Homosexuality occurs in all human races and has been present since recorded history. It is probable that it has been present since the early millennia of human evolution and in hominid mspecies before man. Homosexuality would have promoted bonding between males of the same family group rather than competition leading to elimination of weaker male members. Rather than hunting as individuals, males worked as a team, greatly enhancing the group's hunting prospects.
Homosexuality would also have facilitated greater separation of the sexes and would have encouraged bands of males to range further afield from an established base, again improving hunting prospects and leading to greater tribal dispersion. The individual with the behavioral anomaly may be doomed to genetic oblivion but the tribal group of which he was a member had improved survival prospects.
It is postulated that a mechanism has evolved in the genes determining instinctive sexual behavior allowing for this anomalous behavior to occur at random but with a determined frequency. This instability of genetic expression is inherited by all humans; the actual variation in genetic expression itself is not. Homosexuality no longer gives survival advantage to our species but there is persistence of this hereditary pattern and continuing occurrence of the behavior variation.
Homosexuality may be defined as sexual relationship between individuals of the same sex, and a homosexual person as one who obtains sexual satisfaction predominantly or exclusively from such a relationship. It is regarded as a variation in sexuality and by biologists as an abnormality for the reason that such a form of sexual activity does not lead to species reproduction. A difference has been found in the hypothalamic structure between heterosexual and homosexual men (1). Prior to this unconfirmed report there were no anatomical, hormonal, or other demonstrable physiological variations in homosexuals when any such measured variables are compared to a matched population whose sexual activity is predominantly or exclusively heterosexual. Psychological or psychoanalytical explanations for homosexual behavior are unconvincing. Evidence of effeminate behavior (2) and stronger maternal affiliation in male homosexuals during childhood may be a result of sexual preferences already established before puberty rather than the cause of such sexual preferences in adult life. Homosexuality is now not regarded as an illness or a psychological disorder although it is accepted that an individual's anxiety about his or her sexual preferences may lead to psychological illness (3).
Prevalence and History
Homosexuality occurs in all races including primitive tribal societies4. Kinsey estimated the incidence of male preferential homosexuality to be between 4% of adult American males (exclusive homosexuality) to 13% (predominantly homosexual) (5). More recent surveys show a much lower incidence with approximately 4% of respondents overall reporting any homosexual experience (6,7). However a majority of sexually active males, deprived of heterosexual contact for a prolonged period will revert to homosexual behavior (8). Apparent variation in the prevalence of homosexuality within different societies may reflect acceptance or tolerance of the practice within a particular society rather than its actual occurrence. It is not a recent abnormality of sexual behavior; references to homosexuality occur in English literature throughout the middle ages and into the nineteenth century and are found in ancient Chinese, Roman and Hebrew manuscripts. References abound in classical Greek writings (4). Reference to homosexual relationship has been found in the earliest cuneiform script on the clay tablets of the Assyrians. Many of the cave paintings or carvings of early man have been interpreted as having a sexual significance; many could equally be interpreted as being homosexual. Some clearly depict homosexual behavior (Figure 1). There is thus evidence of homosexual behavior since our earliest recorded history.
Any deliberate record of our existence spans no more than one hundredth part of the period since we developed as a species. It is postulated that homosexual behavior dates from the time when our species was first evolving and it was probab;y present in hominids (Homo erectus) prior to the appearance of Homo sapiens.
Survival advantages resulting from homosexuality
Early man is thought to have been organized into family groups within tribal areas (9). In these communities the one time "traditional" role of the sexes had evolved, with the males carrying out hunting, foraging and marauding expeditions, moving in packs or bands, while the females remained in proximity to the group's base area or haven, caring for children and maintaining the shelter.
Sexually mature males may seek sexual gratification several times within a week. The frequency of sexual activity may vary according to nutrition, stress, and other environmental factors. However there is no reason to assume that the sexual proclivity of fit early man living on a high protein diet would have been any less than it is today. The human male, apparently unlike some other mammalian species, experiences sexual arousal in the absence of a receptive mate and will actively seek out a sexual partner.
Females would have been restricted in their movement from the home shelter due to repeated pregnancies and the presence of totally dependent infants and perhaps several partially dependent children. The reasons why man, alone among the mammals has children who are totally helpless at birth and remain dependent on parents for years relate to brain size. Despite the anatomical modifications to the female pelvis, stretching of ligaments and fetal skull molding at birth there is still the requirement for brain growth to occur after birth.
Female mobility is restricted by the anatomical structure of the pelvis and the presence of dependent children. This restriction on the movement of females would normally have discouraged males from long absences from the base areas.
The presence of one or more males within an all male group willing to act as the receptive partner in multiple sexual acts would have promoted the readiness of the male hunter group to move away from the base haven for more prolonged periods, greatly increasing the range of these expeditions.
The duration of the absence would have been determined usually by the overall success of the hunt but on some occasions other factors may have been important such as seeking out new hunting areas, finding edible fruits or root vegetables, pursuit of unusual game, locating improved refuges or even exploration for its own interest. Provided the absence of the males from the family group area did not exceed the length of the female menstrual cycle the fertility of the clan would not be greatly impaired, particularly if these cycles were synchronized. If a new, uncrowded or more suitable haven was located by the all male expedition part or whole of the family group, including women and dependent progeny would then move together to the new site.
In other mammalian species males compete for the females to such an extent that only one dominant adult male may remain in the family group, weaker males are eliminated at least until the time when they might challenge for leadership. In human tribal society a pattern of dominance is established but all males remain within the group and cooperate in hunting, foraging and marauding expeditions. Male homosexuality would promote this collaboration and even allow for bonding within the group so that the hunters worked as a team. Bands of males with an acknowledged leader worked in cooperation in the field of the hunt, providing mutual protection and enabling the group to attack or to trap and kill very much larger species, developing techniques that may have resulted in the extinction of several such species.
The family group in which the males had sought out new hunting areas, had collaborated in improving the efficiency of the hunt, had found improved shelter, and where all members enjoyed a greater variety of food would have survival advantages in comparison to a group where the males remained in close proximity to the base and hunted as individuals. Enhanced survival would be due to not only improved nutrition, less crowding and better shelter but also to other environmental effects such as diminished disease prevalence following movement to an uncontaminated living area.
Female homosexuality, at least exclusive homosexuality, is less common than male homosexuality but is probably of equal antiquity (10). The female homosexual may well have acted as a leader among the females during the male absence from the sanctuary area, providing and organizing protection and communal defense as well as substitute sexual satisfaction. Homosexual behavior is common in other mammalian species but the human would appear to be the only species in which exclusive homosexuality occurs. The human species is also the only mammalian species in which the female's mobility may remain greatly restricted by repeated pregnancies and the presence of one or more almost totally dependent offspring throughout most of her adult lifetime.
In summary, both male and female homosexuality in tribal communities early in man's evolution would have facilitated separation of the sexes, enabling the male members of the tribe to work as a team with greater range in their hunting, foraging, marauding, and exploring expeditions while at the same time allowing residual protection for the less mobile females and their children. The overall effect of homosexuality within a tribal group would be increased dispersal and improved survival prospects for that group. This would have been at the expense of greatly diminished genetic survival prospects for those individuals showing the behavioral variation.
Homosexuality is, or perhaps was, a form of eusocial behavior, rare but not unknown in mammalian species. It is seen in a well developed form in the naked mole rats of Kenya (Heterocephalus glaber) where only one female in a colony will reach sexual maturity, producing all the pups which are then reared to maturity by sexually inactive colony members (11). In many other mammalian groups there is some sacrifice by the individual for the welfare of the herd or colony; homosexuality may represent similar behavior in the human.
Postulated genetic mechanism of homosexuality
Sexual behavior may considered as instinctive or intuitive, or at least primarily instinctive with subsequent considerable learning modification. This implies a genetic mechanism for the intuitive behavior; DNA of the species acting through its control over the behavior of the individual cells as they build the nervous system of the embryo and play their part in its functioning in the adult (12). No inheritance pattern of homosexuality is apparent although it is commoner in monozygous twins (13). This is as might be anticipated; a common behavioral variation leading to total failure of reproduction cannot be expected to have resulted from a single or several directly inheritable genetic abnormalities. Kinsey himself wrote (5): "If all persons with any trace of homosexual history, or those who were predominantly homosexual, were eliminated from the population today, there is no reason for believing that the incidence of the homosexual in the next generation would be materially reduced." An alternative explanation is that instability or variation of gene expression is the mechanism of the behavioral variation with the inherent instability being transmitted rather than the variation itself.
Variation of somatic gene expression may occur due to gene segment rearrangement, as in the genes coding for immunoglobulins, by variation in transcription, and by variable RNA "tailoring". Recently a further mechanism has been described, hereditary unstable DNA, as a cause of the fragile X syndrome (14). This disease is characterised by mental retardation, behavioral abnormalities and mild dysmorphism; males are more commonly and more severely affected than females. The condition is clearly X-linked with a single locus of major effect mapping to the long arm of the chromosome. Unusual features of the disease are the existence of phenotypically normal carrier males and the phenomenon of anticipation, with the frequency and severity of the illness increasing with subsequent generations. The fragile X contains a DNA sequence that is unstable both in families and in individuals. This is a trinucleotide repeat (CCG) that is at the fragile site and is either amplified or allows the insertion of other unknown DNA sequences. Normal X chromosomes have some 40 copies of the trinucleotide while carriers of disease may have 70 to 200 copies which allows further amplification. Once the sequence is amplified beyond this number it becomes unstable, with the result that different cells within the same tissue, and possibly different tissues in the same individual have a different genetic constitution. The presence of this variable sequence may lead to variation in rate of transcription or deviation of adjacent gene products from normal resulting in a clinical syndrome of variable severity. Similar instability has been postulated as the cause of the anticipation seen also in dystrophia myotonica and variable penetrance of diseases such as adult polycystic kidney disease (15).
Over one hundred fragile sites, of several different types are known in the human genome. One or more such sites may be in areas concerned with inherited behavior patterns. It is proposed that inherited genetic instability in these areas results in a proportion of all individuals being born who have a variation in neuronal development and neuronal linkage which will later result in their sexual preference being directed towards persons of their own gender.
Homosexuality, as a common instinctive sexual behavioral variation results in significantly diminished genetic survival prospects for the individual. It could only persist as a high incidence behavioral abnormality if it conveyed survival advantage to the group of which the individual was a member. Possible survival advantages are described: greater cooperation between individuals of the one gender within the tribe and greater tribal mobility resulting in wider tribal dispersion.
The homosexual should be seen as an individual, selected at random from within a group of twenty to forty male fetuses, perhaps within a group of twice that number of female fetuses by a variation in behavioral gene expression. The individual's chances of personal genetic survival are greatly reduced by this behavioral variation but the survival of the group of which he and she are members would have been enhanced. He or she is the one allotted by the throw of chromosomal dice to be the selected individual.
Women's mobility is no longer restricted by repeated pregnancies and the constant care of dependent infants. Today woman accompanies man to every portion of the Earth's surface, beneath the surface, and into space. Destruction of other species and of members of our own species may be accomplished by trigger or button pressure; killing of large game no longer requires a team of hunters. As a consequence of these changes, survival prospects of groups with homosexual members are no longer improved and may now even be impaired. However a variation in behavior acquired by the species over a period of several hundreds of thousands of years during our early evolution is unlikely to be lost within a millennium.
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