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The Case of the Female Orgasm: Bias in the Science of Evolution

Book Reviews 103
Do loving spouses care how many diapers they change
or who stays home with the children, or whether they
go to the ballet or the opera, or where they locate? Do
loving spouses experience conflict between their own
professional goals and those of their spouses? Might they
still be genuinely loving spouses if they do care? In my
view, the answers are yes, yes, and yes. A good marriage
need not represent a ‘union’ in which the circumstances
of justice are repealed. It may represent an intimate
partnership between autonomous individuals who do and
should have interests, goals, and aspirations that can
conflict. (p. 272)
Wertheimer’s analysis clearly demonstrates a solid
understanding of biology, psychology, law, and philos-
ophy. His approach is balanced and he takes pains
to present arguments from a variety of perspectives,
citing philosophical and evolutionary theory, legal cases,
feminist perspectives, etc. He contrasts sexual with
nonsexual issues regarding consideration of principles
of valid consent, such as sales contracts, robbery, ad-
vertising, threats of murder, medical procedures, and
This is not always easy reading, as the author’s
arguments are often quite detailed, contrasting as many as
five theoretical alternatives at a time. However, following
his logic is often captivating, especially considering his
balanced approach, his open appreciation of others who
may have found flaws or omissions in his thinking, and
the sprinkling of dry but tasteful humor. For some of us,
his conclusions will appear to be self-evident, at least in
certain areas, but we will now have the benefit of his
detailed analysis. For others, this volume may encourage
a reconsideration of attitudes and biases in these often
emotional areas of human life and behavior. The book
will be useful to anyone—attorney, psychologist, psy-
chotherapist, political scientist, philosopher—who values
a comprehensive, scholarly discussion of this important
Plaut, S. M. (1995). Informed consent for sex between health profes-
sional and patient or client. Journal of Sex Education and Therapy,
21, 129–131.
Wertheimer, A. (1996). Exploitation. Princeton, NJ: Princeton Univer-
sity Press.
The Case of the Female Orgasm: Bias in the Science
of Evolution. By Elisabeth A. Lloyd.HarvardUni-
versity Press, Cambridge, Massachusetts, 2005, 311
pp., $27.95.
Reviewed by David A. Puts, Ph.D.1
Lloyd argues that female orgasm is not an adaptation,
that it did not contribute to the reproductive success
of ancestral females, and, therefore, was not designed
to solve any particular reproductive problems faced by
ancestral females. Rather, Lloyd adopts Symons’s (1979)
hypothesis that female orgasm is like the male nipple—
non-functional and merely a developmental byproduct of
natural selection for a functional version of the trait in
the opposite sex. Males have nipples because they share
some of their development with females, in whom the trait
is an adaptation. Lloyd argues that females have orgasms
because they share some of their development with males,
in whom orgasm is an adaptation.
The book is generally well-written and accessible to
the lay reader. In its eight chapters, Lloyd systematically
reviews and critiques each of the 21 hypotheses so far
proposed for the evolution of orgasm in women. The thesis
is that various biases, including adaptationist and sexist
biases, have led to the uncritical acceptance of adaptive
explanations for female orgasm, when none is adequately
supported by evidence according to rigorous scientific
standards. This book has the merits that it will probably
encourage more research into the poorly understood
phenomenon of female orgasm, and researchers in this
area will likely be made more aware of their potential
biases. However, because of the overall polemical tone and
the sometimes narrow focus on possible shortcomings of
adaptive hypotheses, it does not serve as a comprehensive
introduction to evolutionary explanations for female
orgasm. And to those well-versed in evolutionary theory
and evolutionary explanations for female orgasm, this
book will probably be somewhat unconvincing, leaving
one with the impression that, if proponents of adaptive
explanations sometimes speak beyond their data, the
byproduct account is no more satisfying. Of course, Lloyd
would contend that these readers suffer from the same
biases as those she argues against. But at least one adaptive
hypothesis for female orgasm has reasonable support, and
Lloyd’s arguments have weaknesses, which are outlined
1Neuroscience Program, Michigan State University, East Lansing,
Michigan 48824; e-mail:
104 Book Reviews
Perhaps the most significant problem in this book
involves defining what evidence would be required to
settle the issue of whether female orgasm is an adaptation
or a byproduct. In Chapter 1, Lloyd cites West-Eberhard’s
(1992) definition of an adaptation: a character for which
“there is some evidence that it has evolved (been modified
during its evolutionary history) in specific ways to make
it more effective in the performance of [a particular
task], and that the change has occurred due to the
increased fitness that results” (West-Eberhard, p. 13).
Most evolutionists would agree almost completely, but
many would change the word results to resulted. This
seemingly minor change can be important. Organisms
possess a particular adaptation because it contributed to
the reproductive success of their ancestors, not because
it currently contributes to reproduction. There is no point
in debating semantics—which definition of adaptation is
“correct.” But the central question of Lloyd’s book is why,
evolutionarily, females experience orgasm. And Lloyd
incorrectly assumes that an adaptive answer depends
on female orgasm contributing to current reproductive
This focus on natural selection in current populations
unfortunately pervades the book. This is first seen clearly
in Chapter 1, where Lloyd summarizes what is required to
demonstrate that a trait is an adaptation: “First, it should
be shown that individual or geographic variations in a
trait have a genetic basis....Second, the trait should be
shown to influence reproductive success....[T]hird...a
mechanistic account explaining the links between the trait
and reproductive success in the wild should be elucidated.
These are, in fact, requirements to show that natural
selection is currently operating on a character, not to
show that selection has shaped the character over the
evolutionary history of the species. For natural selection
to have shaped a trait in the past, it is indeed necessary
for there to have been genetic variation associated with
variation in the trait. And variation in the trait must have
led to variation in reproductive success. Demonstrating
either of these currently might bolster the argument
that they existed in past generations, but their current
demonstration is unnecessary.
So what is required to show that a trait is an
adaptation? This can be a difficult task because we
cannot go back in time to measure the operation of
natural selection on a trait. According to Williams (1966),
complex structural organization can suggest that a trait
is an adaptation. Evidence that it serves a presumed
function “with sufficient precision, economy, efficiency rule out pure chance as an adequate explanation”
(p. 10) also helps distinguish an adaptation from a
byproduct. Essentially, an adaptation looks as though
it was designed for a particular function. And this
function must have clear benefits to reproductive success.
Lloyd discusses neither complexity nor the appearance
of functional design as evidence of adaptation. However,
Lloyd spends considerable time in Chapters 1 and 6
bringing home the important point that not all beneficial
traits are adaptations. In Chapter 1, Lloyd gives Darwin’s
example of the sutures of the mammalian skull, which
allow the skull to deform as it passes through the birth
canal. This benefit suggests that sutures are adaptations
to the problem of getting a large head through a relatively
small birth canal. However, sutures are shared with birds
and reptiles, which hatch from eggs. Thus, skull sutures
probably existed ancestrally before this benefit could be
realized, so they cannot be adaptations for this function.
On the other hand, evidence that a trait has been modified
over evolutionary history to serve a particular function can
help demonstrate that it is indeed an adaptation. For ex-
ample, the skin of female placental mammals has clearly
been modified in the formation of mammary glands and
A final method of establishing that a trait is an
adaptation for a hypothesized function is cross-species
comparison. If an adaptive hypothesis about a trait in
one species is correct, then other species possessing
similar traits should have experienced similar adaptive
problems over their evolution. For example, a hypothesis
that hovering flight in ruby-throated hummingbirds is
an adaptation to feeding on flowers would predict other
species with hovering flight to feed on flowers. However,
this comparison can be confounded by close evolutionary
relationships. Because closely related species share traits
due simply to inheritance from a common ancestor, other
hummingbird species with hovering flight should not be
used as evidence. Instead, hummingbird species that have
lost hovering flight could be investigated to see if they
do not feed on flowers. And species in which hovering
flight has evolved independently, such as some bats and
insects, could be examined. Although Lloyd does not
describe this approach to testing adaptive hypotheses, it is
worth bearing in mind when considering the cross-species
evidence discussed below.
To review, an adaptation can be recognized if it has
a complex structure that appears to have been designed
to perform some function that increased reproductive
success during the trait’s evolution, and if there is evidence
that it has been modified over its evolution to perform this
function efficiently. Additional evidence about a trait’s
potential adaptive function can be obtained by examining
closely related species in which the trait is absent and
Book Reviews 105
distantly related species in which the trait is present to
see if they lack or share, respectively, the hypothetical
selection pressure.
Although much of this book is devoted to discussing
what constitutes an adaptation, Lloyd is less explicit
about the kinds of evidence that would identify a trait
as a byproduct. Lloyd is clear about the most important
characteristic: a byproduct shares a common develop-
mental origin with an adaptation. Lloyd gives Symons’
(1979) example of the male nipple. As discussed above,
nipples are clearly adaptations in females but are probably
possessed by males only because males share some of their
development with females.
But shared development with an adaptation is not suf-
ficient evidence to conclude that a trait is a byproduct. For
example, the plumage of peahens and peacocks are devel-
opmentally related, but both are probably adaptations—
the former for avoiding predation, the latter for attracting
mates. To conclude that a trait is a byproduct, additional
evidence is needed. Whereas signs that a trait has been
modified for a function suggest an adaptation, the apparent
lack of design for efficient function indicates that the trait
may be a byproduct. However, it should be appreciated
that apparent lack of design may reflect only the present
state of knowledge, and future research may reveal a
convincing adaptive explanation. Finally, byproducts may
appear reduced, rudimentary, or vestigial.
These features are apparent in male nipples. Lloyd
notes that male nipples do not normally deliver milk
except under extraordinary hormonal conditions and thus
probably have not evolved for this function, but does
not mention the other obvious difference: males’ nipples
are smaller. Given the importance of the concept of
evolutionary byproducts in this book, it is surprising
that only the example of the male nipple is given. Let
us explore another example– the copulatory system of
leopard geckos.
As in other lizards, male leopard geckos possess
paired, bilateral copulatory organs called hemipenes
(Holmes, Putz, Crews, & Wade, 2005). Each hemipenis
is controlled by its own set of muscles, and either
hemipenis may be used during copulation. Interestingly,
adult female leopard geckos also possess hemipenes.
Female hemipenes are much smaller than males’ (less
than a tenth the volume), as are the associated muscles.
Female hemipenes do not appear to be connected with
vasa deferentia and, under normal conditions, female
hemipenes do not evert. There is no known function
for these structures in female leopard geckos. However,
female leopard geckos remain partially responsive to
androgens in adulthood, and androgen treatment increases
the size of this copulatory system as well as enabling
females to evert their hemipenes.
What lessons can we take away from these examples
of developmental byproducts? First, byproducts are devel-
opmentally related to clear adaptations in the opposite sex.
Second, byproducts do not appear to have been modified
over their evolution to provide function efficiently. Finally,
byproducts are reduced compared to the corresponding
adaptations in the opposite sex. They appear vestigial.
These facts suggest that the adaptations of one sex would
impair the sex bearing their byproducts, perhaps simply
because the adaptations would not compensate for their
costs of production and maintenance in the opposite sex.
Equipped with the ability to recognize adaptations
and byproducts, we are nearly ready to discuss Lloyd’s
analyses of evolutionary hypotheses about female orgasm.
But first we must agree on the trait that we are attempting
to explain. Here lies a problem. Lloyd defines female
orgasm by uterine contractions and other physiological
correlates to the exclusion of psychological aspects, such
as pleasurable sensations.
This definition is problematic for several reasons.
First, when women report on orgasm, they are almost cer-
tainly referring to the pleasurable, psychological aspects,
not the physiological ones. Because the psychological
aspects are the most salient to the experience of orgasm,
an evolutionary hypothesis that considers why uterine
contractions occur but does not explain the intense
pleasure will be unsatisfying. Second, considering both
physiological and psychological aspects of female orgasm
is likely to contribute to a better understanding of why
female orgasm evolved. This would be true if female
orgasm was a byproduct and both aspects appeared
vestigial. It would also be true if female orgasm was an
adaptation. Indeed, psychological and physiological as-
pects might have different functions. Consider the case of
male orgasm. The physiological aspect of male orgasm—
ejaculation—has the clear function of transmitting sperm
to the female’s reproductive tract. The pleasurable sen-
sations associated with male orgasm, on the other hand,
are unnecessary for transmitting sperm but may function
to reinforce copulatory behavior. Because Lloyd does not
consider the psychological aspect of orgasm, she misses
this distinction, asserting that “orgasm and ejaculation are
strongly selected in a sperm-delivery system”
106 Book Reviews
(p. 110). Finally, the exclusion of the psychological
aspects of female orgasm is problematic because some
of the adaptive hypotheses that Lloyd criticizes depend
on them, as we shall see.
One of the reasons that so many researchers have
proposed adaptive hypotheses for female orgasm is
probably that the intense pleasure seems likely to have
affected copulatory patterns over human evolution. And
because copulation is tied to reproduction, it would appear
that orgasm must have influenced female reproductive
success. Even assuming heritability of female orgasm
over human evolution, this putative connection between
female orgasm and reproductive success does not mean
that female orgasm is an adaptation. Recall that beneficial
traits are not rightly considered adaptations unless there
is evidence that they have been modified over their evo-
lution for efficiency of function. Moreover, a connection
between female orgasm and reproductive success does
not imply that the former increased the latter. If female
orgasm is a byproduct of male orgasm, it is possible that
orgasm decreased reproductive success in females.
Nevertheless, Lloyd questions the apparent connec-
tion between orgasm and reproductive success in females.
Of course, a current connection between female orgasm
and reproductive success is unnecessary for female or-
gasm to be an adaptation. But if female orgasm is an
adaptation, it must have increased reproduction during
its evolution. Whereas male orgasm affects reproductive
success through its association with copulation, Lloyd
contends that female orgasm is only tenuously related
to sexual intercourse. She uses three lines of evidence
to make this point: First, most women report not having
orgasms with every act of sexual intercourse. Second,
women vary considerably in their reported rates of
orgasm, with a small percentage reporting never having
had an orgasm from intercourse. Finally, masturbation in
women, and both masturbation and homosexual interac-
tions in non-human primate females, appear more likely to
elicit orgasm than does heterosexual intercourse. In sum,
copulation only sometimes leads to orgasm, and other
behaviors may be at least as effective as copulation at
eliciting orgasm.
The fact that masturbation and other non-copulatory
sexual behaviors are effective at eliciting female orgasm
might suggest that female orgasm is not an adaptive
response to copulation. However, as noted above, male
orgasm is almost certainly an adaptive response to copu-
lation. And orgasms from masturbation and other sources
are at least as common in males as they are in females.
It seems plausible that, in both sexes, orgasm has been
favored as a response to particular sexual behaviors, but
the mechanisms that have evolved for these functions can
be triggered by other stimuli. Similarly, the rods and cones
of the retina have been selected for their responsiveness to
light, yet they can be stimulated by pressure from a finger
on a closed eyelid, a response for which they were not
What about the fact that copulation only sometimes
causes female orgasm? This would be problematic if adap-
tive hypotheses assumed female orgasm was a response
to copulation generally. It would appear inefficient. But
it is not a difficulty if female orgasm is hypothesized to
be an adaptive response to intercourse only in certain
contexts. This could explain why orgasm does not al-
ways accompany copulation in females; females do not
always copulate under the same conditions. It could also
explain some between-female variation in orgasm rates—
females differ in their sexual experiences. It seems that
female orgasm could have affected reproductive success
through its relationship with heterosexual intercourse. But
a convincing evolutionary hypothesis must explain the
irregularity with which sexual intercourse elicits female
orgasm. Several evolutionary hypotheses for female or-
gasm make predictions regarding these irregularities. Let
us consider the predictions pair-bond, sperm competition,
and byproduct hypotheses.
Pair-bond hypotheses (Chapter 3) postulate that
social bonds between males and females have been
adaptive and that female orgasm has helped cement
these bonds. Thus, pair-bond hypotheses predict that
female orgasm will be more common from within-pair
copulations than from extra-pair copulations. The sperm
competition hypothesis (Chapter 7) makes a different set
of predictions. Sperm competition occurs when the sperm
of different males compete to fertilize the eggs of a single
female. Although Lloyd questions this, sperm competition
has probably imposed significant selection on humans
over their evolution. Sperm competition favors large testes
and rapid evolution of proteins associated with ejaculate
production, both of which are greater in humans than in
gorillas, in which sperm competition is low. Rates of extra-
pair sex indicate moderate sperm competition, as do rates
of extra-pair paternity, which are only around 2% across
human populations but 10% in traditional populations
(Simmons, Firman, Rhodes, & Peters, 2004). Because
sperm competition occurs when multiple males mate with
the same female, it can select for female mechanisms
that influence the probability of fertilization by particular
males. According to the sperm competition hypothesis,
female orgasm is an adaptation to promote conception
Book Reviews 107
from males of high genetic quality (Baker & Bellis, 1993;
Smith, 1984; Thornhill, Gangestad, & Comer, 1995). A
variety of research suggests that females may recruit
genes outside of their long-term mateships (Gangestad
& Simpson, 2000). The sperm-competition hypothesis
thus predicts that female orgasm is likelier not only from
intercourse with good-genes males, but also during extra-
pair copulation. Finally, the byproduct hypothesis predicts
no relationship between partner type and orgasm.
Regrettably, Lloyd misses the opportunity to com-
pare these competing hypotheses in relation to this
critical set of predictions. In fact, evidence regarding
these predictions best supports the sperm competition
hypothesis. Baker and Bellis (1993) presented evidence
that females were more likely to experience orgasms
from extra-pair copulation than from intra-pair copulation
(Fig. 7, p. 902), evidence that Lloyd does not discuss in
her consideration of this study. Thornhill et al. (1995)
also find support for the sperm competition hypothesis.
They examined orgasm rates of women in 86 heterosexual
couples in relation to a composite measure of the overall
bilateral symmetry of their male partners. Because bodily
symmetry is a putative marker of genetic quality, Thornhill
et al. predicted (and found) higher rates of orgasm in
females mated to symmetrical men. Lloyd criticized
this study because it “involved no extra-pair matings
whatsoever, and thus no sperm competition” (p. 211).
However, this is not problematic for the sperm competition
hypothesis. The sperm competition hypothesis predicts
increased rates of orgasm with good-genes males; it does
not require these males to be extra-pair males. According
to this hypothesis, rates of female orgasm should be higher
for extra-pair than for intra-pair copulation only because
females, when they are sexually unfaithful, tend to obtain
extra-pair sex from good genes males.
The major criticism leveled by Lloyd against the
sperm competition hypothesis, however, regards one of
the mechanisms by which female orgasm putatively
promotes fertilization by good genes males. According
to the sperm-competition hypothesis, the uterine contrac-
tions associated with orgasm capture sperm. Fox, Wolff,
and Baker (1970) measured a drop in uterine pressure
following copulatory orgasm. This pressure drop may be
caused by oxytocin release. Oxytocin levels rise following
orgasm (Blaicher et al., 1999) and Wildt, Kissler, Licht,
and Becker (1998) showed that treatment with this
hormone caused uterine contractions lowered uterine
pressure and rapid movement of a semen-like substance
into the uterus. Uterine contractions also transport sperm
in other mammals, including rats, dogs, and cows (Singer,
1973). And, in humans, Baker and Bellis (1993) found
that female orgasms within 1 min before and 45 min after
ejaculation were associated with higher sperm retention
than was no orgasm or orgasms at other times.
Lloyd noted that two studies failed to find movement
of semen-like substances through the cervix following
orgasm. However, both studies used a cap placed over
the cervix, which Fox et al. (1970) contended may have
prevented flow, one study used a fluid more viscous than
semen, and the other involved masturbatory orgasms,
which Singer and Singer (1972) argued led to fewer uter-
ine contractions. Lloyd also points out that uterine con-
tractions occur constantly, and oxytocin may be released
during sexual simulation without orgasm, so orgasm may
be unnecessary for sperm-capturing uterine contractions.
But, as discussed above, both uterine contractions and
oxytocin release have been found to increase following or-
gasm, as have uterine suction and sperm retention. Finally,
Lloyd questioned the Baker and Bellis (1993) study on
statistical grounds, pointing out such potential drawbacks
as small, non-normal samples, unjustified use of different
subsample sizes, and inappropriate statistical tests. Vary-
ing subsample sizes probably reflect incomplete responses
by some subjects (e.g., seven couples were not willing to
collect sperm flow-backs), and Baker and Bellis justified
their statistics in a previous paper. Although many of
Lloyd’s points may be valid, there is at least very sugges-
tive evidence that female orgasm increases sperm uptake.
Evidence regarding the so-called physiological
aspects of female orgasm need not stand on its own. What
about the psychological aspects? An adaptive hypothesis
would posit that pleasurable sensations function to
reward the behavior that caused them. Smith (1984)
postulated that the psychological aspects of orgasm cause
females to bond with the males with whom they had
orgasm. Thornhill et al. (1995) found no evidence that
women’s orgasm rates with their male partner affected
their reported love for or commitment to him. However,
the pleasurable feeling of orgasm may increase females’
likelihood of copulating again with the same male, even
if it does not increase emotional commitment to him.
And given that a single act of unprotected intercourse,
even at peak fertility in the cycle, is unlikely to result
in fertilization, this repeated copulation would seem to
facilitate fertilization by particular males, thus supporting
the sperm competition hypothesis.
In Chapter 5, Lloyd correctly posits that, “If the
byproduct account is right, then those species in which the
sexual organs and tissues are most intensely selected in
the males would also be expected to have highly sexual—
and perhaps orgasmic—females” (p. 130). But in which
species will males be, as Lloyd puts it, “highly sexed”?
Lloyd presents evidence for female orgasm in stumptail,
rhesus, and Japanese macaques, and in chimpanzees
108 Book Reviews
and bonobos—all species with multi-male groups where
sperm competition is expected to be high and thus males
are expected to be highly sexual. But, importantly, the
sperm competition hypothesis makes the same predictions
about the distribution of female orgasm across species.
For example, the sperm competition hypothesis predicts
the absence of female orgasm in gorillas, where sperm
competition is essentially nonexistent, because there has
been no selection for females to influence fertilization
by particular males. And the byproduct hypothesis makes
this prediction because there has been no selection on
male gorillas to produce frequent or large ejaculates. Thus,
the cross-species evidence that Lloyd presents in support
of the byproduct hypothesis is equally supportive of the
sperm-competition hypothesis.
Of the evolutionary hypotheses proposed thus far,
the sperm competition hypothesis best explains both the
physiological and the psychological aspects of female or-
gasm, as well as predicting its variability and cross-species
distribution. In general, female orgasm seems like an
adaptation. Multiple lines of evidence suggest that female
orgasm has been designed for the function of sire choice
in species where the sperm of multiple males compete for
fertilization in a single female, although this interpretation
should be made tentatively at present. One might construe
the variability of orgasm within and between females as
an indication that orgasm is reduced in females—evidence
that it is a byproduct of selection for orgasm in males. But
this would be like predicting that only some males would
have nipples, or that males would have nipples only some
of the time. If anything, female orgasm appears elaborated
by selection, modified in its pattern of response to
sociosexual stimuli and in its physiological manifestation.
Many of Lloyd’s criticisms may be valid, but no
study is perfect, and too many would have to be wrong for
female orgasm not to look like an adaptation. Lloyd claims
that these studies are flawed because they were motivated
by various biases, including sexism and adaptationism.
It strikes the reader that the accusation of sexism may
be more of a defensive response to past accusations
(discussed in Chapter 5) that the viewpoint espoused in
this book is antifeminist. Lloyd is probably right that the
concept of adaptation is sometimes used capriciously, de-
spite Williams’ (1966) admonition that it is “a special and
onerous concept that should be used only where it is really
necessary” (p. 4). However, no sexist views or adapta-
tionist agendas have prevented researchers from thinking
that nipples in human males and hemipenes in leopard
gecko females are truly byproducts. In contrast, female
orgasm simply has the appearance of an adaptation. It
has the complexity that is the hallmark of an adaptation.
Williams (1966) noted that biologists recognized the
lateral line system of fishes as an adaptation before they
knew its function. After several decades of research on
female orgasm, we may be closing in on its function.
Baker, R. R., & Bellis, M. A. (1993). Human sperm competition:
Ejaculate manipulation by female and a function for the female
orgasm. Animal Behaviour,46, 887–909.
Blaicher, W., Gruber, D., Biegelmayer, C., Blaicher, A. M., Knogler, W.,
& Huber, J. C. (1999). The role of oxytocin in relation to female
sexual arousal. Gynecologic and Obstetric Investigation,47, 125–
Fox, C. A., Wolff, H. S., & Baker, J. A. (1970). Measurement of intra-
vaginal and intra-uterine pressures during human coitus by radio-
telemetry. Journal of Reproduction and Fertility,24, 243–251.
Gangestad, S. W., & Simpson, J. A. (2000). On the evolutionary
psychology of human mating: trade-offs and strategic pluralism.
Behavioral and Brain Sciences,23, 573–587.
Holmes, M. M., Putz, O., Crews, D., & Wade, J. (2005). Normally
occurring intersexuality and testosterone induced plasticity in
the copulatory system of adult leopard geckos. Hormones and
Behavior,47, 439–445.
Simmons, L. W., Firman, R. C., Rhodes, G., & Peters, M. (2004).
Human sperm competition: Testis size, sperm production and
rates of extrapair copulations. Animal Behaviour,68, 297–
Singer, I. (1973). The goal of human sexuality. New York: W. W. Norton.
Singer, J., & Singer, I. (1972). Types of female orgasm. Journal of Sex
Research,8, 255–267.
Smith, R. L. (1984). Human sperm competition. In R. L. Smith (Ed.),
Sperm competition and the evolution of animal mating systems (pp.
601–660). London: Academic Press.
Thornhill, R., Gangestad, S. W., & Comer, R. (1995). Human female
orgasm and mate fluctuating asymmetry. Animal Behaviour,50,
Wildt, L., Kissler, S., Licht, P., & Becker, W. (1998). Sperm transport in
the human female genital tract and its modulation by oxytocin as
assessed by hysterosalpingoscintigraphy, hysterotonography, elec-
trohysterography and Doppler sonography. Human Reproduction
Update,4, 655–666.
Williams, G. C. (1966). Adaptation and natural selection. Princeton, NJ:
Princeton University Press.
... Results: The sperm flowback (simulated) was measured using a technique that can be used in a home setting. There was a significant difference in simulant retention between the orgasm (M = 4.08, SD = 0.17) and Barash, 2005; Judson, 2005; Pound & Daly, 2000; Puts, 2006), it is still an open question whether female orgasm has been sculpted by natural selection to somehow in- 45 crease the dispersal of genes in future generations or whether it exists only as a by-product of some other adaptation. In this latter case, the most promising candidate would be the strong selection on the sensitivity of the male homologue of the clitoris Á namely the penis 50 ...
Full-text available
Background Human female orgasm is a vexed question in the field while there is credible evidence of cryptic female choice that has many hallmarks of orgasm in other species. Our initial goal was to produce a proof of concept for allowing females to study an aspect of infertility in a home setting, specifically by aligning the study of human infertility and increased fertility with the study of other mammalian fertility. In the latter case - the realm of oxytocin-mediated sperm retention mechanisms seems to be at work in terms of ultimate function (differential sperm retention) while the proximate function (rapid transport or cervical tenting) remains unresolved. Method A repeated measures design using an easily taught technique in a natural setting was used. Participants were a small (n=6), non-representative sample of females. The introduction of a sperm-simulant combined with an orgasm-producing technique using a vibrator/home massager and other easily supplied materials. Results The sperm flowback (simulated) was measured using a technique that can be used in a home setting. There was a significant difference in simulant retention between the orgasm (M=4.08, SD=0.17) and non-orgasm (M=3.30, SD=0.22) conditions; t (5)=7.02, p=0.001. Cohen's d=3.97, effect size r=0.89. This indicates a medium to small effect size. Conclusions This method could allow females to test an aspect of sexual response that has been linked to lowered fertility in a home setting with minimal training. It needs to be replicated with a larger sample size.
... Facultative adaptations should exhibit even greater variation. We have considered these arguments and others more fully elsewhere (Puts, 2006a(Puts, , 2006b(Puts, , 2007Puts & Dawood, 2006). ...
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Debate surrounds whether women's orgasm is an adaptation or by-product of orgasm in men. We clarify what evidence would decide this debate and review evidence that female orgasm is an adaptation for promoting fertilization by men of high genetic quality. Female orgasm does not appear vestigial as by-products do. Rather, cross-species data suggest that female orgasm depends on the quality of a female's mate and evolves where females copulate polyandrously. Sex differences in human orgasm frequency mirror sex differences in choosiness over mates, and orgasm frequency tracks conception risk across the cycle, another indicator of a sire choice function. Manipulations of orgasm-related hormones and brain regions in humans and nonhuman mammals indicate that female orgasm promotes conception. We review evidence of men's concern over female orgasm in order to gauge paternity certainty, and evidence that women feign orgasm in order to maintain male investment.
... The evolutionary basis of the human female orgasm has long been intensely debated, and the intensity has increased in recent years (e.g. Judson 2005;Lloyd 2005;Puts & Dawood 2006;Wallen 2006;Amundson 2008;Lynch 2008;Wallen & Lloyd 2008;Brody et al. 2011;Zietsch & Santtila 2011Puts et al. 2012b;Wallen et al. 2012). The debate centres on whether female orgasm has an evolutionarily adaptive function and, if so, what that function is. ...
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The evolutionary basis of women's orgasm is unknown, but the most favoured theory involves putative physiological processes that accompany orgasm and increase the likelihood of fertilization during intercourse. In a sample of over 8000 female twins and siblings, we show a substantial genetic basis to both orgasm rate and number of offspring. While there was a very weak but significant phenotypic correlation between the two variables, there was no corresponding genetic correlation, suggesting the involvement of environmental confounders. Controlling for relationship length and frequency of sexual intercourse eliminated the significant phenotypic correlation between orgasm rate and number of offspring, which suggests no substantive causal relationship between orgasm and fertility. These results cast doubt on the predominant functional theory of female orgasm.
... Whether or not female orgasm serves an adaptive purpose has become a controversial topic (Alcock, 1980(Alcock, , 1987Barash, 1977Barash, , 2005Barash and Lipton, 2009;Beach, 1974;Eibl-Eibesfeldt, 1975;Gould, 1987;Hamburg, 1978;Judson, 2005;Morris, 1967;Puts and Dawood, 2006;Puts, 2006aPuts, , 2006bSymons, 1979). Some scholars insist that female orgasm serves no evolutionary function (Lloyd, 2005;Wallen, 2006Wallen, , 2007, while others believe it may serve one or more adaptive purposes (Baker and Bellis, 1993;Costa and Brody, 2007;Meston et al., 2004;Puts et al., 2012b;Shackelford et al., 2000;Singh et al., 1998;Smith, 1984;Thornhill et al., 1995;Wildt et al., 1998). ...
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Male and female sexual experiences differ considerably, particularly with regards to orgasm. Research into the female orgasm tends to follow one of two lines of reasoning: the by-product explanation or the adaptation explanation. The by-product explanation posits that the female orgasm is a functionless by-product of women’s early developmental similarity with men. By contrast, the adaptation explanation hypothesizes that female orgasm is an adaptation in its own, separate right. Supporters of the by-product explanation of female orgasm contend that because female orgasm is more difficult to induce than orgasm in men, is harder to produce via sexual intercourse than through masturbation, and is not necessary for reproduction, that it has not been designed via sexual selection. Supporters of the adaptation explanation of female orgasm, however, believe that female orgasm serves to increase fitness through one or more functions, such as through rewarding sexual behaviors, increasing pair bonds, augmenting the likelihood of conception, and/or working as a mate- or sire-selection mechanism. Here, the current literature on women’s orgasmic experience and evidence in favor of both competing explanations are reviewed. It is concluded that a by-product explanation may not provide an adequate summation of the findings, although definite proof in favor of the adaptive design of female orgasm is lacking, and that female orgasm is an important, unique experience that is worthy of continued attention from researchers.
... (Where traits count as functional when they contribute to the life and well-being of the organism.) Zietsch & Santtila cite philosopher and historian of science Ron Amundson, who argues that 'the orgasmic potentials of siblings are correlated even when the siblings are of different sex' (Amundson 2008, page 444). Zietsch & Santtila interpret this claim as the assumption that physiological function follows morphology. ...
Highlights ► We contest Zietsch & Santtila's (2011, Animal Behaviour, 82, 1097–1101) conclusions for the evolution of female orgasm. ► Zietsch & Santtila used inappropriate comparisons of different orgasmic properties. ► Zietsch & Santtila's analyses relied on linking correlated morphology with correlated function. ► Lack of correlation fully expected under by-product view. ► Zietsch & Santtila's findings are irrelevant to the by-product account for female orgasm.
... Alcock 1987;Gould 1987a, b;Sherman 1989;Mitchell 1992;Baker & Bellis 1993;Alcock & Sherman 1994;Thornhill et al. 1995;Hrdy 1996;Thornhill & Gangestad 1996;Alcock 1998), partly because it became the fulcrum of a broader theoretical dispute between so-called 'adaptationists' and 'pluralists', those purportedly biased towards adaptive or nonadaptive explanations for biological phenomena, respectively. The heat of this debate has recently intensified (Barash 2005;Judson 2005;Milam et al. 2006;Puts & Dawood 2006;Wallen 2006;Amundson 2008;Barash & Lipton 2009) after the 2005 publication of a provocative book by Elizabeth Lloyd, titled The Case of the Female Orgasm: Bias in the Science of Evolution (Lloyd 2005). In the book, Lloyd first comprehensively reviewed around 20 previously advanced theories regarding possible adaptive functions of the human female orgasm. ...
The evolutionary basis of human female orgasm has been subject to furious scientific debate, which has recently intensified. Many adaptive explanations have been proposed, invoking functions from pair bonding and mate selection to sucking up sperm, but these have been attacked as being based on flawed logic and/or evidence. The popular alternative theory is that female orgasm is not adaptive and is only evolutionarily maintained as a by-product of ongoing selection on the male orgasm-ejaculation system. This theory has not been adequately tested. We tested one of its central tenets: that selection pressure on the male orgasm is partially transmitted to the female via a positive cross-sex correlation in orgasmic function (susceptibility to orgasm in response to sexual stimulation). Using questionnaire data from over 10 000 Finnish twins and siblings, we found significant genetic variation in both male and female orgasmic function, but no significant correlation between opposite-sex twins and siblings. This suggests that different genetic factors underlie male and female orgasmic function and that selection pressures on male orgasmic function do not act substantively on female orgasmic function. These results challenge the by-product theory of female orgasm.
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Background: The evolution of the female orgasm in humans and its role in romantic relationships is poorly understood. Whereas the male orgasm is inherently linked to reproduction, the female orgasm is not linked to obvious reproductive or survival benefits. It also occurs less consistently during penetrative sex than does the male orgasm. Mate-choice hypotheses posit that the wide variation in female orgasm frequency reflects a discriminatory mechanism designed to select high-quality mates. Objective: We aimed to determine (1) whether women report that their orgasm frequency varies between partners, (2) whether this variation reflects mates' personal characteristics, and (3) whether this variation reflects own and partner sexual behaviour during intercourse. Design: We collected survey data from 103 women who rated (1) the extent to which their orgasm frequency varied between partners, (2) the characteristics of previous sexual partners who induced high-orgasm frequency and those who induced low-orgasm frequency, and (3) the specific behaviours during sex with those partners. This is the first study to test within-woman variation in orgasm and partner traits. Results: Overall, women reported variation in their orgasm rates with different partners. Partners who induced high-orgasm rates were rated as more humorous, creative, warm, faithful, and better smelling than partners who induced low-orgasm rates, and also engaged in greater efforts to induce partner orgasm. Conclusions: Some assumptions and predictions of mate-choice hypotheses of female orgasm were supported, while other aspects of our findings provide reasons to remain sceptical.
According to Evolutionary Psychology, what are now almost universally regarded as attractive features of the face and body, and certain mate recruitment strategies, conferred strong survival benefits to humans in prehistoric times, and still play an important role in our sex lives today. While there are over a hundred books and over two thousand articles covering these subjects, the recommended readings that follow each section of this article may provide science librarians with a more manageable way to familiarize themselves with the principal findings in the field thus far. Selections were based on the featured works being favorably reviewed, heavily cited, or highly current, and may be useful for collection development.
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Venus figurines such as the famous Willendorf Venus provide a possible window into the reproductive preferences of ancestral humans. These figurines cover a period of about 20000 years of human history and have been found across ice-age Europe. There are a number of unknowns about such figurines. For example, they may be votive offerings, idealisations, or have some as-yet, unguessed-at function. Ancient figurines typically display body types considered obese by modern standards of medicine and aesthetics. While some have averred that such figurines show a marked change in human body preferences over thousands of years it is possible that this has been an artifact of particular approaches to measure such figurines. Measuring a fuller extent of the markers of fat deposition seems to support a case for arguing that male preferences have broadly tracked fertility markers over ancestral time. The waist-to-hip ratio is arguably a more important fertility marker than obesity per se and a 0.7 ratio has been found cross-culturally and in this sample. It is likely that such preferences have been further calibrated by local ecological variations for example as regards food supply but these calibrations would not have a great impact on proportionality preferences. Great caution must be taken in reading too much into such a limited sample
Introduction: Women describe at least two types of orgasms: clitoral and vaginal. However, the differences, if any, are a matter of controversy. In order to clarify the functional anatomy of this sexual pleasure, most frequently achieved through clitoral stimulation, we used sonography with the aim of visualizing the movements of the clitorourethrovaginal (CUV) complex both during external, direct stimulation of the clitoris and during vaginal stimulation. Method: The ultrasounds were performed in three healthy volunteers with the General Electric® Voluson® sonography system (General Electric Healthcare, Vélizy, France), using a 12-MHz flat probe and a vaginal probe. We used functional sonography of the stimulated clitoris either during manual self-stimulation of the external clitoris or during vaginal penetration with a wet tampon. Main outcome measures: Functional and anatomic description, based on bidimensional ultrasounds, of the clitoris and CUV complex, as well as color Doppler signal indicating speed of venous blood flow, during arousal obtained by external or internal stimulation. Results: The sagittal scans obtained during external stimulation and vaginal penetration demonstrated that the root of the clitoris is not involved with external clitoral stimulation. In contrast, during vaginal stimulation, because of the movements and displacements, the whole CUV complex and the clitoral roots in particular are involved, showing functional differences depending on the type of stimulation. The color signal indicating flow speed in the veins mirrored the anatomical changes. Conclusions: Despite a common assumption that there is only one type of female orgasm, we may infer, on the basis of our findings, that the different reported perceptions from these two types of stimulation can be explained by the different parts of the clitoris (external and internal) and CUV complex that are involved.
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Behavioural ecologists view monogamy as a subtle mixture of conflict and cooperation between the sexes. In part, conflict and cooperation is cryptic, taking place within the female’s reproductive tract. In this paper the cryptic interaction for humans was analysed using data from both a nationwide survey and counts of sperm inseminated into, and ejected by, females. On average, 35% of sperm were ejected by the female within 30 min of insemination. The occurrence and timing of female orgasm in relation to copulation and male ejaculation influenced the number of sperm retained at both the current and next copulation. Orgasms that climaxed at any time between 1 min before the male ejaculated up to 45 min after led to a high level of sperm retention. Lack of climax or a climax more than 1 min before the male ejaculated led to a low level of sperm retention. Sperm from one copulation appeared to hinder the retention of sperm at the next copulation for up to 8 days. The efficiency of the block declined with time after copulation but was fixed at its current level by an inter-copulatory orgasm which thus reduced sperm retention at the next copulation. Inter-copulatory orgasms are either spontaneous ( = nocturnal) or induced by self-masturbation or stimulation by a partner. It is argued that orgasms generate a blow-suck mechanism that takes the contents of the upper vagina into the cervix. These contents include sperm and seminal fluid if present; acidic vaginal fluids if not. Inter-copulatory orgasms will therefore lower the pH of the cervical mucus and either kill or reduce the mobility of any sperm that attempt to penetrate from reservoirs in the cervical crypts. Intercopulatory orgasms may also serve an antibiotic function. Copulatory and inter-copulatory orgasms endow females with considerable flexibility in their manipulation of inseminates. The data suggest that, in
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The most popular current explanation of rape holds that rapists are seeking power, control, violence, and/or domination instead of sex. After reviewing the history of this explanation, this paper examines the evidence that has been used to demonstrate that rapists are not sexually motivated. Twelve specific arguments are examined in light of existing data on rape. All twelve of the arguments are found to be either logically unsound, based on inaccurate definitions, untestable, or inconsistent with the actual behavior of rapists. The implications of these findings are discussed.
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In species with internal female fertilization, males risk both lowered paternity probability and investment in rival gametes if their mates have sexual contact with other males. Females of such species do not risk lowered maternity probability through partner infidelity, but they do risk the diversion of their mates' commitment and resources to rival females. Three studies tested the hypothesis that sex differences in jealousy emerged in humans as solutions to the respective adaptive problems faced by each sex. In Study 1, men and women selected which event would upset them more—a partner's sexual infidelity or emotional infidelity. Study 2 recorded physiological responses (heart rate, electrodermal response, corrugator supercilii contraction) while subjects imagined separately the two types of partner infidelity. Study 3 tested the effect of being in a committed sexual relationship on the activation of jealousy. All studies showed large sex differences, confirming hypothesized sex linkages in jealousy activation.
The controversy about clitoral versus vaginal orgasms was discussed in Chapter 10. In this article, the Singers offer a new typology of orgasm, which tries to integrate recent physiological research with women’s subjective experience of orgasm. While the authors’ typology has not gained widespread acceptance, this article is valuable for its careful description of the various subjective and physiological components of orgasm. The authors also make the point that description of what orgasm is can cause distress in women who discover that their orgasm does not meet some criteria. Orgasms are indeed different for different women, and for the same women on different occasions.
In this longitudinal study of college women, nine risk characteristics assessed prior to the start of college were examined in the effort to identify predictors of sexual victimization in college dating. A total of 100 women were followed for 32 months, with information about personal history, behaviors, and attitudes collected at Time 1 and information about subsequent sexual victimization collected at Time 2. Although four risk factors were significantly associated with victimization, a logistic regression analysis revealed that the best prediction model contained only two variables: Precollege sexual victimization in dating was positively correlated with college victimization, and sexual conservatism was negatively correlated with college victimization. Discussion focused on the needs for improved sex education for teenagers, prevention programs aimed at the precollege level, and increased research and clinical attention to the phenomenon of revictimization.
Recent investigations of risk factors for adult sexual assault have focused on a varietyof behavioral and cognitive variables, including victim risk-taking behaviors. In this study, cognitive appraisals of riskyactivities, behavioral intentions to engage in risk-taking behaviors, and alcohol use were examined in relation to future involvement in risk-taking behaviors and the incidence of sexual assault in a sample of college women. At Time 1, 50 (26%) participants reported a historyof sexual victimization and at Time 2, 16 (12.7%) reported new sexual victimizations. Discriminant function analysis indicated that alcohol use and expected involvement in risky activities at Time 1 were associated with new sexual victimizations at Time 2. Hierarchical regression analysis revealed that alcohol use and expected involvement in risky activities at Time 1 were predictive of frequencyof involvement in riskyse xual activities at Time 2. The implication of these findings for future research is discussed.
Intra-vaginal and intra-uterine pressure changes during human coitus were monitored by the use of a pressure-sensitive radiopill. Pressure was found to be negative in the vagina during intromission and male orgasm but became positive during female orgasm. In the uterus, the pressure changes were minimal during male orgasm but increased markedly during female orgasm to a positive pressure of 40 cm H2O, followed by a sharp fall after orgasm to a negative pressure of 26 cm H2O. The reliability of these results is discussed in relation to their possible significance in the pattern of sperm transport, and it is suggested that the final negative pressure following female orgasm may effect an `insuck' of the cervical mucus with its entrapped spermatozoa.