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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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Summary |
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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. | ||||
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.
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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... |
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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. 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. | ||||
Conclusion | ||||
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)
Further Reading
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Copyright ©G. Korthof 2005 | First published: 5 Jun 2005 | Updated: 27 Sep 05 F.R.: 5 Nov 11 |