(For a fuller treatment of this subject see Chapter Eight, My Genes Made Me Do it!)
For most of the 20th Century brain researchers believed that the brain was a rigidly organised organ with fixed structures: each part having a distinct function that changed very little over time, except to atrophy. But there is clear evidence now that the brain is plastic: living and responsive tissue, subject to considerable change at the micro-level in response to the things we do, imagine and think repeatedly.
Sex and gender researchers believing that the brain and its functions were more or less set, thought they might find evidence in the brain that homosexuality was hard-wired. They looked for signs that parts of the brain used in sexual activity were different in homosexuals and heterosexuals, that, for example, a homosexual male brain might be more like a female brain.
Almost without exception these numerous studies produced contradictory conclusions, and were not replicable. Although gay activism sought to use some of these findings to argue homosexuality is biologically ingrained, the most that can be said scientifically about them is that IF any differences exist they are probably the result of homosexual behaviour rather than the cause of it.
It is clear now that no-one is stuck with the type of brain they were born with. Our assumption now should be, change is possible in many behaviours – sexual orientation not excluded - and extraordinary effort will produce extraordinary change.
During the decades in which scientists used to think structures in the brain governed most behaviour, the onus was on objectors (whom we could call developmentalists) to show otherwise. The discoveries of the last decade or two reverse this. Behaviours (even reflexes) are so changeable with training that the onus is now on essentialists to prove that some particular behaviour is permanently governed by brain structure. Brain structure itself is definitely changed by experience and training. Essentialists must now show that not only are there brain differences, but that these were present at birth, are not the result of training or experience, and inevitably produce their results later in life. Apart from the grave logistic difficulties in the experiments we doubt this research will ever succeed. There is too much evidence the other way.
The young brain
It is fair to say that the brain, but particularly the immature brain, is like a computer which is constantly reprogramming itself, but including genuinely random actions as well. Particularly in children, neurons fire at random, and if that neural path is reinforced through experiences the path becomes fairly permanent, though not set in concrete. If it is not reinforced, the path becomes hard to excite, and eventually its neurons get pruned. Extensive stimulation is needed or pathways do not develop, and some periods are more important for certain kinds of stimulation than others. For example, if a child is deprived of light to the eyes in a critical early period, it develops childhood cataracts and becomes blind. If an adult is deprived of light for a few weeks, no such damage happens. 4
Similarly if a child does not hear the different “l” and “r” sounds in adult speech (for example in Japan) they will find it hard as an adult to hear any difference, let alone pronounce them, but even so, enough concentrated practice will slowly achieve this.
The maturation of the brain happens in many cycles of neuronal growth and pruning. The last of these cycles is in the early twenties, and cycles can vary from a few months to several years. 24 For each growth cycle, experiences reinforce some of the neuronal pathways and the rest get pruned. One consequence of this is the important lesson, Don’t take too much notice of assertions about sexual orientation in adolescence. Change is still happening. For any adolescent reading this – don’t prematurely label yourself, you may well change!
Changes in the adult brain
But changes take place in the adult brain too, particularly with training and these changes can be picked up in brain scans within minutes as blood flows begin to move towards the area being exercised. Monkey experiments have shown that artificial exercise of three digits on the hand increases the area of the brain associated with those fingers and decreases the other regions proportionately (4). Violinists have a grossly enlarged area of the brain devoted to the fingers of their left hands. Those who learn a juggling routine for three months produce observable small changes in the small-scale structure of the brain, and these changes reverse when they stop. 20
London taxi drivers have an enlarged area of the brain dealing with navigation. Is this innate? No. London bus drivers on set routes did not have this enlarged area, and on retirement of the taxi drivers, the brain area involved diminished.25 Taxi-drivers were not born that way, but developed the brain area through huge amounts of navigation and learning, and only maintained it through constant use.
We change our brains at the micro-level through the way we exercise, and anything we do repetitively especially if associated with pleasure (e.g.) sexual activity. So, if brain scientists did find real differences between the brains of homosexuals and heterosexuals, this was probably the result of different sexual behaviours, not the cause of them.
There is nothing permanent either about changes to brain microstructure as a result of learning and activity. Measurements of (radioactive) carbon-14 in human brains show that the average carbon atom stays about seven years in brain tissues. This means that the complete material of the brain is changed during a lifetime by substitutions of different atoms and brain cells - even in "permanent" nerve tissue.10 Nothing is hardwired beyond possibility of change. Anyone determined to change any behavior should be able to make a substantial difference in thinking and habit patterns within a decade, but usually much sooner.
The evidence is that post-natal training and experience are mostly responsible for the microstructure of brains. We predict that some research may eventually show real and replicable differences, between homosexual and heterosexual brains, but this is primarily the result of consistent and intense behaviour - training, if you like.
Neurons that Fire together Wire together
We strongly recommend the book by Doidge: The Brain that Changes Itself (23). This remarkable but very accessible work describes the overthrow of 20th century beliefs about the unchanging nature of the brain. The brain can change a huge amount, very encouraging news to anyone who is stuck in any habit or pattern of behaviour.
Doidge gives a neurological principle: Neurons which fire together wire together. In human sexuality this means that if something extraneous is often associated with sexual arousal it will tend to become part of it. So, it becomes very reasonable to suppose that (for example) intense emotional focus on someone of the same sex might get triggered together with sexual excitement, and if frequently repeated can ultimately seem to be very deeply ingrained homosexuality.
Because of brain plasticity it’s quite possible that homosexuals can become more heterosexual and heterosexuals more homosexual, though persistent work could be needed, about equivalent to mastering a new musical instrument.
Don’t use it and you’ll lose it
Doidge shows that various skills and behaviours are indeed organised in distinct brain regions but that the micro-details (or “brain-map”) are dynamic and changing on a day- to day basis. If one part of the brain is suddenly not used, the areas around it immediately start to recruit these unused brain cells for other purposes, re-program them and use them. Eg parts of the brain involved in the functioning of a lost limb can be repurposed, parts of the brain used in a now-discarded skill can be recruited for another very different skill. Doidge sums up the extraordinary plasticity of the brain with the words, Use it or lose it. (Or, for those trying to drop an unwanted behaviour, Don’t use it, and you’ll lose it. )
Even if part of the brain is strongly associated with a particular sexuality it should be possible to change it. Stopping a sexual activity and avoiding stimulation of that brain region, and plunging into some other intense brain activity for months would lead to a diminishing of the intensity of that sexual response. Months is about the timescale of first significant change. That can be true in learning a musical instrument too!
Doidge’s conclusion about sexuality is that "Human libido is not a hardwired invariable biological urge, but can be curiously fickle, easily altered by our psychology and the history of our sexual encounters." and “It's a use-it-or-lose-it brain, even where sexual desire and love are concerned.” This would apply both to same-sex attraction and opposite-sex attraction.
If we train hard enough, an activity can become automatic and we pay it less conscious attention. That is particularly true of playing a musical instrument. Many of the basic techniques like chords, scales and arpeggios, are so deeply learnt that we don’t think about the details and indeed can’t if the music is fast. Details of driving, throwing a ball, reading, even tying shoe-laces don’t and often can’t demand full attention. Anything we do often, we often end up doing automatically. In the same way it can seem that sexual orientation is so deeply embedded that it is innate. But, really, it is no more innate than any complex skill we have worked at for years to the point where we can do it on auto-pilot, without thinking.
Scientists have not been able to find clear gender-related structural differences between the brains of boys and girls at birth. At that stage of life their properties and functions overlap almost entirely. The same is true for behaviors. Male and female behavior - let alone homosexuality and heterosexuality - is apparently not hardwired into the brain at birth. In fact, only one quarter of the brain is formed in a new-born child; the rest is developed through learning and experience (environmental input). We can be confident that whatever male/female differences exist in adult brains (and, no doubt, more will be found at some stage), they will be largely shaped by learning and behavior. But what learning and experiences do to the brain is not set in concrete either. Brain cells are replaced in roughly seven year cycles, meaning that new neuron pathways can be formed and old ones reshaped. Intensive exercise, training or imagination changes the brain microstructure. We are not victims of our biology or the experiences which shape the detail of our brain. Anatomy is not destiny; change is always possible. The brain is plastic and is in a constant state of change. Indeed the question is rather: what change is not possible?
We would not want to say that the structure of the brain you were born with has no effect. It has. It can be profound. But that structure can also be profoundly changed, and we don’t yet know the limits. They are probably sky-high.
4. Kandel, E.R., Hawkins, R.D., The biological basis of learning and individuality, Scientific American (March 1992) 267:53-60
10. Stenhouse, M.J., Baxter, M.S., Bomb 14C as a biological tracer, Nature (1977) 267:828-832.
20. Draganski, B. Gaser, C., Busch, V., Schuierer, G., Bogadahn, U., May, A. (2004) Neuroplasticity: changes in grey matter induced by training. Nature 427, 311-312.
23. Doidge, N. (2007) The Brain that Changes Itself: Penguin, New York.
24. Barry, R.J., Clarke, A.R., McCarthy, R., Selikowitz, M., Johnstone, S.J. and Rushby, J.A. (2004) Age and gender effects in EEG coherence: I. Developmental trends in normal children. Clinical Neurophysiology 115, 2252-2258.
25. Maguire, E.A., Woollett, K. and Spiers, H.J. (2006) London taxi drivers and bus drivers: a structural MRI and neuropsychological analysis. Hippocampus 16, 1091-1101.
See also Chapter Eight, My Genes Made Me Do It!