Homosexuality – a Survival Advantage for Early Man
Introduction
History of Homosexuality
Homosexuality is not a recent phenomenon; it is recorded in the earliest human writings and is depicted in petroglyphs. It is well documented in the Greek and Roman civilizations, in the cuneiform writings of the earlier societies along the Tigris and Euphrates rivers, and in the later history of the middle ages.(1) It is present and is common in all races and cultures, including present day hunter-gather societies.(2) However those with same sex orientation are not spread uniformly through Western society communities; many tend to segregate in enclaves within all major cities and many cities such as San Francisco have large congregations. The annual Gay Festival in Rio de Janeiro attracts some 1,500,000 participants.
Any apparent variation in the prevalence of homosexuality in different cultures and races will relate to the level of acceptance in that society. As the late Vern Bullough wrote: ‘… at various times in history they (homosexuals) have been put in asylums, imprisoned, medicated, psychoanalysed, and ostracized …’.(1) To this list may be added incinerated (burnt at the stake) and subjected to aversion therapy.(3) A society that vilifies homosexuality will seem to have fewer homosexuals although the actual number in that society is unchanged – overt behavior becomes hidden.
Supposed causes of homosexuality are as numerous as attempted treatments. Homosexuals are ‘born that way’, have been enticed into homosexuality by an adult, been turned into homosexuals by the lack of a strong parent, been made homosexual by a dominating parent, been trapped in the gang stage of sexual development, been unable to attract a person of the opposite sex, been oversexed or sexually deficient, been at a lower level of human evolution, been rebels against a bourgeois materialistic society, or been victims of various kinds of traumatic experiences.(1) Communist countries have viewed homosexuality with disfavour and as ‘an aberration produced by capitalism’. A favourite, still in vogue among those with fundamental beliefs of one sort or another, is that the homosexual is ‘possessed by the Devil’.(4)
Early Man, Human Evolution and Human Migration
Early man (Homo sapiens) and the hominids that preceded him (Homo erectus) lived in family groups within larger tribal areas.(5) Within these groups there was division of labor with the adult males hunting as a team and the females caring for children and foraging for food. The males were generally more successful in their acquisition of food, acquiring more calories/hour than the females and passing excess provisions on to the females and their progeny.(6)
Our success as a species was in part by the development of reasoning and by the acquisition of coordination skills necessary for the use of weapons and tools.(7) We also developed forms of communication, allowing individuals to work together in such teams. The continuing development of these skills required progressive increase in the size of the human and pre-human hominid brain.(5)
The larger brain required a larger cranium. The increasing infant head size was accommodated by modifications to the size and shape to the female pelvis, relaxation of the pelvic ligaments at term, and molding of the neonatal head during birth.(8) These adaptions are limited due to the necessity for maintaining the stability of the female pelvis and the possibility of neonatal brain damage if there is excessive molding. The further increases in human brain size occurred through brain growth after birth. An immature brain at birth, however, resulted in infant almost totally dependent on the mother and two and three year old children who still required considerable parental support. Man is unique among the mammalia in having offspring that are totally dependent on the mother for at least a year and who are partially dependent for some years later.
The anatomical changes in the female pelvis and the need to support children restricted the mobility of the female in comparison to that of the human and hominid male; this in turn led to the division of labor and provisioning of females and children by the adult males. Sexual proclivity altered in both sexes to maintain pair bonding and provisioning.
Despite this restriction on mobility, modern man migrated out of Africa and moved into Asia, into India, Europe and south-east Asia. Man reached Australia some 65,000 years ago, probably less than 2000 years after the successful African egression. Later movement occurred across the Bering Strait into North and South America. This ability to spread across the entire globe and to settle in six continents is another major factor in our success as a species.
Value of Homosexuality
Homosexual practice in early hunting parties increased the necessary bonding within the team, making it a more effective unit in hunting, particularly in the killing of larger animals.(9) Like the sacred band of Thebes,(10) the men would hold their ground in the face of the charging beast, mortally wounding it even though sustaining injury themselves. They would also acquit themselves well in the inevitable fighting with neighboring tribes.
The increased sexual proclivity would tend to restrict absence from the unit base area for long periods but a self-sufficient group of males would be freed from this restriction. A hunting, exploring party far from base would find new, more suitable areas to occupy. When such an area was located part or all of the family unit would relocate, moving more slowly as a group; the men carrying their weapons and the women supporting the children, carrying their babies and everything else. The tribe that moved would have advantages over those remaining with new food resources, uncontaminated ground and water and less conflict with neighbors.
Kin Selection and Inclusive Fitness
These concepts provide an explanation for altruistic behavior, how an individual will lessen his own survival or reproductive opportunities for the benefit of the herd or group. One cockatoo (Cacatua galarita) in the Australian bush will keep watch from a tree while the remainder of the flock eat the farmer’s wheat on the ground. He lessens his survival prospect by screeching loudly when the farmer with shotgun approaches. Such behavior may be entirely instinctive, the result of an inherited pattern of reaction. The concept was formalized by the late W. D. Hamilton in the form of a mathematical formula, known as ‘Hamilton’s Rule’, which may be loosely stated that intrinsic behavior will increase in frequency where the benefit to the total number of related recipients exceeds that of the cost (survival or reproductive cost) to the altruistic individual.(11) This action is seen and is explained in the extreme example of the eusocial insects such as bees and ants where reproduction is entirely forgone by one cast in favor of the reproduction by selected members of the colony.(12)
Homosexual behavior in early human societies may be shown to conform to Hamilton’s Rule. If the reproductive fitness of one individual is sacrificed (say from four offspring to nil) and the surviving offspring of 20 related others is increased from four to five from improved hunting return and nutrition, then there is clearly increased inclusive fitness in that individual’s group.
Man is no insect but there may be other examples of inclusive fitness ingrained in our genome. Color vision is encoded by a recessive gene on the X chromosome;(13) defective color vision of the common variety is seen mostly in males. The color defective early hunter may not have seen the approaching saber-toothed tiger (decreased survival fitness) but he would have spotted the camouflaged prey animal in the bushes and led the party back to base in the twilight of their hunting day (increased inclusive fitness).(14) Left-handedness may also have had inclusive survival fitness, with the left-handed hunter on the left flank of the animal cordon, club in his left hand.
Inheritance of Homosexuality
A behavioral variation that may reduce reproductive fitness to zero is unlikely to be directly inherited. What is inherited, and inherited by all of us, is the random prospect that we will have same sex orientation.
Same sex orientation is more common in brothers of male homosexuals than in the general population, indicating that selection is not truly random but that genetic or epigenetic factors are involved in a switching process. Studies have shown that when one twin is homosexual, same sex orientation is then more common in monozygous twins (52%) than in dizygotic twins (22%) and in non-twin siblings (11%),(15) compared to a self-reported incidence of 2.8% in the general population.(16)
Division of a single zygote to form monozygotic twins may occur any time from the first day of fertilization up to ten days, rarely even later. Cleavage of the zygote after 8 days results in monoamniotic twins, later cleavage may result in conjoined twins.(17) If the incidence of same sex orientation in monozygotic is compared to that in dizygotic twins the determination of sexual orientation may be estimated to happen five to six days after fertilization. At this time some 50% of the zygotes destined to become twin pregnancies have undergone cleavage.(18) The zygote is in the early blastocyst formation stage and the embryonic cells are commencing specification.(19) Cleavage before five days would result in embryos free to undergo their individual sexual orientation subject to differing epigenetic influences; division after six days results in embryos with concordant orientation. (Other characteristics, such as left or right-handedness, would also be determined at this same stage of development.)
Conclusion
Homosexuality has been present in humans long before there was ever a deliberate record of our existence. Same sex orientation deceases the survival fitness of the individual but at an earlier time in our evolutionary history increased the inclusive fitness of the family group or tribe of which that individual was a member. Homosexuality is still of inclusive benefit to civilized man but in ways that are very different from when it evolved in tribal societies at least two hundred millennia ago.
1. Bullough VL. Homosexuality: A History. New York: NAL; 1979.
2. Schneebaum T. Keep the River on Your Right. New York: Grove Press; 1969.
3. Bancroft J. Aversion therapy of homosexuality. A pilot study of 10 cases. Br J Psychiatry. 1969 Dec;115(529):1417-31.
4. Dimond P. FAQ- Does God Create Homosexuals? http://wwwmostholyfamilymonasterycom/does_God_create_homosexualshtml (accessed 7 September 2010) [serial on the Internet]. 2010.
5. Leakey R. The Origin of Humankind. London: Wedienfeld & Nicolson; 1994.
6. Hill K. Hunting and Human Evolution. Journal of Human Evolution. 1982;11:521-4.
7. Darwin C. The Descent of Man and Selection in Relation to Sex. London: John Murray; 1870.
8. Russell JG. Moulding of the pelvic outlet. J Obstet Gynaecol Br Commonw. 1969 Sep;76(9):817-20.
9. Mackey WC. A cross-cultural analysis of recruitment into all male groups: An ethological perspective. Journal of Human Evolution. 1981;10(3):281-92.
10. DeVoto JG. The Thebian Sacred Band. The Ancient World. 1992;23(2).
11. Hamilton WD. The Evolution of Altruistic Behaviour. The American Naturalist. 1963;97(896):354-6.
12. Attenborough D. Life on Earth: A Natural History. London: Little, Brown & Co; 1981.
13. Jackson CE, Symon WE, Mann JD. X Chromosome Mapping of Genes for Red-Green Colorblindness and Xg. Am J Hum Genet. 1964 Dec;16:403-9.
14. Morgan MJ, Adam A, Mollon JD. Dichromats detect colour-camouflaged objects that are not detected by trichromats. Proc Biol Sci. 1992 Jun 22;248(1323):291-5.
15. Bailey JM, Pillard RC. A genetic study of male sexual orientation. Arch Gen Psychiatry. 1991 Dec;48(12):1089-96.
16. Kendler KS, Thornton LM, Gilman SE, Kessler RC. Sexual orientation in a U.S. national sample of twin and nontwin sibling pairs. Am J Psychiatry. 2000 Nov;157(11):1843-6.
17. Dickinson JE. Monoamniotic twin pregnancy: a review of contemporary practice. Aust N Z J Obstet Gynaecol. 2005 Dec;45(6):474-8.
18. Hall JG. Twinning. Lancet. 2003 Aug 30;362(9385):735-43.
19. Suwinska A, Czolowska R, Ozdzenski W, Tarkowski AK. Blastomeres of the mouse embryo lose totipotency after the fifth cleavage division: expression of Cdx2 and Oct4 and developmental potential of inner and outer blastomeres of 16- and 32-cell embryos. Dev Biol. 2008 Oct 1;322(1):133-44.
A very nice just-so story but a rather unconvincing all the same.
Part of the problem reside in relying on the fraternal birth order effect which, even if it were true – and that doubtful – would account for only one seveth of the prevalence of male homosexuality as defined in terms of men who consider themselves to be exlcusively gay.
If we go right back to Kinsey, although he undoubtedly overestimated the prevalence of exclusive homosexuality, probably by about 3-4 times – his estinates for non-exclusive homosexuality, i.e. men who had experienced some sort of homosexual attraction, even if they hadn’t acted on it, was around four time higher than his estimate for exclusive homosexuality. If we assume that Kinsey was somewhere near the mark on proportions, even if he was out of line on his actual prevalence estimates, then our 1 in 7 for FBOE drops to 1 in 28 and you have 97% of the male population who’ve experience some degree of same sex attraction still to be accounted for.
As FBOE relates to exclusive homosexuality and postulates that the probability of a sibling being gay increases with birth order, you also have the problem – when suggesting that this might have some sort of surivival advantage – of accounting for childhood mortality. Putting all your eggs into the basket of the elder siblings only makes sense if you can be reasonably certain that these will survive long enough to mate and reproduce and I’m really not sure we’re licensed to make that assumption.
I think that in seeking to account for homosexuality alone you’re rather asking the wrong question at the outset.
Homosexuality is seen as significant for primarily social and cultural reasons but if we set those aside for moment and think only in terms of the underlying mechanism of sexual attraction then there is no obvious reason why we should consider same sex attraction to differ from an individual preference for blondes or brunettes or any of the other physical characteristics that provoke an attraction response.
I suspect that a more fruitful line of enquiry may lie in going to back to the notion of imprinting, for which we have some indirect evidence in the Westermarck effect.
I need to blog this properly but I suspect that sexual attraction is a heuristic mechanism which is part biological, i.e. we have an evolved ‘module’ which does the sifting and acts as the trigger for our physiological and emotional responses, but which is ‘content neutral’ at birth such that the mechanism is unconsciously parameterised in the early years of life via environmental stimuli through a process of over which we have no conscious control.
Sexual attraction – an, by extension, homosexuality – is not innate in the purely deterministic sense of our being born with a pre-programmed mechanism which determines precisely who and what we find attractive, but it is de facto innate because the mechanism operates unconciously and we have no concious control over which parameters the mechanism acquires from our surrounding environment. Homosexuality is not, therefore, a direct adaptation by rather a byproduct of an adaptation – sexual attrraction – one of many different outputs that this heuristic mechanism is capable of generating.
This accounts for ubiquity of homosexuality across the entire species and for the fact that it arises even in hostile cultural environment with strong social taboos against same sex attraction. THe observed prevalence of homesexuality is, therefore, merely an expression of the probabilty that this heuristic mechanism will acquire parameters for an attraction to members of the same sex and hence the difficulty that reasearchers are having in finding commonalities that would support either a purely biological or environmental etiology.
I was enticed into heterosexuality by Julie Newmar.
A few points:
This is about homosexuality in men only. Does homosexuality in women not need an explanation?
AFAIK, most current studies suggest that most calories in hunter-gatherer societies come from gathering, not hunting. Hunting is primarily a form a status competition between males. Thing may have been different among our distant ancestors, but then again….
Hamiltons rule would suggest a conditional strategy – if you can ensure the survival of more copies of your genes by forgoing personal reproduction in favour of aiding others raise their offspring, then do so. This calculation would depend on the number of siblings you have, and the number of offspring they have, etc. FBOE suggests that this calculation is done before your siblings are sexually mature. It occurs to me that this could be achieved far more effectively if males were bisexual, and their preference in partner was adjusted in response to the number of successfully reproducing siblings they had. This would seem to allow ones reproductive strategy to be more closely tied to the actual conditions that prevailed when sexually mature, (ie. sexual relationships with both sexes, with a preference for one or the other developing in response to environmental cues).
Further, the group bonding hypothesis, (allowing groups to hunt/fight more efficiently, would also be more efficient if all males were bisexual, allowing them to all to form bonds together while on a hunt. The presence of a small percentage of homosexuals in a group of heterosexuals does not necessarily achieve the same effect. A colour blind person may be able to lead the entire group home through twilight conditions; but it is difficult to see how the bond between two homosexual hunters could aid the survival of other members of the group.
If these are the selection pressures that were at play, then it occurs to me that bisexual men would have had the reproductive advantage. This would appear to result in a pressure towards all men being bisexual, to a degree. But this is not what we find. AFAIK
[…] Homosexuality – a Survival Advantage for Early Man – Butterflies and Wheels John Hayman is a retired pathologist with experience in the diagnosis of diseases associated with HIV infection. He has looked for a reason as to why same sex sexual orientation, with greatly diminished genetic survival prospects for the one individual, should be present with such high frequency in all human populations. ‘Kin selection’ offers an explanation; survival prospects as a whole are enhanced in those family groups having one or more members with same sex orientation. […]
This article is only addressing male homosexuality: why has lesbianism been erased, yet again? I also find it reductionistic: removing free will from the equation, and implying that ‘survival advantage’ is the best explanation for the way people are.
Reading this article, one gets the impression women are dullards who do not need to hone their skills or bond with one another, among other wrong ideas.
Komal, regarding the marginalisation of women, it seems to me that Liam’s first two paragraphs have already asked the crucial questions.
Regarding “reductionistic”: science is reductionist, of necessity, but why is that a bad thing?
Next, where does “free will” fit in?
(1) there’s more than one way of understanding what “free will” means, and
(2) whatever it means, why is it relevant to the question of adaptation or environmental and social viability, and how is it relevant to homosexuality in particular?
Female homosexuality would have had a similar advantage to that of male same sex orientation – facilitating separation of the sexes for extended periods. With the hunter – warriors of the family group over the hills and far away the female, like Joan of Ark, would take responsibility for the defence of the home area, warding off animal predators and with enthusiasm keeping at bay any stray males from a neighbouring tribe. No dullards there.
Just curious:
What about pedophilia?
Not a choice. Who would choose to belong to a group more hated than atheists?
Widespread throughout humanity.
Seems to work against reproductive success.
I have no explanation for pedophilia. If you define normal sex as sexual activity between two freely consenting adults then pedophilia is not normal. I agree that it is widespread throughout humanity and it would seem to work against reproductive success and like homosexuality it has a long recorded history. All I can say is that there is no apparent genetic inheritance pattern and that it is no more common in homosexuals than in heterosexuals. The prevalence of pedophilia weakens my argument that homosexuality was once of kin survival benefit.
Sorry. I didn’t mean to do that. I thought you might be on the track of an Attraction Theory of Everything.
[…] Inclusive fitness and kin selection in an account of homosexuality’s survival value […]
There’s a psychotherapist in America called Salter who works with pedophiles, and she said that the literature is forming a consensus around there being two types of pedophiles. One appears congenital; attracted to prebuscents from an early age, as they age, the age of those they are attracted to do not. She said they are usually attracted to prebuscent boys, are overwhelmingly male offenders, and have very high numbers of victims. Many people who abuse children are not pedophiles, she believes, but sadists.
She also says that there is another category of ‘conditional’ pedophile; a normally heterosexual person who abuses a child under conditions of extreme stress – no-one can posit a reason why they react this way to stress.
With regard to homosexuality, my wife came up with another hypothesis. With regard to male coalitions, a male homosexual could be a valuable asset, in that they can be a valuable partner, but not someone competing for the attention of women. They also may allow heterosexual males to leave camp for an extended period of time, while leaving a protective male behind without the fear of cuckoldry. This makes even more sense if the coalition is made up of older brothers with whom one shares DNA.
I think that there may have been several different scenarios but the overall conclusion is that homosexuality, both male and female, was of kin survival benefit. I cannot see how pedophilia could have been of such benefit.
Hi there,
I’m sure you’re aware of the work done by Muscarella on the evolutionary advantages of human same-sex attraction – basically his position is more or less the same as yours. It is also similar to the kin selection hypothesis outlined by E. O. Wilson back in 1975, in which homosexual behaviour is posited as a mechanism designed (by natural selection of course) to make some individuals help their siblings raise their young, forfeiting their own reproduction. In your theory, you suggest that homosexual behavior arose as a mechanism for social bonding amongst hunter-gatherer societies, so that individuals so bonded would gain a fitness advantage over individuals less able to establish such cooperative bonding.
Problem is, as in the case of Wilson’s hypothesis, there is quite a difference between showing the evolutionary advantages of cooperation (which has indeed been demonstrated in quite a lot of research) and showing that homosexual behaviour is a mechanism for obtaining such cooperation. Anthropological data on homosexual behaviour in hunter-gatherer societies does not seem to suggest that hunting parties are bonded by homosexual attraction, or that homosexuality in any way enhances coalitions and alliances.
Moreover, research done on homosexual mating preferences nowadays does not seem to fit the theory. If homosexual behaviour is a mechanism for establishing stable alliances, one should expect to find that homosexual men would find high status men as desiderable (more or less like heterosexual women tend to do). In fact, data shows that by and large homosexual men couldn’t care less about their prospective partner’s status. And they are not overly concerned with long-lasting partnerships (“alliances”) until they are in their 30s or later. Indirect data, to be sure, but still something to consider.
So yes, homosexual behavior is still a puzzle from an adaptationist point of view. I think homosexual behavior is more like an evolutionary by-product of human sexual evolution – something that doesn’t have an evolutionary advantage per se, but is linked to something that is, like in Camperio-Ciani’s hypothesis of genes for homosexuality in men linked to evolutionary advantages in heterosexual sisters. But we still don’t know much about the issue.
Some interesting papers on the topic:
Camperio-Ciani, A., Corna, F., & Capiluppi, C. (2004). Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity Proceedings of the Royal Society B: Biological Sciences, 271(1554), 2217.
Kirkpatrick, R., Blackwood, E., Dickemann, J., Jones, D., Muscarella, F., Vasey, P., Williams, W., et al. (2000). The Evolution of Human Homosexual Behavior. Current Anthropology, 41(3), 385–413.
Muscarella, Frank. (2007). The Evolution of Male-Male Sexual Behavior in Humans. Journal of Psychology & Human Sexuality, 18(4), 275–311.
Muscarella, F, Fink, B., Grammer, K., & Kirk-Smith, M. (2001). Homosexual orientation in males: Evolutionary and ethological aspects. Neiroendocrinology Letters, 22(6), 393–400.
[…] have been plenty of occasions where groups of men were out hunting for days or weeks at a time. How were they supposed to deal with testosterone-influenced aggression and the biological goal of se… Perhaps the same way as is common in prisons, among men who would much prefer heterosex, but which […]
It seems to me that homosexual men in early hunting/gathering groups would have been tremendously advantagous. Though not a threat to hetersexual males concerned with mate gaurding the homosexual male possessed the strength and aggression of any other male. They could have a close knit nurturing role-which its been shown modern homosexuals tend toward- while possibly not hunting so much as guarding and being allowed to be available to offspring and females as muscle increasing every member’s chances of still being there and alive when hunters returned. This could explain the continuance of a recessive or fixed ratio of expression type gene. Slightly similar to what’s seen in ants. Division of labor by inborn traits. Obviously, less extensively than in ants where the members of different casts look like different species. In human groups, this occurance helped the species as a whole. Apparently, whatever the advantage was it won out over any groups not containing the genes neccessary for homosexual men to emerge. This happened so long ago that it is uniform and universal in all early cultures. That is to say: its basic and not separable from mankind as a species.
Data showing that the first degree relatives of homosexual men tend toward better success in reproducing by way of increased mating opportunities is very compelling though. If these data are reproduced and its confirmed that those genetically related to homosexuals have more numerous sexual partners and that that is due to their own attractiveness as opposed to their singlemindedness, that would be a much more compelling answer to homosexuality’s evolutionary advantages. This would be more important in the male though. One could assume that in such primitive times females of age were basically almost always pregnant. The race then is determined by which males got there first and often between pregnancies.
I’ve always been under the impresion that aversion to homosexuality was more of a social taboo then an instinctual one. This article seems to assume that a homosextual would neccasaraly have to be present before any other heterosextual male in the tribe would cosider experimenting with another male. Were talking about a hunter/gather society here, people who grew up together like an extended family.
The question I have is wether or not being homosextual in a primative tribe reduces the chance for the homosextual to procreate? Just because they prefered to mate within their gender doesn’t mean they did not want children. Evolution does not care wether a trait is benifical or nutral or even self destructive as long as that trait does not prevent procreation.