Lest anyone reading this journal of a primitive man should think we spend our time mired in abstractions, let me also say that I am discovering the richness available to those who are willing to alter their major characteristics. The variety of emotions available to a reconfigured human mind, thinking thoughts impossible to its ancestors...
The emotion of -*-, describable only as something between sexual love and the joy of intellection—making love to a thought? Or &&, the true reverse of pain, not "pleasure" but a "warning" of healing, growth and change. Or (^+^), the most complex emotion yet discovered, felt by those who consciously endure the change between mind configurations, and experience the broad spectrum of possibilities inherent in thinking and being.
—Greg Bear, Eon
So... I'm basically on board with that sort of thing as a fine and desirable future. But I think that the difficulty and danger of fiddling with emotions is oft-underestimated. Not necessarily underestimated by Greg Bear, per se; the above journal entry is from a character who was receiving superintelligent help.
But I still remember one time on the Extropians mailing list when someone talked about creating a female yet "otherwise identical" copy of himself. Something about that just fell on my camel's back as the last straw. I'm sorry, but there are some things that are much more complicated to actually do than to rattle off as short English phrases, and "changing sex" has to rank very high on that list. Even if you're omnipotent so far as raw ability goes, it's not like people have a binary attribute reading "M" or "F" that can be flipped as a primitive action.
Changing sex makes a good, vivid example of the sort of difficulties you might run into when messing with emotional architecture, so I'll use it as my archetype:
Let's suppose that we're talking about an M2F transformation. (F2M should be a straightforward transform of this discussion; I do want to be specific rather than talking in vague generalities, but I don't want to parallelize every sentence.) (Oddly enough, every time I can recall hearing someone say "I want to know what it's like to be the opposite sex", the speaker has been male. I don't know if that's a genuine gender difference in wishes, or just a selection effect in which spoken wishes reach my ears.)
Want to spend a week wearing a female body? Even at this very shallow level, we're dealing with drastic remappings of at least some segments of the sensorimotor cortex and cerebellum—the somatic map, the motor map, the motor reflexes, and the motor skills. As a male, you know how to operate a male body, but not a female one. If you're a master martial artist as a male, you won't be a master martial artist as a female (or vice versa, of course) unless you either spend another year practicing, or some AI subtly tweaks your skills to be what they would have been in a female body—think of how odd that experience would be.
Already we're talking about some pretty significant neurological changes. Strong enough to disrupt personal identity, if taken in one shot? That's a difficult question to answer, especially since I don't know what experiment to perform to test any hypotheses. On one hand, billions of neurons in my visual cortex undergo massive changes of activation every time my eyes squeeze shut when I sneeze—the raw number of flipped bits is not the key thing in personal identity. But we are already talking about serious changes of information, on the order of going to sleep, dreaming, forgetting your dreams, and waking up the next morning as though it were the next moment. Not informationally trivial transforms like uploading.
What about sex? (Somehow it's always about sex, at least when it's men asking the question.) Remapping the connections from the remapped somatic areas to the pleasure center will... give you a vagina-shaped penis, more or less. That doesn't make you a woman. You'd still be attracted to girls, and no, that would not make you a lesbian; it would make you a normal, masculine man wearing a female body like a suit of clothing.
What would it take for a man to actually become the female version of themselves?
Well... what does that sentence even mean? I am reminded of someone who replied to the statement "Obama would not have become President if he hadn't been black" by saying "If Obama hadn't been black, he wouldn't have been Obama" i.e. "There is no non-black Obama who could fail to become President". (You know you're in trouble when non-actual possible worlds start having political implications.)
The person you would have been if you'd been born with an X chromosome in place of your Y chromosome (or vice versa) isn't you. If you had a twin female sister, the two of you would not be the same person. There are genes on your Y chromosome that tweaked your brain to some extent, helping to construct your personal identity—alleles with no analogue on the X chromosome. There is no version of you, even genetically, who is the opposite sex.
And if we halt your body, swap out your Y chromosome for your father's X chromosome, and restart your body... well. That doesn't sound too safe, does it? Your neurons are already wired in a male pattern, just as your body already developed in a male pattern. I don't know what happens to your testicles, and I don't know what happens to your brain, either. Maybe your circuits would slowly start to rewire themselves under the influence of the new genetic instructions. At best you'd end up as a half-baked cross between male brain and female brain. At worst you'd go into a permanent epileptic fit and die—we're dealing with circumstances way outside the evolutionary context under which the brain was optimized for robustness. Either way, your brain would not look like your twin sister's brain that had developed as female from the beginning.
So to actually become female...
We're talking about a massive transformation here, billions of neurons and trillions of synapses rearranged. Not just form, but content—just like a male judo expert would need skills repatterned to become a female judo expert, so too, you know how to operate a male brain but not a female brain. You are the equivalent of a judo expert at one, but not the other. You have cognitive reflexes, and consciously learned cognitive skills as well.
If I fell asleep and woke up as a true woman—not in body, but in brain—I don't think I'd call her "me". The change is too sharp, if it happens all at once.
Transform the brain gradually? Hm... now we have to design the intermediate stages, and make sure the intermediate stages make self-consistent sense. Evolution built and optimized a self-consistent male brain and a self-consistent female brain; it didn't design the parts to be stable during an intermediate transition between the two. Maybe you've got to redesign other parts of the brain just to keep working through the transition.
What happens when, as a woman, you think back to your memory of looking at Angelina Jolie photos as a man? How do you empathize with your past self of the opposite sex? Do you flee in horror from the person you were? Are all your life's memories distant and alien things? How can you remember, when your memory is a recorded activation pattern for neural circuits that no longer exist in their old forms? Do we rewrite all your memories, too?
Well... maybe we could retain your old male brainware through the transformation, and set up a dual system of male and female circuits... such that you are currently female, but retain the ability to recall and empathize with your past memories as if they were running on the same male brainware that originally laid them down...
Sounds complicated, doesn't it? It seems that to transform a male brain into someone who can be a real female, we can't just rewrite you as a female brain. That just kills you and replaces you with someone re-imagined as a different person. Instead we have to rewrite you as a more complex brain with a novel, non-ancestral architecture that can cross-operate in realtime between male and female modes, so that a female can process male memories with a remembered context that includes the male brainware that laid them down.
To make you female, and yet still you, we have to step outside the human design space in order to preserve continuity with your male self.
And when your little adventure is over and you go back to being a man—if you still want to, because even if your past self wanted to go back afterward, why should that desire be binding on your present self?—then we've got to keep the dual architecture so you don't throw up every time you remember what you did on your vacation.
Assuming you did have sex as a woman, rather than fending off all comers because because they didn't look like they were interested in a long-term relationship.
But then, you probably would experiment. You'll never have been a little girl, and you won't remember going through high school where any girl who slept with a boy was called a slut by the other girls. You'll remember a very atypical past for a woman—but there's no way to fix that while keeping you the same person.
And all that was just what it takes to ranma around within human-space, from the male pole to the female pole and back again.
What if you wanted to move outside the human space entirely?
In one sense, a sex change is admittedly close to a worst-case scenario: a fixed target not optimized for an easy transition from your present location; involving, not just new brain areas, but massive coordinated changes to brain areas already in place.
It might be a lot easier to just add one more emotion to those already there. Maybe.
In another sense, though, a sex change is close to a best-case scenario: the prototype of your destination is already extensively tested as a coherent mind, and known to function well within a human society that already has a place for it (including companions to talk to).
It might be a lot harder to enter uncharted territory. Maybe.
I'm not saying—of course—that it could never, ever be done. But it's another instance of the great chicken-and-egg dilemma that is the whole story of present-day humanity, the great challenge that intelligent life faces in its flowering: growing up is a grownup-level problem. You could try to build a cleanly-designed artificial grownup (self-improving Friendly AI) to foresee the pathway ahead and chart out a nonfatal course. Or you could plunge ahead yourself, and hope that you grew faster than your problems did.
It's the same core challenge either way: growing up is an adult problem. There are difficult ways out of this trap, but no easy ones; extra-ordinary solutions, but no ordinary ones. People ask me why I take all these difficulties upon myself. It's because all the easier ways, once you examine them in enough fine detail, turn out to be illusions, or contain just as much difficulty themselves—the same sort of hidden difficulty as "I'd like to try being the opposite sex for a week".
It seems to me that there is just an irreducible residue of very hard problems associated with an adult version of humankind ever coming into being.
And emotions would be among the most dangerous targets of meddling. Make the wrong shift, and you won't want to change back.
We can't keep these exact human emotions forever. Anyone want to still want to eat chocolate-chip cookies when the last sun grows cold? I didn't think so.
But if we replace our emotions with random die-rolls, then we'll end up wanting to do what is prime, instead of what's right.
Some emotional changes can be desirable, but random replacement seems likely to be undesirable on average. So there must be criteria that distinguish good emotional changes from bad emotional changes. What are they?
Z M Davis, "Autogynephilia" is a theory, based on the observation that some M-F transsexual people are sexually aroused by female behaviour, which imagines that the arousal causes the desire to appear female. However, in reality the desire may be caused by other circumstances, such as innate brain differences, and supporters of autogynephilia theory have not established the causal link.
It is a failure of the imagination, an attempt to enforce the map on the reality. There are men, and there are women, in the map. Here is a woman with testicles. The map says that cannot be so, the person is a man. However, reality ought to trump the map.
The point of the post still stands. A man does not use a woman's body, and would have to learn how to do so. A man does not use a woman's brain, and would have to learn how to do so. Whether after the change was made it was "the same person" depends on what you mean by "the same person". Upgrading an adult brain is a very difficult problem.