategy and moral stances will occur in other domains
in which moral contents inhibit others’ sexual behaviour.
These would include attitudes toward prostitution, sexual
education in school and abortion ( J. Weeden, 2003,
unpublished PhD thesis), all of which might have an
influence on the degree of promiscuous sexuality.
This is not to say that sexual strategy is the only strategic
dynamic that is relevant. There are many domains of life in
which interests diverge, and advantage can be gained through
influencing the rules that govern behaviour. As we indicated
above, differences in views on economic matters, for example,
might depend much more on wealth and income rather than
sexual strategy. Future work might benefit from approaching
moral commitments as deriving less from abstract political
and religious views, and more from the perspective of
strategic conflicts faced by an extremely social species.
This work was approved by the respective ethical review
boards at the University of Pennsylvania and the University
of Central Florida.
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