Re: Evolution and Sexuality

From: Harnad, Stevan (
Date: Sat Mar 04 1995 - 20:58:43 GMT

> From: "Bethan Barnes" <>
> Date: Fri, 3 Mar 1995 15:54:34 GMT
> I was wondering after the discussion in yesterday's lecture about the
> ultimate aim of sex being reproduction, where does Darwin stand with
> regard to the paedophile? Clearly the paedophile cannot hope to
> reproduce with a pre pubescent child, so surely the ultimate aim in
> this instance is pleasure.

Remember my alert about not mixing up the proximal and the ultimate?
The ultimate aim of sexuality is reproduction; its proximal aim is
pleasure. In this respect, the paedophile example is the same as the
homosexual example I mentioned in class, and the Darwinian explanation
is similar in both cases.

Whenever you have an evolutionary "cue" (such as the size of the eyes,
for example), it is always possible to create an exaggerated
"superstimulus" out of it, one that satisfies the proximal detectors of
the cue, but at the expense of the ultimate causes that first shaped
them. The so-called "cute" cues -- huge eyes, big head in relation to
the body -- elicit the "oh isn't it cute" reaction, and the reaction
can be bigger for unnatural eye and head sizes that are actually
monsters than it is for real biological proportions. You can create an
artificial superstimulus for a stickle-back fish that it will prefer to
court over real members of its species by just exaggerating certain
features in the direction of an existing preference.

Remember the example I gave of children's selective appetite for sweets
and fat, which was adaptive in our Environment of Evolutionary
Adaptedness, where sugar and fat were rare, yet essential, but is now
merely an exaggerated preference for something that's not so good for
you? It used to be adaptive. Now, it's mildly maladaptive, but with
modern dentistry and dieting, it's not killing off those who have the
preference, so it's just there.

The story with paedophilia may be similar (at least
adult-male/female- child paedophilia): As you see in the Buss and
Kenrick/Keefe articles, human males have a tendency to prefer SOMEWHAT
younger mates, for Darwinian reasons. Just crank that up into a
"superstimulus" and you see where it might yield.

But because paedophilia is much rarer than addiction to sweets, there is
probably more to it than just a superstimulus effect. Many paedophiles
are probably sociopaths (see the Mealey article); and there is also the
fact that, because the Darwinian mechanism of "neotony" (also called
"paedogenesis," the prolonging of earlier developmental and even
embryological stages in the service of new adaptations) is such a
prominent feature of the human species, perhaps that leaves open the
possibility of becoming fixated on a cue that was "intended" for an
earlier stage of development (remember the ducklings that imprinted on
Lorenz -- and then wanted to mate only with human beings at maturity?).

Homosexuality is harder to explain. If it were just an exaggerated
bisexual preference, it could be explained as early fixation on
ambiguous androgynous cues, again a developmental fixation, and
then a superstimulus amplification effect. But if there really is a
subpopulation of the human species that is genetically disposed toward
exclusive homosexuality, then it, like left-handedness, is harder to
explain adaptively (though people have tried in both cases, producing
what I, at least, find rather silly "Just-So" stories; I've added
some Abstracts after this message).

> Also, with regard to this issue, many paedophiles claim maladaptive
> learning (or in other words the fact that they were abused themselves)
> as the reason that they themselves abuse. Does this mean that
> maladaptive learning can overide the genetic desire to reproduce?

Yes, of course it can. That's just the proximal over-riding the
ultimate (as in children's appetite for sweets). But there's always
something that has puzzled me about the transgenerational abuse
theories of paedophilia: They don't make sense in terms of the gender
statistics. It is my understanding that the vast majority of abusers
are males, and the majority of victims are younger females. How
could proportions like that pass themselves on from generation to
generation? You would have to predict some sort of oscillation, with
males abusing females for one generation, then females abusing
(males?), then vice versa again. If most abuse were male on male, then
the theory would have made sense, but as it is, there needs to be more
to it that just the abused-abuser hypothesis.

Here are some Abstracts of papers that have evolutionary theories about
about homosexuality, paedophilia and left-handedness.

Chrs, Stevan

   Dickemann, Mildred.
   Reproductive strategies and gender construction: An evolutionary view of
   homosexualities. Homosexuality, Which Homosexuality? Conference (1987,
   Amsterdam, Netherlands).
   Journal of Homosexuality, 1993, v24 (n3-4):55-71.
   ABSTRACT: Examined whether the historical occurrence of various forms of
   homosexuality (HM) and bisexuality can be explained as part of the
   management of reproduction in response to environmental conditions (ECs).
   It is believed that explanations for the occurrence and forms of HM
   appealing to genetics are biologically indefensible and historically
   inadequate. However, Darwinian behavioral theory, specifically the life
   history theory, provides an explanatory framework. An individual's life
   course consists of behaviors coerced by parents and chosen by the
   individual in response to ECs, forming a coherent reproductive strategy.
   In the process, alternate male and female genders are explained, and the
   normative male bisexuality of classical Athens and modern
   Mediterranean/Latin societies is elucidated. The rise of modern HM in
   industrial nations results from the demographic transition to low
   mortality and low fertility.
   Mihalik, Gary J.
   From anthropology : Homosexuality, stigma, and biocultural evolution.
   Special Section: Stigma and homosexuality.
   Journal of Gay & Lesbian Psychotherapy, 1991, v1 (n4):15-29.
   ABSTRACT: Discusses stigmatization of homosexuals from the standpoint of
   neuropsychological functioning. One model of the processing of perceptual
   and cognitive information uses descriptive axes composed of antonyms; this
   is the basis of the "us-them" dichotomy that is an integral part of the
   process of stigmatization. The development of the neocortex has made
   greater cognitive and behavioral flexibility possible, releasing humans
   from the rigid stimulus-response behavioral paradigm. There is a strong
   positive correlation between psychological androgyny and the flexibility,
   adaptability, and complexity of mental function. Homosexuals are more
   psychologically androgynous than nonhomosexuals and are likely to
   contribute significantly to the process of cultural evolution. Hampering
   such evolution through continued stigmatization of homosexuals is
   detrimental to the species.
   Weinrich, James D.
   Human reproductive strategy. I: Environmental predictability and
   reproductive strategy; effects of social class and race. II: Homosexuality
   and non-reproduction; some evolutionary models.
   Dissertation Abstracts International, 1977 Apr, v37 (n10-B):5339.
   Wilson, Glenn D., ed.
   Variant sexuality: Research and theory. Johns Hopkins University Press;
   Baltimore, MD, US, 1987.
   ABSTRACT: (from the book) The study of sexual behaviour is a subject that
   always attracts wide interest, but which is characterised more by
   sensational stories in the media than by scientific analysis. With variant
   sexuality and sexual deviation that is even more true. Some deviations,
   such as fetishes, may be trivial or at times amusing, but others may lead
   to horrific crimes. Although family forms of sexual behaviour such as
   homosexuality are now more widely discussed, others such as paedophilia
   are still largely taboo, and others may require clinical treatment....
   This book presents contributions from major international authorities
   reviewing major themes in variant sexuality, and presenting new research.
   For example, there is evidence of neurological factors being identifiable
   in exhibitionists, who can be distinguished from normals on the basis of
   EEG responses to mental tasks. Genetic and evolutionary arguments are
   presented for the preponderance of paraphilia in males. Freudian and
   psychoanalytic theories are shown to have limited scientific explanatory
   power. These and other topics are reviewed in a book that should interest
   psychologists, biologists and psychiatrists in particular, as well as
   others fascinated by the social, behavioural and biological aspects of
   List of contributors.
   Deviation and variation. Alex Comfort. (Chapter record available).
   Genetic and hormonal factors in human sexuality: Evolutionary and
   developmental perspectives. Raymond E. Goodman. (Chapter record
   Cerebral aspects of sexual deviation. Pierre Flor-Henry. (Chapter record
   An ethological approach to sexual deviation. Glenn D. Wilson. (Chapter
   record available).
   Logical models of variant sexuality. Vaclav Pinkava. (Chapter record
   The phylogenetics of fetishism. Arthur W. Epstein. (Chapter record
   Sexual deviation: Psychoanalytic research and theory. Paul Kline. (Chapter
   record available).
   A cross-cultural perspective on homosexuality, transvestism and
   trans-sexualism. Frederick L. Whitam. (Chapter record available).
   The courtship disorders. Ron Langevin and Reuben A. Lang. (Chapter record
   The sadomasochistic contract. Christopher C. Gosselin. (Chapter record
   ABSTRACT: (from the cover) (The authors) analyze current research on asymmetry
   Springer, Sally P.; Deutsch, Georg.
   Left brain, right brain (4th ed.). W. H. Freeman & Co, Publishers; New
   York, NY, US, 1993.
   ABSTRACT: (from the cover) (The authors) analyze current research on asymmetry
   in brain-damaged, split-brain, and normal Subjects, and explore its
   implications for human behavior.
   (from the publicity materials) (This book presents) information on:
   (left-handedness) and mortality; the role of hormones on sex differences
   in cognition; "handedness" in non-human primates; how the concept of
   "hemisphericity" has been applied and misapplied; "natural" split brains
   or agenesis of the corpus callosum; developmental disabilities and
   asymmetry; the promise and limitations of neuroimaging; the newest views
   on memory and perception; hemispheric differences and emotion; issues of
   mind-brain relationships (and) left brain/right brain programs in business
   management and creativity seminars.
   Early evidence from the clinic: The discovery of asymmetry.
   The human split brain: Surgical separation of the hemispheres.
   Asymmetries in the normal brain.
   Measuring the brain and its activity: Physiological correlates of
   The puzzle of the left-hander.
   Further evidence from the clinic: Aphasia, apraxia, agnosia.
   Further insights from the clinic: Neglect, amnesia, music, and emotion.
   Sex and asymmetry.
   Phylogeny and ontogeny: The evolution and development of asymmetry.
   Asymmetry's role in developmental disabilities and psychiatric illness.
   Hemisphericity, education, and altered states.
   Concluding hypotheses and speculations.
   Appendix: Functional neuroanatomy: A brief review.
   McManus, I. C.; Bryden, M. P.
   Handedness on Tristan da Cunha: The genetic consequences of social
   isolation. International Journal of Psychology, 1993 Dec, v28 (n6):831-843.
   ABSTRACT: Examined the suggestion by K. A. Provins (see PA, Vol 78:514) that
   the apparently low incidence of left-handedness on the island of Tristan
   da Cunha (TDC) is the result of social pressures such as deference to
   authority and group conformity, and that "any genetic factor determining
   left-handedness must be very weak." The authors used 10,825 Monte Carlo
   simulations of the growth of the population of TDC from 1827 to 1961, to
   show that if the original population was randomly selected from a large
   population with a typical gene-frequency, then a combination of founder
   effects, genetic drift, and evolutionary bottlenecks can readily explain
   the low incidence of left-handedness that was found. Indeed, in 15% of the
   simulations the C allele, which is postulated to be responsible for
   left-handedness, has disappeared, resulting in a population with no
   left-handers. The data from TDC are therefore compatible with a genetic
   model of left-handedness. (French abstract)
   Hopkins, W. D.; Bard, K. A.; Jones, A.; Bales, S. L.
   Chimpanzee hand preference in throwing and infant cradling: Implications
   for the origin of human handedness.
   Current Anthropology, 1993 Dec, v34 (n5):786-790.
   ABSTRACT: Responds to W. H. Calvin's (1983) hypothesis that right-handed
   throwing in humans has evolved as a result of a left-hemisphere
   specialization for planned sequential movements, and that it has been more
   predominant in females due to infant carrying on the left arm.
   Observations of throwing were made on 36 chimpanzees to see whether
   nonhuman primates exhibit population level hand preference. 24 Subjects
   were categorized as right-handed, 9 as left-handed, and 3 as ambidextrous.
   Observations of infant cradling were made on 12 captive mother-infant
   pairs of chimpanzees. Seven mothers exhibited a left-side bias and 5
   exhibited a right-side bias; however, infants favored hand preferences
   opposite to their mothers' cradling preferences. These data partially
   support Calvin's hypothesis; handedness may have been influenced by
   evolutionary selection for throwing. However, this effect is neither
   specific to homonid evolution, nor especially pronounced in females.
   Corballis, Michael C.
   Laterality and human evolution.
   Psychological Review, 1989 Jul, v96 (n3):492-505.
   ABSTRACT: The question of whether there is a fundamental discontinuity between
   humans and other primates is discussed in relation to the predominantly
   human pattern of right-handedness and left-cerebral representation of
   language. Both phenomena may go back at least to Homo habilis, 2-3 million
   years ago. However, a distinctively human mode of cognitive representation
   may not have emerged until later, beginning with H. erectus and the
   Acheulean tool culture about 1.5 million years ago and culminating with H.
   sapiens sapiens and rapid, flexible speech in the last 200,000 years. It
   is suggested that this mode is characterized by generativity, with
   multipart representations formed from elementary canonical parts (e.g.,
   phonemes in speech, geons in visual perception). Generativity may be
   uniquely human and associated with the left-cerebral hemisphere. An
   alternative, analogue mode of representation, shared with other species,
   is associated with the right hemisphere in humans.
   MacNeilage, Peter F.; Studdert-Kennedy, Michael G.; Lindblom, Bjorn.
   Primate handedness reconsidered.
   Behavioral & Brain Sciences, 1987 Jun, v10 (n2):247-303.
   Pub type: Literature Review; Review.
   ABSTRACT: Discusses population-level hand use asymmetries in nonhuman primates.
   Studies indicating left-hand preferences for reaching and right-hand
   preferences for manipulation and practiced performance in stereotyped
   situations are reviewed. It is argued that previous negative conclusions
   on preferences were due to methodological problems (e.g., failure to
   emphasize serial trends). Primate handedness patterns are believed to have
   evolved with adaptations to feeding and to be precursors of human
   hemispheric specialization patterns. It is suggested that left-hand
   specialization evolved with the prehensile hand, followed by evolution of
   right-hand specialization with the development of the opposable thumb. 25
   commentaries and a response to those commentaries by the authors are
   MacNeilage, Peter F.
   The "postural origins" theory of primate neurobiological asymmetries.
   IN: Biological and behavioral determinants of language development.; Norman
   A. Krasnegor, Duane M. Rumbaugh, Richard L. Schiefelbusch, Michael
   Studdert-Kennedy, Eds. Lawrence Erlbaum Associates, Inc, Hillsdale, NJ, US.
   1991. p. 165-188.
   ABSTRACT: (from the book) discusses a theory of how cerebral hemispheric
   specialization evolved in primates; argues that asymmetries in cerebral
   function emerged due to an adaptation of posture in the aboreal habitat of
   early primates; postulates that both handedness and communicative capacity
   become dependent on " ...whole-body postural organization"; asserts that
   validity of the theoretical position hinges in part upon the observation
   that "human footedness, a necessarily postural specialization, has a
   stronger contralateral relation to language specialization in humans than
   does handedness; evidence for the theory is reviewed in the context of
   studies that indicate a preference for left-hand-right-hemisphere
   specialization of visually guided reaching and a corresponding
   right-side-left-hemisphere postural control specialization in primates;
   reviews the implications of his theory for the ontogenesis of language.
   Corballis, Michael C.
   The lopsided ape: Evolution of the generative mind. Oxford University
   Press; New York, NY, US, 1991.
   ABSTRACT: (from the jacket) In "The Lopsided Ape," Corballis takes us on a
   fascinating tour of the origins and implications of the specialization of
   the two halves of the brain--known as laterality--in human evolution. He
   begins by surveying current views of evolution, ranging from the molecular
   level--the role of viruses, for instance, in transporting genes between
   species--to the tremendous implications of such physical changes as
   walking on two feet.... Corballis argues that the evolution of the
   brain--and language--was intimately tied up with these changes: The
   proliferation of objects made by early hominids, in an increasingly
   artificial environment marked by social cooperation, demanded greater
   flexibility in communication and even in thinking itself. These
   evolutionary pressures spurred the development of laterality in the brain.
   He goes on to look at the structure of language, following the work of
   Noam Chomsky and others, showing how grammar allows us to create an
   infinite variety of messages. In examining communication between animals
   and attempts to teach apes and dolphins language, he demonstrates that
   only humans have this unlimited ability for expression--an ability that he
   traces back through hominid evolution. After this engrossing account of
   what we know about evolution, language, and the human brain, Corballis
   suggests that the left hemisphere has evolved a Generative Assembling
   Device, a biological mechanism that allows us to manipulate open-ended
   forms of representation and provides the basis for mathematics, reasoning,
   music, art, and play as well as language and manufacture. It is this
   device, he writes, that truly sets us off from the apes.... Both a
   detailed account of human language and evolution and a convincing argument
   for a new view of the brain, "The Lopsided Ape" provides fascinating
   insight into our origins and the nature of human thought itself.
   Are humans unique?
   Human evolution.
   The human condition.
   Human handedness.
   Human language.
   The evolution of language.
   Language and the brain.
   Praxis and the left brain.
   The generative mind.
   The duality of the brain.
   The plastic brain.
   Macneilage, Peter F.
   The evolution of hemispheric specialization for manual function and
   IN: Higher brain functions: Recent explorations of the brain's emergent
   properties. Wiley series in neurobiology.; Steven P. Wise, Ed. John Wiley
   & Sons, New York, NY, US. 1987. p. 285-309.
   ABSTRACT: (from the chapter) reevaluation of the evolution of hemispheric
   specialization for language and its relation to hemispheric specialization
   for manual function... characterization of the nature of language form...
   functional discontinuity between hominids and other primates in language,
   in handedness, and in the left hemispheric specializations related to
   both... ways in which language and manual actions are functionally
   related, which may have important implications.

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