DOI: 10.1093/oxfordhb/9780190299323.013.30
Abstract: During the past century, social scientists have documented many cross-cultural sex differences in personality and behavior, quite a few of which now appear to be found in all human societies. However, contrary to most scientists’ expectations, these so-called universal sex differences have been shown to be more pronounced in Western industrial societies than in most non-Western developing societies. This chapter briefly reviews the evidence bearing on these findings and offers a biologically based theory that could help shed light on why cross-cultural sex differences exist. The following hypothesis is offered: The expression of many genes influencing sexually dimorphic traits is more likely among descendants of couples who are least closely related to one another. If so, societies in which out-marriage is normative (i.e., Western industrial countries) will exhibit a stronger expression of genes for sexually dimorphic traits compared to societies in which consanguineal marriages are common.
Keywords: social role theory, evolutionary theory, evolutionary neuroandrogenic theory, sex egalitarian societies, sex differences, personality traits
Check also Universal and Specific in the Five Factor Model of Personality. Jüri Allik and Anu Realo. In The Oxford Handbook of the Five Factor Model, edited by Thomas A. Widiger. http://www.bipartisanalliance.com/2018/03/contrary-to-predictions-from.html
And Gender Differences in Personality Traits Across Cultures: Robust and Surprising Findings. Paul T. Costa Jr., Antonio Terracciano, and Robert R. McCrae. Journai of Personality and Social Psychology, 2001, Vol. 81, No. 2,322-331. DOI: 10.1037//0022-3514.81.2.322
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This chapter focuses on better understanding numerous average sex differences in cognition and behavior. Because the phrase is used frequently, it is henceforth abbreviated with the acronym ASDCBs.
This abbreviation refers to any and all average sex differences in how
humans think and behave. For ASDCBs that appear to exist in all
societies and time frames, the term universal ASDCBs is used.
There are five parts to this
chapter. Part 1 documents that numerous universal ASDCBs now appear to
exist. Part 2 reviews evidence of how ASDCBs seems to vary in strength
over time and across countries. In Part 3, findings from cross-cultural
research on the nature of ASDCBs are described. Part 4 describes three
theories for explaining ASDCBs, one being strictly environmental and two
being of an evolutionary/biological nature. Part 5 explores how well
the three theories explain what current evidence suggests about ASDCBs,
as revealed in Parts 1–3.
In today’s fast-paced
communications world, some readers may simply be interested in this
chapter’s bottom line. For them, a brief conclusion section provides an
overview of all five parts of the entire chapter.
Part 1: Universal ASDCBs
Social scientists have been
searching for possible universal ASDCBs for many years, some with
expectations that few, if any, would be found (Kessler & McKenna, 1978;
(p. 498)
Mead, 1963).
Doubts about the existence of universal ASDCBs began to change in the
1970s with the publication of a book by Maccoby and Jacklin (1974). It
summarized findings from several thousand studies published up to the
early 1970s. Their review led them to identify four ASDCBs that seemed
to be present across all cultures: (a) superior verbal ability in
females, (b) greater visual–spatial ability in males, (c) better
mathematical ability in males, and (d) more physical aggression in
males.
Two decades later, a meta-analysis of thousands of additional studies was published by Feingold (1994). It brought him to confirm conclusions reached by Maccoby and Jacklin (1974)
and then to add five more universal ASDCBs. Females, he said, were more
anxious, friendly/gregarious, trusting of others, and tender-minded,
whereas males were more assertive.
A decade and a half after Feingold’s (1994)
meta-analysis was published, eight colleagues and I published a book in
which findings from more than 18,000 studies pertaining to sex
differences were summarized (Ellis et al., 2008).
Citations to the studies were organized into hundreds of different
tables, each one pertaining to a separate possible ASDCB. Many of the
tables had to do with strictly biological traits and included
information on nonhumans, neither of which are of concern here. The
majority of tables, however, actually pertained to some aspect of human
cognition or behavior. From these tables, evidence of 65 universal
ASDCBs was obtained. Methodologically, we designated an ASDCB as being
apparently universal if (a) at least 10 relevant studies had been
conducted and (b) each study without exception reported the same sex
difference to exist to a statistically significant degree. For those
interested in the details, each ASDCB is described in Ellis (2011a). To save space, here I merely provide a brief sketch of the nature of these 65 ASDCBs under seven subject headings:
- 1. Stratification and work: Twelve behavioral traits were identified having to do with social stratification or work. They indicate that males work longer hours outside the home and are more likely to be employed in a variety of “male-typical occupations” such as jobs of a supervisory, scientific, and engineering nature. Females, on the other hand, when employed outside the home, are more likely to work in people-oriented and caregiving occupations.
- 2. Drug consuming and illegal behavior: Central to the five traits under this category is that males consume more alcohol and engage in more criminal behavior than do females.
- 3. Social and play behavior: The general pattern seen in this category of 12 traits indicates that females are more cooperative and helpful to others throughout life and even in their childhood play activities. Males, on the other hand, tend to be more competitive and more prone to interact with members of the opposite sex in explicitly sexual ways.
- 4. Personality and general behavior: Seven personality and general behavior traits were identified. They boiled down to males throughout life being more inclined to explore their environments, to take greater physical risks, and to behave in hostile/aggressive ways toward one another. Females were found to be friendlier. In all the countries sampled, females also expressed greater concern about being overweight.
- (p. 499) 5. Attitudes and preferences: Twelve universal sex differences in attitudes and preferences were found. Males express greater interest in physical science and technology, and they want to watch and participate in sports more often than do females. Females have a greater preference for marriage partners who are taller and wealthier than themselves, whereas males want mates who are shorter and younger than themselves. Females have greater interest in school, whereas males have more interest in sex.
- 6. Mental health: Twelve universal sex differences involved mental health issues, broadly defined. In this regard, alcoholism, learning disabilities, attention deficit disorder with hyperactivity, psychoticism, and autism are all more common in males. The cognitive/mental health traits that females exhibit more often are anorexia, bulimia, and panic attacks. Females are also more likely than males to blame themselves for any shortcomings, and they ruminate over unpleasant social experiences more.
- 7. Emotions and perceptions: The last category of universal sex differences involves females perceiving greater hazards in their environment, reporting greater feelings of stress, and crying more as adults. Males report feeling bored more.
Regarding emotions, readers
might suspect that there are other universal tendencies, such as the
tendency for women to be more depressed than men. There is in fact
considerable evidence supporting this particular conclusion (Hopcroft & Bradley, 2007). However, a few exceptions exist (Ellis et al., 2008,
p. 373). To give one of the most recent examples, data obtained from
China revealed that equal proportions of men and women self-reported
feeling depressed (Hopcroft & McLaughlin, 2012, p. 510).
Overall, it now appears safe
to say that many universal ASDCBs exist. If one uses the criteria we set
for confident conclusions in this regard, the number stands at 65. But
if somewhat more liberal criteria are used, the number could be in the
hundreds.
Of course, the search for
universal ASDCBs is not over. Findings from hundreds of new studies of
sex differences are published every year. No matter what criteria one
sets, it is possible that (a) more universal ASDCBs will be located in
the future and (b) exceptions to those already identified may be
eventually unearthed. With these provisos in mind, some rather
surprising evidence pertaining to ASDCBs is briefly described next. This
evidence has to do with the types of cultures in which one finds the greatest degree of sex differences in cognition and behavior.
Part 2: ASDCBs Over Time and Across Cultures
Societal efforts have been
made in Western cultures to treat the sexes more equitably for well over
a century. One of the earliest landmarks in this regard occurred in
1893 when New Zealand became the first country in the world to grant
women the right to vote,
(p. 500)
a right now afforded to all women living in democratic countries (Ramirez, Soysal, & Shanahan, 1997).
In many Western countries, particularly the United States, laws now guarantee women equal access to higher education (Klein et al., 2014), to sporting activities (Hargreaves, 2002; Milner & Braddock, 2016), and to employment opportunities (Rossilli, 2000).
Women’s rights activists continue to work toward even greater equality,
but undisputed progress has been made. For example, in Western
societies, most adult women are now in the paid labor force, a dramatic
increase over the past century (Durand, 2015).
Even more dramatic changes have occurred in terms of higher education.
At the start of the 20th century, roughly 90% of college graduates in
industrialized countries were men; by the early 1990s, well over half of
all college degrees were being awarded to women (Averett & Burton, 1996; Buchmann & DiPrete, 2006; Cho, 2007).
Given these trends, it is
worthwhile asking if they have been paralleled by any changes in ASDCBs.
For example, Have people’s attitudes toward sex equality shifted? Have
sex stereotypes changed? Or, have people’s self-perceptions of
themselves in masculine/feminine terms diminished? Although much of the
relevant data are limited to the United States, the results are quite
interesting. The following is a summary:
- US attitudes regarding sex equality: One study sought to determine if people in the United States are becoming more sympathetic to the idea that men and women should be treated more equally. To address this question, it compared responses to various questions about sex equality that were first administered in the early 1960s and then again in the mid-1990s (Thornton & Young-DeMarco, 2001). Findings indicated that substantial shifts have occurred. In particular, over the three decades involved, greater proportions of people of both sexes believed that men and women should be treated equally in interpersonal relations and in employment opportunities. From this investigation, it appears safe to infer that US attitudes regarding the desirability of treating the sexes equally have become more favorable in recent decades.
- US sex stereotypes: If attitudes toward treating males and females more equally have become more favorable, one might be led to believe that sex stereotypes have diminished. Sex stereotypes, of course, refer to the extent to which people believe that males and females behave differently regarding a wide range of traits. To address this question, one study compared sex stereotypes expressed by US respondents first in 1974 to similar respondents in 1997 nearly a quarter of a century later (Lueptow, Garovich-Szabo, & Lueptow, 2001). In both cases, respondents were given a list of behavior traits and asked to rate them as being either more typical of males (masculine) or of females (feminine, or not different regarding sex). Overall, this study concluded that nearly all of the stereotypes have remained virtually unchanged. The only exception involved a slight decrease in the extent to which females were stereotyped as exhibiting certain feminine traits, but there were no significant changes in the extent to which males were stereotyped as possessing masculine traits (see also Lueptow, 2005).
- (p. 501) US masculinity–femininity self-perceptions: Another investigation sought to assess trends in personality sex differences by meta-analyzing findings from studies that had all used a popular measure of masculinity–femininity, known as the Bem Sex Role Inventory (Twenge, 1997). All of the studies included in the meta-analysis were conducted in the United States predominantly among college students from the mid-1970s through the early 1990s. Analyses revealed no significant changes in the degree to which males considered themselves to be masculine or feminine over a wide variety of interests and preferences. Females had not changed their self-ratings in terms of possessing masculine interests and preferences, but women sampled in the 1990s did express somewhat more feminine interests and preferences than did women sampled in the 1970s. Thus, although serious validity issues have been raised regarding the Bem scale (Hoffman & Borders, 2001), Twenge’s meta-analysis suggests that despite all the changes that have occurred both culturally and legislatively in terms of more equal treatment of men and women, the extent to which US college students perceive themselves regarding masculine or feminine traits has changed very little.
Part 3: ASDCBs Across Cultures
E-mail communications and
computerized data management have made it possible for researchers
throughout the world to conduct large-scale cross-cultural studies. One
such study involved assembling responses from prior studies of more than
23,000 respondents residing on four different continents (i.e., Africa,
Asia, Europe, and North America). The goal was to search for varied sex
differences in personality traits (Costa, Terracciano, & McCrae, 2001).
In particular, the meta-study sought to determine if people living in
Western countries (i.e., those in Europe and North America) exhibited
stronger or weaker sex differences in personality traits compared to
people from predominantly non-Western countries. Results revealed that
across all four continents, similar sex differences existed in nearly
all of the personality traits measured. However, to the amazement of the
researchers, the degree of sex differences in personality traits
was more pronounced in the Western countries than in the predominantly
non-Western countries (p. 322). Thus, despite all the social and
legislative efforts made to promote sex equality in Western countries,
sex differences in personality traits were greater in the Western countries than in countries in which few such efforts have yet to be undertaken.
Click to view larger
Figure 23.1 A scatterplot of the relationship between the mean sex differences in overall personality traits reported by Schmitt et al. (2008) and the mean sex differences reported by Costa et al. (2001)
for the 25 countries sampled by both research teams. The dotted lines
represent 95% confidence around the fitted linear regression line.
Source: Schmitt et al. (2008, p. 176).
Subsequent work by Schmitt (2015)
involved measuring personality traits among respondents drawn from 26
different countries. It further reinforced the conclusion that the most
extreme average sex differences were among respondents drawn from the
most industrialized and affluent predominantly Western societies.
Similar conclusions about affluent Western societies exhibiting the
greatest sex differences have been reported not only for personality
traits (McCrae & Terracciano, 2005; Schmitt et al., 2016) but also for depression, for which females typically surpass males (Hopcroft & Bradley, 2007; Hopcroft & McLaughlin, 2012).
In the case of academic achievement, most studies have found that females outperform males at least through adolescence (Ellis et al., 2008,
pp. 278–279). A recent international study of more than 1 million
adolescents was undertaken to determine if there were fewer tendencies
for females to outperform males in predominantly Western
(p. 503)
egalitarian countries as opposed to countries in which
equality of the sexes is generally discouraged. It found no significant
differences in this regard (Stoet & Geary, 2015).
Overall, although Western
attitudes toward sex equality have become more prevalent in recent
decades, sex stereotypes and sex differences in ASDCBs (e.g.,
self-concepts and personality) have changed very little. Even more
surprising, when Western industrial societies are compared to
non-Western developing countries, sex differences in personality traits
appear to be more pronounced in the former than in the latter.
What in the world is going on? Perhaps theories of ASDCBs can shed light
on these rather curious findings.
Part 4: Theories of ASDCBs
Ideas on why males and
females seem to think and behave differently have been around for a long
time. Proposals began to solidify enough to be identifiable as
scientific theories much more recently. Basically, three theories with
distinct properties can be identified.
Social Role Theory
The concept of social roles
began to be used by social scientists in the 1940s. It refers to how
human behavior often seems to be heavily influenced by the training and
expectations one receives from others (e.g., parents, teachers, and
other influential persons) within a particular culture as though
people’s behavior is being scripted by others (Merton, 1968; Parsons, 1942). This perspective began to take the form of a theory of sex differences in behavior in the 1960s (Rosenberg & Sutton-Smith, 1968; Tulkin, Muller, & Conn, 1969).
Social role theory (also sometimes called sex role theory)
argues that all sex differences in behavior are learned through the
socialization process. Basically, each individual learns what is
culturally expected of men and women, and most then gradually conform to
those particular norms depending on their own sex (Bussey & Bandura, 1999; Kessler & McKenna, 1978).
To illustrate, one of the first things any expectant parent wants to
know about his or her baby is whether it is a boy or a girl. As soon as
one learns the answer, from birth onward, boys and girls are treated
differently on average, and it is this differential treatment as well as
a child’s understanding of how he or she is expected to behave that cause average sex differences in behavior to develop throughout life (Eagly, 2013; Eagly & Wood, 1999; Eagly, Wood, & Diekman, 2000; Ridgeway & Correll, 2004).
Currently, among the most prominent proponents of social role theory are Eagly and Wood (1999; see also Eagly, 2013).
They assert that were it not for learning and powerful socialization
processes, males and females would be all but identical in their
behavior. In their words, “extensive socialization is required to orient
boys and girls to function differently” (Wood & Eagly, 2002, p. 705). Another proponent summarized social role theory as follows (Rogers, 2005): “Men are expected to be ‘aggressive’ and unemotional,
(p. 504)
women to be sensitive, intuitive, etc. From a very
early age, they learn what is expected of them in terms of ‘feminine’ or
‘masculine’ personality, and this is heavily reinforced at puberty” (p.
11).
Social role theory reflects
what has been termed a “blank slate” perspective because it assumes that
males and females would behave the same if it were not for the
societies in which they live having different expectations of what is
“appropriate” behavior for males and females (Pinker, 2002,
pp. 337–371). In other words, social role theorists “expect gender
differences in personality to be smaller in cultures with more gender
egalitarianism” (Schmitt et al., 2016,
p. 1). It is worth keeping in mind that two surveys have both indicated
that social role theory is by far the most popular theory for
explaining sex differences in behavior, at least among sociologists (Horowitz, Yaworsky, & Kickham, 2014; Sanderson & Ellis, 1992).
Evolutionary Theory
Beginning in the 1970s, some social scientists began to move toward studying ASDCBs from an evolutionary perspective (Daly & Wilson, 1978; Simon, 1980). Since then, evolution-based proposals for explaining ASDCBs have expanded a great deal (Buss, 2012; Campbell, 2013; Geary, 2010; Hopcroft, 2016; Lippa, 2010; Mealey, 2000; Schmitt, 2015).
Without denying the role of learning or culture, proponents of this
perspective emphasize that biological and reproductive factors are even
more important.
The main elements in all
evolutionary explanations for ASDCBs can be summarized as follows:
Biologically, the purpose of life is simply to produce more life,
especially life resembling whatever organisms are currently living. In
sexually reproducing species, two individuals are required to make new
life: one male and one female. For males and females to attract one
another, each must exhibit certain traits. In highly evolved species
such as humans, the “right” combination of male and female traits for
attracting the opposite sex includes behavior as well as physical
characteristics.
To provide a simple
illustration of the previously discussed line of reasoning, imagine that
there are two groups of females in a human population. Group 1 prefers
mating with males who control a continual supply of food and other
resources and are willing to share them with their mates. Group 2 has no
interest in males with resources, preferring instead males who appear
to be young and attractive from a health standpoint. Which group of
females will pass their genes on at the highest rate? Group 2 would have
an advantage in the sense that young and health mates would be more
likely to produce healthy offspring. However, Group 1 females would
gravitate toward mates with resources to sustain them throughout each
pregnancy. Especially given the lengthy gestation periods for each human
pregnancy and the dependence that each offspring has on a stable supply
of resources, under most circumstances, the females in Group 1 would
probably out-reproduce those in Group 2.
Now pose the same question
for two groups of males. Again assume that the males in Group 1 prefer
females who control and share resources, whereas the males in Group 2
(p. 505)
are primarily drawn to females who appear youthful and
healthy. Keep in mind that because they do not gestate offspring, males
have a much higher reproductive ceiling than do females. So which group
of males would most likely have the most surviving offspring? By
choosing females who control many resources, the Group 1 males would be
drawn to women who are willing to spend considerable time working, which
would probably limit the time these women would devote to gestating
offspring. On the other hand, the Group 2 males who are most drawn to
females who are relatively young and attractive would be able to pass
their genes on at considerably higher rates, provided they (the males)
are willing to devote time to resource provisioning.
The preceding evolutionary
reasoning may seem almost too simple for its implications to be true in
reality. However, notice how scenarios match evidence that males
emphasize youthfulness and physical attractiveness more than females do
when choosing mates, whereas most females are more interested in mating
with males with the capacity to make a “decent living” (Conroy-Beam, Buss, Pham, & Shackelford, 2015; Zentner & Mitura, 2012).
It is impossible to prove that these sex differences in human mate
preferences are evolutionarily based, but the fact that there is
virtually no society in which these mating patterns do not exist (Ellis et al., 2008, pp. 441–444; Shackelford, Schmitt, & Buss, 2005) is at least consistent with such an explanation.
Also, notice how the
evolutionary arguments just presented can be extended to help explain
some other well-documented sex differences:
- 1. Compared to females, males are more likely to choose jobs based on how much money they can earn (Ellis et al., 2008, pp. 462–463).
- 2. On average, among full-time workers, males work longer hours (Ellis et al., 2008, p. 782).
- 3. In every society ever studied, mothers spend more time caring for their children than do fathers (Ellis et al., 2008, pp. 651–652).
- 4. Throughout the world, males express stronger desires to have multiple sex partners than is the case for females (Ellis et al., 2008, pp. 435–437; Schmitt, 2003).
The overall point being made
is that evolutionary reasoning can provide useful conceptual tools for
making sense of quite a few apparently universal ASDCBs. Of course,
social role theorists might explain these same sex differences by
arguing that each one reflects a “cultural script” of what males and
females should do. As discussed further in the following section, the
main problem with the “cultural script” hypothesis is that it implies
that very few, if any, universal ASDCBs should exist.
Evolutionary Neuroandrogenic Theory
It may be possible to
strengthen conventional evolutionary theory, at least in terms of
explaining ASDCBs, by combining it with evidence of how genes, hormones,
and the brains of males and females differ. Biologically, the only
things that survive indefinitely
(p. 506)
after an organism dies are the genes carried by its
descendants. Within a given species, these genes come in two forms, one
for males and the other for females. By and large, the collection of
genes for males and for females are extremely similar. The main
exception involves the so-called sex chromosomes, of which females carry two X chromosomes and males have just one X along with one Y chromosome.
In essence, female mammals (including humans) are the default sex, with males being just a variant on the female sex (Dennis, 2004; Woodson & Gorski, 2000).
Genes on the Y chromosome serve to effectively switch the would-be
female ovaries into becoming testes instead. Testes are special organs
for producing a sex hormone known as testosterone along with other so-called male sex hormones, collectively known as androgens.
Hormones are
biochemicals that are produced in one part of the body and then
transferred to other parts of the body (usually via the blood system)
where they have their primary effects. Although testosterone and other
androgens are produced mainly in the male testes, small quantities are
also produced in the female ovaries and in the adrenal glands of both
sexes. Studies have shown that bodily exposure to androgens has many
effects, including the promotion of muscle and bone tissue (Leonard et al., 2010), thereby explaining why males on average are stronger and taller than females (Ellis et al., 2008, pp. 15 and 30). However, it is the effects of androgens on the brain that are of greatest importance regarding ASDCBs.
Research has shown that
androgens alter the brain in many ways, including the size of various
parts of the brain, the biochemicals being released, and how the brain
actually functions (Baron-Cohen, 2004; Kimura, 1992; McHenry, Carrier, Hull, & Kabbaj, 2014).
These androgenic modifications occur both prenatally and
postpubertally, with the prenatal effects of androgens being the most
profound and irreversible (Auyeung, Lombardo, & Baron-Cohen, 2013; Baron-Cohen, 2004). As one would expect, many parts of male and female brains have been shown to differ on average, both structurally (Ellis et al., 2008, pp. 54–78) and functionally (Ellis et al., 2008, pp. 79–87).
To help explain universal
ASDCBs, I have proposed a theory that can also be considered merely an
extension of Darwinian evolutionary theory. Thus, it is called evolutionary neuroandrogenic (ENA) theory (Ellis, 2011a, 2011b).
The theory stipulates that androgens have evolved as the main
biochemicals responsible for masculinizing/defeminizing the brain of an
otherwise female mammal. In other words, ENA theory asserts that
androgens not only masculinized/defeminized the body as a whole (e.g.,
increased muscularity) but also masculinize/defeminize the brain
specifically. Because the brain is the direct controller of both thought
and behavior, ENA theory offers the following explanation for universal
ASDCBs: By androgenizing the brain, natural selection has tailored male
brains to exhibit thoughts and behavior that promote a male reproductive strategy and female brains to exhibit thoughts and behavior conducive to a female reproductive strategy. The nature of both strategies is the types of thinking and behavior that helps each sex pass on genes to future generations.
In more detailed terms, ENA
theory asserts that androgens have evolved the ability to not only
masculinize/defeminize the body as a whole (e.g., increased muscularity
and bone density) but also masculinize/defeminize the brain, thereby
impacting thought
(p. 507)
and behavior. The resulting sex differences in thought
and behavior must serve both sexes’ overall reproductive interests. More
precisely, as a result of male brains being more heavily androgenized,
they mainly produce masculine thoughts and behavior, most of which are
part of an overall male reproductive strategy. Female brains, on the
other hand, have evolved tendencies to retain feminine thoughts and
behavior, which are part of a predominantly female reproductive
strategy.
If the above reasoning is
correct, one can make the following deductions: Most universal ASDCBs
have evolved by natural selection and have been promoted by exposing the
brains of males to high (male-typical) levels of androgens. This means
that androgens are biochemicals naturally selected for modifying the
“normal” female brain into a male brain.
It is worth adding that the
nature of the evolved sex differences may not always be immediately
apparent. For example, nearly all studies have found males on average to
be more accurate than females when throwing objects such as balls or
darts at targets (Ellis et al., 2008,
p. 240). This ability may contribute little or nothing to male
reproductive success in today’s industrial societies. However, in the
past, it is likely to have enhanced male hunting ability, which in turn
allowed males to provide resources to mates who were gestating and
breast-feeding their offspring. Of course, the average number of
offspring they successfully rear would be the “reproductive payoff” for
the better hunting ability of these males (and for the females who chose
these males as mating partners).
ENA theory goes beyond conventional (Darwinian) evolutionary theory in the sense that it specifies how
neurohormonal factors has been naturally selected so as to produce
ASDCBs. This extra element in turn allows numerous testable hypotheses
to be derived from ENA theory about ASDCBs that conventional
evolutionary theory does not allow one to deduce.
To illustrate, consider the
field of criminology. Many proposals have been made in recent years that
evolutionary theory may help explain why males are more criminal than
females, especially regarding serious property and violent offenses (Buss, 2012; Daly & Wilson, 1990; Duntley & Shackelford, 2008; Ellis, 2005; Roach & Pease, 2013).
Most of these proposals hinge on the fact that males have a much higher
reproductive ceiling than do females (i.e., a male can have many more
offspring in a lifetime than can a female). Of course, for males to
capitalize on their higher reproductive ceiling, they need to have
numerous sex partners. But, as already noted, females generally prefer
males with resource-procuring abilities. To meet expectations in this
regard, males must usually compete with other males. Among the fastest
ways to obtain resources and thereby to attract potential mates is for
males to engage in thefts, burglaries, robberies, and embezzlements.
Additional criminal methods
males can employ to acquire mating opportunities involves the use of
physical force against prospective mates—that is, by committing rape or
sexual assault (Ellis, 2005).
Males can also effectively compete with rival males for resources and
mating opportunities by assaulting or even murdering these rivals (Buss, 2012, Daly & Wilson, 1990).
The bottom line is that
because males can reproduce much more prolifically than females, many
males appear to have evolved several “dirty tricks” (that nearly
(p. 508)
all governments seek to suppress with the criminal
justice system) to help pass their genes on to future generations. Of
course, these evolutionary arguments are difficult to directly test.
However, because ENA theory links its evolutionary arguments directly
with arguments about the effects of androgens on the brain, it provides
additional testable hypotheses about sex differences in offending. For
example, if ENA theory is true, criminals should have brains that are
more highly androgenized. In other words, although almost all males
should have higher androgen levels than females, criminal males should
have even higher androgen levels than males in general.
Recently, a colleague and I tested this line of reasoning using two separate samples, one from the United States (Hoskin & Ellis, 2015) and the other from both the United States and Malaysia (Ellis & Hoskin, 2015).
In both studies, we provided respondents with a checklist of delinquent
and criminal acts for them to self-report. To measure brain exposure to
prenatal androgens, we used a measure known as the 2D:4D ratio.
This measure simply involves the relative length of the second and
fourth digits (usually on the right hand). Basically, the longer the
fourth digit (ring finger) is compared to the second digit (pointing
finger), the greater the exposure to prenatal testosterone and possibly
other androgens (Manning, 2009).
Our findings were consistent
with what ENA theory predicts: Respondents with the lowest 2D:4D ratios
reported greater involvement in delinquency and crime than respondents
with the highest ratios. We even tested the hypothesis separately by sex
and found the same basic pattern: Both males and females with the
lowest 2D:4D ratios self-reported more crime compared to their
counterparts with relatively high 2D:4D ratios. This evidence, of
course, does not by itself prove ENA theory because the theory basically
makes the same predictions for all evolved traits that exhibit average
differences between males and females (Ellis, 2011a, 2011b).
Therefore, ENA theory provides a conceptual platform for theorizing
about all manner of ASDCBs with more ways of being disproven than is
true for conventional evolutionary theory.
Part 5: Theoretically Explaining Societal and Temporal Variations in ASDCBs
The last issue to be covered
in this chapter involves assessing each of the three theories just
identified—social role theory, conventional evolutionary theory, and ENA
theory—regarding their abilities to explain findings reviewed in Parts
1–3. In other words, which of these three theories can account for
findings about the apparently universal ASDCBs documented so far?
Regarding Part 1, both of the
evolutionary theories have an advantage over the social role theory.
This is because social role theory assumes that cultural learning is
largely responsible for ASDCBs. If this were true, one would not expect
to find very many, if
(p. 509)
any, universal ASDCBs. To give just a few examples, why
would alcoholism and interests in engineering be more common in men in
all known societies if these sex differences are the result of
culturally based learning? Similarly, one should be able to find
societies in which boys express greater liking of school and seek to be
more cooperative with others compared to females, but as of yet, such
sex differences have failed to materialize in any empirical study (Ellis, 2011a).
In the case of the two
evolutionary theories, both can explain the findings reviewed in Part 1
by simply noting that evolutionary forces have operated on human
populations in essentially the same way for thousands of years.
Therefore, if most ASDCBs are either directly or indirectly the result
of natural selection, one would expect to find many universal ASDCBs. It
is worth mentioning that ENA theory goes on to predict that the vast
majority of universal ASDCBs will be associated with differential brain
exposure to androgens, an implication that largely remains untested.
In the case of the findings
reported in Part 2, the picture is more mixed in terms of judging the
merits of the three theories. Recall that the main conclusions drawn
from the studies reviewed in Part 2 pertained to trends in the United
States. These trends were as follows:
- 1. Attitudes have become more accepting of equality between the sexes in recent decades.
- 2. Sex stereotypes have remained more or less stable during the past few decades.
- 3. Self-perceptions by men and women in terms of their being masculine, feminine, or somewhere in between have changed very little in recent decades.
Because social role theory
considers culturally based learning to be responsible for all ASDCBs, it
would probably explain attitudes toward sex equality also in terms of
cultural learning. Thus, as anti-discrimination laws began to be passes
in the United States especially in the 1960s, social role theorists
would expect public opinion to shift away from sex discrimination, which
it certainly has. Both of the evolutionary theories, however, are
essentially silent to the possibility of attitudinal changes regarding
sex equality, so they are weaker than social role theory in this regard.
Regarding the apparent
stability of sex stereotypes and self-perceptions concerning people’s
feelings of masculinity/femininity, both evolutionary theories would
probably have an edge over social role theory. This is because they
envision most ASDCBs as having evolved over thousands of years, making
them unlikely to change significantly over one or two generations.
Part 3 indicated that sex
differences in personality traits were more pronounced in most Western
industrial societies than in most non-Western developing countries. This
poses a serious challenge to all three theories of ASDCBs. Social role
theorists would be hard-pressed to explain why societies in which the
greatest efforts have been made toward sex equality would end up
exhibiting the most sex inequality, at least regarding personality. In
the case of the two evolutionary theories, they are largely silent
regarding any cross-country comparisons of sex differences in
personality.
(p. 510)
Because ENA theory has elements beyond what is found in
conventional evolutionary theory, it might be possible for researchers
to compare citizens from Western and non-Western societies in terms of
average androgen levels. If sex differences in androgen levels are
higher in countries with the greatest sex differences in personality, it
could begin to provide a theoretical basis for explaining
Western/non-Western patterns in this regard. Along these lines, a study
by Manning, Fink, and Trivers (2014)
compared countries in terms of their citizens’ average prenatal
androgen exposure and the percentage of elected officials who were
females and the percentage of the paid workforce who were females. The
study concluded that countries in which female exposure to prenatal
testosterone (as indicated by 2D:4D ratios) was high and in which male
exposure was low had the highest proportions of females in elective
offices and in the labor force. This study seems relevant to ASDCB
determination. However, notice that it implies that citizens of Western
societies have fewer average sex differences in exposure to
androgens than do citizens of non-Western societies. The studies
summarized in Part 3 by Costa et al. (2001) and Schmitt et al. (2008), on the other hand, lead one to conclude that Western societies have greater
average sex differences in personality than do non-Western societies.
These seeming inconsistencies call for more empirical scrutiny.
Conclusion
This chapter was divided into
five parts. Part 1 documented growing evidence of numerous universal
ASDCBs (average sex differences in cognition and behavior). In
particular, work by colleagues and myself led us to tentatively identify
65 such traits (Ellis, 2011a, 2011b; Ellis et al., 2008).
In Part 2, studies pertaining
to three questions about ASDCBs were explored. First, have people’s
attitudes toward sex equality changed, and if so, in what direction? The
answer is that these attitudes have changed. At least in the United
States, acceptance of women being educated and allowed to work in jobs
alongside men has grown considerably since the 1970s (Thornton & Young-DeMarco, 2001).
Second, have sex stereotypes
changed, and if so, how? The answer appears to be that sex stereotypes
have changed very little during the past few decades at least in the
United States. Specifically, people’s beliefs about how males and
females differ in terms of basic interests, personality, and behaviors
appear to have remained virtually the same in the 1990s as they were in
the 1970s (Lueptow, 2005; Lueptow et al., 2001).
Third, have there been
changes in men’s and women’s self-perceptions regarding their
masculinity/femininity? In other words, do the sexes today think of
themselves as just masculine, feminine, or somewhere in between, as was
true in their parent’s generation? The evidence suggests that the answer
is that little has changed, with the possible exception of contemporary
women having somewhat more feminine interests than those sampled in the
1970s (Twenge, 1997).
(p. 511)
The issue addressed in Part 3 had to do with making
cross-cultural comparisons regarding sex differences in personality.
Surprisingly, the evidence suggests that greater sex differences exist in most Western industrialized societies than in most non-Western developing societies (Costa et al., 2001; Hopcroft & Bradley, 2007; Hopcroft & McLaughlin 2012; Schmitt et al., 2016).
This finding seems counterintuitive because considerably more effort
has been made in most Western societies to encourage sex equality than
has been made in most non-Western societies.
Part 4 described the three
theories that have been proposed for explaining ASDCBs. The oldest one
to be proposed is social role theory (Eagly & Wood, 1999).
This theory asserts that males and females would be virtually identical
in how they think and behave if it were not for sex differences in
sociocultural training and expectations (Eagly et al., 2000). Surveys among sociologists indicate that it remains the most popular theory among social scientists (Horowitz et al., 2014; Sanderson & Ellis, 1992).
Beginning in approximately
the 1970s, Darwin’s theory of evolution began to be specifically applied
to the study of human ASDCBs (Hrdy, 1981; Wilson & Daly, 1978). Since then, numerous others have advocated an evolutionary approach to the study of ASDCBs (Archer, 1996; Geary, 2010; Hopcroft, 2016; Mealey, 2000).
An evolutionary perspective explains why males and females think and
behave differently based on how the sexes differ in their contributions
to the reproductive process. In other words, the rate at which humans
leave descendants (and therefore their genes) in future generations
depends heavily on males and females thinking and behaving differently.
Thus, whether operating through differential learning or some biological
process, the most reproductively successful males will exhibit thought
and behavior patterns than on average differ from those of the most
reproductively successful females.
I have proposed a version of evolutionary theory that specifically incorporates brain and hormonal concepts (Ellis, 2006, 2011a, 2011b).
This theory, called evolutionary neuroandrogenic (ENA) theory, is
specifically designed to explain average sex differences in cognition
and behavior. According to this theory, all mammals (including humans)
are essentially females. However, a special chromosome has evolved that
carries genes for making roughly half of these would-be females into
males instead. In essence, these genes operate by causing the would-be
female ovaries to develop into testes, special organs for producing
large quantities of a masculinizing hormone called testosterone (along
with other male hormones, called androgens). Androgens affect thought
and behavior by infiltrating the brain both prenatally and following
puberty. As a result of greater androgen exposure, males on average end
up thinking and behaving in ways that serve their reproductive
interests, whereas low androgen exposure in females causes them to think
and behave in ways that generally contribute to their reproductive
interests.
Finally, Part 5 addresses the
question of how well the three theories described in Part 4 can shed
light on the evidence summarized in Parts 1–3. Social role theory has
difficulty explaining why there are numerous universal ASDCBs as
discussed in Part 1. It also predicts that ASDCBs would weaken as
societies become more sex egalitarian, which Parts 2 and 3 indicate have
not happened.
(p. 512)
Because evolutionary theory assumes that most ASDCBs
have been naturally (or sexually) selected, it is able to account for
why large numbers of ASDCBs exist, as indicated in Part 1. Furthermore,
the evidence cited in Part 2 that people’s stereotypes about sex
differences and their self-concepts in terms of masculinity/femininity
have changed very little in recent decades is also understandable in an
evolutionary context. ENA theory, as an extended version of evolutionary
theory, goes on to hypothesize that androgenic effects on the brain
explain how ASDCBs have evolved. It remains to be seen if most
ASDCBs are the result of neuroandrogenic factors, but at least one
recent test of this hypothesis regarding sex differences in mate
preferences provided moderate support (Ellis & Ratnasingam, 2015).
The evidence that sex
differences in personality traits appear to be more pronounced in
Western industrial societies than in most non-Western developing
societies (Part 4) presents a conundrum for all three theories of
ASDCBs. It is especially devastating to social role theory, which is
based on the assumption that gender differences would be least prevalent
in cultures that foster the greatest degree of “gender equality” (Schmitt et al., 2016). The fact that most sociologists subscribe to this theory more than any other (Horowitz et al., 2014; Sanderson & Ellis, 1992) suggests that a sea change is in the offering for how social scientists think about cognitive and behavioral sex differences.
There seems to be only a few
ways to explain why the most sex egalitarian societies have the greatest
degree of sex differences in terms of personality traits. One
possibility is that more of the genes responsible for sex differences in
cognitive and behavioral traits have accumulated in Western populations
than in non-Western populations. If so, one would be likely to find
that sex differences in physical traits would also be more prevalent in
Western populations, a possibility for which I could find no evidence.
Another possibility is that
by being more lenient in allowing its citizens to express themselves in
sex-related terms, males in Western cultures may end up thinking and
behaving in more male-typical ways, and females in more female-typical
ways, than is typical of non-Western cultures. If this second line of
reasoning is true, it would turn traditional sex-role theorizing on its
head. In other words, social scientists who argue that one should not
stereotype or try to influence people’s behavior according to
“conventional sex roles” because it contributes to sex inequality are
mistaken. To the contrary, the effects of culturally prescribed sex
roles would actually be inhibiting the expression of sex
differences in thought and behavior. Thus, the more equitably males and
females are treated by their sociocultural surroundings, the more
different men and women will become.
In closing, I offer a
proposal for social scientists to consider and test during the ensuing
years. It is partly based on evidence that arranged marriages,
particularly among close relatives (usually first cousins), are
widespread both historically and even today in most developing countries
(Desai & Andrist, 2010; Jurdi & Saxena, 2003). Contemporary developed countries appear to be among the only cultures in which arranged consanguineal marriages are rare (Hatfield, Rapson, & Martel, 2007).
I propose that one of the
effects of freely marrying individuals from large pools of nonrelatives
is that this cultural practice allows the expression of genes for traits
to be
(p. 513)
maximized. This includes genes responsible for sexually
dimorphic cognitive and behavioral traits. If so, it is in societies in
which out-marrying is most common—that is, primarily Western industrial
countries—that one will find the expression of genes for masculine
traits in males and feminine traits in females to be the greatest.
Overall, it is clear that
research is still needed to identify ASDCBs and to understand the
factors responsible for them and for why they appear to be more
pronounced in some cultures than in others. Nevertheless, the
accumulation of ASDCB research so far is yielding tantalizing surprises
that could fundamentally challenge some of sociology’s more cherished
assumptions.
Acknowledgments
The comments provided by
Rosemary L. Hopcroft, Anthony Hoskin, Malini Ratnasingam, and David P.
Schmitt on drafts of this manuscript are greatly appreciated.
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