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Has the female body been designed
for orgasm during intercourse?

  Elisabeth Lloyd The Case of Female Orgasm The Case of Female Orgasm - Bias in the Science of Evolution.
by Elisabeth Lloyd
Harvard University Press 2005 hardback 311 pages

reviewed by Gert Korthof, 5 Jun 2005 (updated 27 Sep 2005)

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  Elisabeth Lloyd, biologist and philosopher of science, answers the question whether the female body has been designed for orgasm during intercourse with a firm 'NO'. Evolutionary biologists disagree.
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The facts...

  The primary data from the literature consistently show that roughly 25% of women have always, 75% have sometimes and 25% have rarely or never orgasm during intercourse (flat distribution). Unlike male orgasm, the female clitoris has no role in fertilisation. Female orgasm does not trigger ovulation. A women can become pregnant without orgasm. However, a man cannot fertilise a women without orgasm, because orgasm is the mechanism to deliver sperm.

Male nipples are constructed in the embryo at a time when the embryo is still sexless. Only thereafter, irreversible processes create a female or male embryo. Apparently, it is then too late to remove male nipples (proximate explanation: #4). Additionally, natural selection was unable too remove male nipples or to prevent their origin in males (ultimate explanation #4).

The clitoris and the penis have the same embryological source (#1). That source is present before an embryo has female or male commitment. During development the female clitoris neither grows nor degenerates #4). The existence (and potential uses) of male nipples can be compared with the presence and potential uses of the female clitoris.

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The theories...


If the female clitoris and female orgasm are not necessary for fertilisation, what are they doing? Any organ or behaviour that is not directly or indirectly helpful for reproduction is a problem for evolutionary biology. If something helps reproduction, it will be selected for. If something does not help reproduction, it will be selected against. Two main solutions for this problem are possible. The first is that there is a biological useful function, but we do not yet know it.

A structure that has been improved by natural selection for better performance of a particular task

A structure in the animal world that is not adapted for any function, but is an accidental and unselected consequence of something else
The second is that there is no useful function, but it is a by-product of another useful function (#8). Both solutions need to answer the same questions: Why is female orgasm during intercourse so variable in the human species? Why do only a small fraction of women have always orgasm during intercourse? Male orgasm is certainly adaptive, but is female orgasm an adaptation? Lloyd thoroughly examines 20 adaptionist hypotheses and one non-adaptionist hypothesis that try to explain this mystery. The majority of evolutionary biologists hold that the clitoris and female orgasm is an adaptation (see box), although, strangely, they do not have problems with the fact that male nipples are not adaptations. According to Lloyd evolutionary biologists have been unable to show convincingly the evolutionary advantage of female orgasm. One of the biggest merits of the book is that Lloyd shows that all the evidence presented for the 20 evolutionary accounts simply fail to support the theories. Theories are defended without good evidence or even are contradicted by the evidence. The female clitoris and female orgasm are the result of the peculiar way the external genitals of both sexes are created during embryological development. The by-product hypothesis (#9) says that female orgasm exists because natural selection selected males with orgasms. Selection on male orgasm is strong because male orgasm is the mechanism that delivers the sperm and secondly it is rewarding. The by-product hypothesis does not deny that the clitoris itself is adaptive in that it facilitates sexual excitement, although Lloyd does not dwell on the subject. She only claims that nobody ever showed a selective advantage of female orgasm. This by-product hypothesis has long time been ignored without good reason, and today is still rejected by the majority of evolutionary biologists. The claim of Lloyd's book is that evolutionists have an 'adaptionist bias'. Evolutionists assume that everything must have survival value, and try very hard to find a function. According to Lloyd, the by-product hypothesis gives the definitive explanation and there is no need for an adaptive explanation.
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Lloyd's position is unorthodox and admirable

  The by-product hypothesis triggers different feelings in different people. Lloyd's position is unexpected but admirable. In the first place the by-product hypothesis (the one Lloyd prefers) views female orgasm as a non-adaptive trait. This aspect of the hypothesis has the effect that women who never experience orgasm during intercourse are just as normal as women who always have orgasm during intercourse. The majority point of view in evolutionary biology is that female orgasm during intercourse is a meaningful evolutionary adaptation and not only an embryological fluke. A consequence of the majority view is that women without orgasm during intercourse are abnormal from an evolutionary point of view.
    In the second place, the by-product hypothesis is a non-adaptive explanation, but paradoxically depends on an adaptation in males. The reason is that female orgasm is developmentally derived from, and depends evolutionary on male orgasm, which is an evolutionary adaptation. This aspect of the by-product hypothesis triggers strong emotions in feminists. As a result women scientists show as much adaptionist bias as their male colleagues.
    In the third place, the by-product hypothesis has been invented by a man (Donald Symons) and has been rejected by most feminist scientists. Lloyd however, courageously rejects all adaptionist bias, including feminist adaptionist bias.
    Finally, the by-product hypothesis opens a new perspective on female homosexuality (not explored in the book).
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A few comments...

      Actually, it is not clear what the by-product hypothesis predicts. On the one hand it seems to predict disappearance of female intercourse-orgasm because: (1) every characteristic of an organism that is non-adaptive and does not contribute to reproductive success will eventually disappear (like eyes of cave animals), and (2) it can be concluded from the variation of intercourse-orgasm in the population that there is anatomical, or physiological or neurological variation which ultimately is based on genetic mutations. If there is no positive selection for the trait, mutations will accumulate, (3) generally negative mutations are more probable than positive mutations, so the trait will disintegrate and disappear ultimately.
    On the other hand, and this is what Lloyd claims, the by-product hypothesis predicts that intercourse-orgasm will continue to exist in the population as long as there is strong positive selection on male orgasms. However, if the clitoris with all its neurological pathways is an embryological copy of a well functioning penis, why is the clitoris not 100% functional in 100% of the females at 100% of the intercourses?
    It looks as if the by-product hypothesis depends on two contradictory ideas: a faithful copy and a non-faithful copy. The faithful copy is there to explain the existence of female orgasm in spite of the lack of any contribution to reproductive success. The non-faithful copy is supposed to explain the flat distribution in the female population. One cannot have a faithful copy and a non-faithful copy at the same time. Furthermore, if male orgasm is under selection for an optimum and consequently shows an optimum peak distribution, how can this explain a flat distribution in females?

    This brings me to the point that Lloyd emphasises the similarities of penis and clitoris (and this is correct, see also: #1), but ignores the differences in general. For example, the clitoris is very much smaller and has no urethra inside it. Why? What causes these differences? Why is the clitoris not smaller or bigger or completely absent? Why doesn't it have a urethra? Is this a just-so developmental story? In any case, Lloyd did not explain the specifics of the differences. The persistence of such specific differences in the human species cannot be explained by selection in males alone. Otherwise, females would have a penis in stead of a clitoris. One needs specific reasons why the clitoris has the properties it has. Similarities are probably best explained by developmental constraints and differences by natural selection acting on the adult body.
    The concept of by-product seems to be based on two contradictory ideas: that it is fixed and non-fixed. The developmental pathway of the clitoris and penis are linked so strongly that whatever happens in the male is reflected in the female. But at the other hand the developmental pathway is flexible enough to produce a completely different organ, with a completely different behaviour.

    My own solution is that female intercourse-orgasm is a moderately adaptive by-product and the effectiveness of manual stimulation is the real by-product in both sexes, because it has a zero contribution to reproduction. There is a gradual transition between clearly adaptive and completely non-adaptive structures. By-products and adaptations are not mutually exclusive. They operate in concert. Natural selection can be very weak or very strong. Male nipples and female clitoris are organs that are not strongly adaptive, but have some use for the individual. Male nipples are located more on the non-adaptive extreme of the scale, because they are not linked to reproduction. Female intercourse-orgasm is a more adaptive by-product than male nipples because it has a link to reproduction (intercourse) and is rewarding. It is just an extension of the rewarding effect of the other rewarding effects, which Lloyd claims are adaptive. So, male nipples are a bigger evolutionary puzzle than female intercourse-orgasm. Both are maintained in the population by the link with adaptive structures in the other sex and by weak positive selection. Lloyd writes: "No one has argued that the clitoris - as the primary source of sexual pleasure in females - does not contribute to reproductive success". Why would this rewarding effect not apply to intercourse-orgasm? Selection is weak because orgasm is not necessary for fertilisation and there are several other hot spots of sexual excitement in the female (the U-spot, the G-spot, the A-spot) which dilute the selection effect. That explains why the feature has not become fixed in the human species.

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Bias in the science of evolution?

  Although the explanation of adaptation by natural selection is central to Darwinism, Darwin himself recognised non-adaptive features in organisms. Therefore, there is no adaptionist bias in the science of evolution. The bias is in the scientists, not in the science.
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  This book is an eye-opener for those interested in the design of the human body, the evolutionary aspects of female sexuality, the nature of adaptations and the role of bias in scientific discussions. The discussion of these issues in a book for the general public is unique; I did not find any discussion of it in the evolution textbooks.
The by-product theory is an unsatisfactory developmental just-so story, but all selection theories have difficulties explaining the variability of female orgasm too. Please, could the real Designer disclose the design specifications of the female body? I have a few more questions about the design! (#7)


  1. The fact that penis and clitoris are embryological identical is uncontroversial. A dramatic proof of the common origin are intersex people called 'guevedoces'. They look superficially like girls at birth. Remarkably, they urinate through their clitoris. At puberty their clitoris has a sudden growth spurt as it quickly transforms into a normal penis. p.156 David Bainbridge (2005) Making Babies. Sigmond Freud already knew the anatomical homology of penis and clitoris. A very clear and interactive graphic about the development of the external genitalia can be found at: http://www.sickkids.ca/childphysiology/cpwp/Genital/genitaldevelopment.htm. (click on geneticals on the left and then click on genital formation.) This clearly shows the common origin of clitoris and penis.
  2. In the female fetus the Wolffian duct degenerates and in the male fetus the Mülleran duct degenerates. p.526-527 Scott Gilbert (2000) Developmental Biology, sixth edition.
  3. Jared Diamond (1997) Why is Sex Fun? The evolution of human sexuality, page 50. Remarkably, Diamond neither discusses orgasm in this book, nor in his The Third Chimpanzee !
  4. See for a very good description of proximate and ultimate explanations: John Alcock (2001) Animal Behavior, 7th edition, chapter 2.
  5. Definition of orgasm: "the explosive discharge of neuromuscular tension", page 21 of Lloyd's book.
  6. Falk HC, Hyman AB. (1971) Congenital absence of clitoris. A case report. Obstet Gynecol. 1971 Aug;38(2):269-71.
  7. For example, how could the monthly flow of blood from the female body possibly be an adaptation? What is the survival value of pubic hair? Why a few hairs on nipples? Why external testis in males?
  8. The idea of a by-product was first published by Stephen J. Gould and Richard Lewontin (1979) "The Spandrels of San Marco and the Panglossian paradigm: a critique of the adaptionist programme". "Its thesis is that many structures in the animal world are not adapted for any function, but, like the spandrels of San Marco, are accidental and unselected consequences of something else. Further, they argued, many adaptive explanations are "Just So Stories," unsupported by evidence" (JMS). (http://www.nybooks.com/articles/1703). "I think their paper had a healthy effect" says JMS.
  9. Lloyd now calls the by-product hypothesis the 'fantastic bonus' account [pers. comm.]

       Further Reading  
  • Mark Ridley (2004) Evolution, Third Edition, Chapter 10 is devoted to adaptive explanation. Recommended. Natural selection can explain in principle all known adaptations. Genetic, developmental and historic constraints may cause imperfect adaptation.
  • Louis Berman (2003) The Puzzle. Exploring the Evolutionary Puzzle of male homosexuality. Another by-product theory. review
  • Stephen Jay Gould (2002) The Structure of Evolutionary Theory, (review). On page 1262-1263 Gould states that "the clitoral site originated as a nonadaptive spandrel", but has no hostility to the idea that orgasm is potentially adaptive. He has essentially the same story as Lloyd, except two things. Firstly, he does not mention Lloyd. Remarkably, Lloyd wrote that she suggested the topic to Gould. Secondly, Gould omits the kind of evidence that is crucial for Lloyd's argument: the 25%never/50%sometimes/25%always orgasm. Gould does mention two joint articles with Lloyd but these are on different topics. However, see:
  • Stephen Jay Gould (1991) Male Nipples and Clitoral Ripples is chapter 8 in: Bully for Brontosaurus. Recommended reading. In this chapter Gould credits Lloyd [pers.comm. E.L.]
  • A review of The Case of Female Orgasm by Gail Vines NewScientist 14 May 2005.
  • Genes blamed for fickle female orgasm by Rowan Hooper, NewScientist.com 08 June 2005. This is the first study I know of that directly addresses the question whether there is a genetic basis for the variability of female orgasm. The fact that the study found a significant genetic component means at least that natural selection is able to select for the trait. "Comparing the results from identical and non-identical twins suggests that 34% of this variation in ability to orgasm during intercourse is genetic." [ 8 Jun 05]
  • Elisabeth Lloyd's views on the new heritability study of female orgasm (June 09, 2005) on this Philosophy of Biology site. [ 17 Aug 05]
  • Olivia P. Judson (2005) Anticlimax, Nature, 18 aug 2005, p.916 is a review of Lloyd's book. (Olivia Judson is the author of Dr. Tatiana's Sex Advice to all creation) [ 18 Aug 05]
  • Natalie Angier (1999) Woman. An Intimate Geography. Translated in Dutch as De vrouw. De waarheid over het vrouwelijk lichaam (1999) [ 4 Feb 2006 ]
  • Barry R. Komisaruk, Carlos Beyer-Flores and Beverly Whipple (2006) The Science of Orgasm Johns Hopkins University Press: 2006. 280 pp. Review: Nature: "Orgasms apparently alter pain perception and increase pain thresholds, and this link may explain bizarre reports of women having orgasms during childbirth."
  • Brendan P. Zietsch, Pekka Santtila (2011) 'Genetic analysis of orgasmic function in twins and siblings does not support the by-product theory of female orgasm, Animal Behaviour 82, 1097-1101 (2011)
  • Aria Pearson (2011) Evolutionary mystery of female orgasm deepens, New Scientist, 09 September 2011

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Copyright ©G. Korthof 2005 First published: 5 Jun 2005 Updated: 27 Sep 05 F.R.: 5 Nov 11