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But first, let us outline a very different, bioconservative vision, perhaps best represented today by the distinguished geneticist at University College London, Professor Steve Jones.

Two Contrasting Views of Future Human Evolution

Genetic Roulette versus Designer Babies

This conjecture isn't premature. For example, people who inherit two copies of a "short" version of the chromosome 17 serotonin transporter gene, 5-HTTLPR, have an 80 per cent chance of becoming clinically depressed if they experience three or more negative life-events in five years. By contrast, genetically resilient people who inherit the long version have only a 30 per cent chance of developing mental illness in similar circumstances. If offered the choice via preimplantation diagnosis (PGD), would you opt for the short or the long serotonin transporter gene variant for your future child? Or would you decline to choose, putting your faith in God or Mother Nature?

Right now, of course, this kind of scenario still sounds far-fetched. Later this century and beyond, are prospective parents really going to enroll for courses in behavioural genetics and molecular biopsychiatry before having kids? For sure, certain genetic decisions are in principle straightforward, for example gender selection, or whether to pass on a cystic fibrosis allele. Such decisions are taken by some prospective parents in a few countries already. But other genetic decisions will be much more complicated, not least for "mood genes" that help determine a person's average level of well-being or ill-being over a lifetime.

For what it's worth, I personally think that taking advanced courses in behavioural genetics, or at least seeking genetic counselling, will be morally incumbent on anyone before s/he assumes the immense responsibility of having a child. Yet this kind of education is unlikely to be widespread for the foreseeable future. The argument presented here doesn't depend on it. Instead, in an era of mature reproductive medicine, we may forecast an abundance of user-friendly software tools to enable prospective parents to take responsible genetic decisions - as distinct from blindly taking their chances in the genetic lottery of Darwinian life. For the exponential growth in computing power can be harnessed to a new growth industry of sophisticated baby-authoring software. So the average parent will no more be required to understand molecular genetics than the average contemporary Windows PC user is required to understand machine code. And the parallel goes further. If it's ethically acceptable to spend hours redesigning your Windows PC desktop the way you like it, then why not at least take a few hours to make sure that your future child is psychologically and physically healthy too?

Of course, such authoring tools open up an ethical and regulatory minefield of gargantuan proportions. Yet so does sexual reproduction: playing the genetic equivalent of Russian roulette with a child's life.

Recalibrating the Hedonic Treadmill.
OK, maybe prospective parents will choose to avoid alleles and allelic combinations associated with depression or anxiety disorders or schizophrenia when they prepare to have children. But what grounds are there for thinking that the average hedonic set-point of humankind as a whole will be ratcheted ever upwards? Recall that we all have a kind of inbuilt hedonic treadmill that prevents most of us from remaining extremely happy or extremely miserable for very long - though of course extreme misery can seem like an eternity while it lasts. Our hedonic treadmill tends to have an approximate hedonic set-point around which we fluctuate over time. This hedonic set-point crudely determines the average level of subjective well-being or ill-being that most people experience throughout a lifetime. Of course we're all buffeted by external events, both pleasant and unpleasant, that affect us acutely for good or ill; but over time, we mostly revert to a [partly] heritable individual mean. In some people, the hedonic set-point tends to be fixed below the Darwinian average: such people have a gloomy temperament - what the ancients would have called an excess of black bile. In other people, the hedonic set-point is fixed above average: they are temperamentally optimistic. Some people's mood oscillates sharply, other people are more equable. But the current range of hedonic diversity aside, why may we predict that the typical default state of well-being of the human population is going to increase indefinitely - even after genes predisposing to anxiety disorders and clinical depression have been weeded out of the gene-pool?

The plain answer is that we can't know for sure. So this is speculation. Yet here is a thought-experiment. Imagine that you have the option of choosing the genetic dial-settings of the hedonic set-point of your future child: the degree to which he or she is temperamentally depressive or happy - or superhappy. To keep things simple, I won't yet consider the richer forms of emotional well-being, just normal hedonic tone, which we know is partly heritable. What average level of hedonic tone would you choose for your future child on a 10-point scale? [Here again I am being deliberately simplistic.] On the unscientific basis of a few straw polls conducted over the years, I'd estimate that most people if pressed would opt for a hedonic 8 or 9. Yet a surprising number of respondents say "10": they would like their children to be as temperamentally happy as possible.

Realistically, perhaps only a minority of prospective parents will initially want to have children disposed to be naturally superhappy by contemporary norms. But most parents will want happy children, as distinct from depressive, moody, anxiety-ridden children. Not least, happy children are more fun to raise. Happy, resilient, self-confident children are also more likely to be "successful" over-achievers in the traditional Darwinian sense: we needn't suppose that prospective parents care only about the happiness of their future kids: many parents-to-be are of course highly ambitious for their offspring. Anyhow, on this argument, the average, genetically constrained set-point of emotional well-being of our species is destined to rise over time as a reflection of these individual parental choices, as tomorrow's enhancement technologies shift social norms of well-being and become the next generation's remedial therapies. The depressive realism of one century may become the affective psychosis of the next. Over time, an analogous selection pressure may be exerted in favour of alleles and allelic combinations predisposing to high intelligence - and perhaps even genius and supergenius - although here any contribution to enhanced quality of life will be indirect. In any event, over a whole spectrum of physical and psychological traits, we may predict that germline enhancement will become germline remediation as the average level of biological well-being improves across human society. As biophysicist Gregory Stock notes in Redesigning Humans (2002), "The arrival of safe, reliable germline technology will [...] transform the evolutionary process by drawing reproduction into a highly selective social process that is far more rapid and effective at spreading successful genes than traditional sexual competition and mate selection." Thus the tempo of world-wide mood-enrichment may accelerate.

Critically, the genetic mood-enrichment conjecture doesn't hypothesise the future existence of any mega-project to make a happier world. The possibility of such a pan-global project can't be excluded - grandiose and fanciful as the idea of some kind of Hedonistic Imperative (1995) now sounds. Currently only the tiny Himalayan kingdom of Bhutan officially exalts Gross National Happiness (GNH) over Gross National Product (GNP). If hedonic enrichment were internationalized and pursued with scientific rigour, then the selection pressure against nastier Darwinian genotypes would be even more severe than anticipated here. Now personally, I advocate a world-wide Abolitionist Project laid down as official United Nations policy. Not least, only a global mega-project can ever extend the abolition of suffering to the rest of the living world. Ecosystem redesign, cross-species depot-contraception, and eventually rewriting the whole vertebrate genome can't be achieved via private initiative. However, such a mega-project isn't imminent. Less extravagantly, global mood-enrichment may be the collective outcome of billions of personal reproductive decisions made by individual parents-to-be during the next century and beyond.

Phrased in the language of designer babies, the prospect of species-wide hedonic enrichment evokes sinister images - even though it promises to make the world a much happier place. Do we really want parents controlling the destiny of their future children? But we have to be careful about how we frame the issue here. Just as physical good health is empowering, and doesn't determine what you do with your life, likewise being temperamentally happy and psychologically robust doesn't determine what you actually do with your life either. Like physical health, mental health tends to empower rather than constrain. Genetically hardwired mental superhealth is potentially even more empowering. It makes you psychologically indestructible. It stops you ever becoming depressed or anxiety-ridden - and suffering the crippling loss of life-opportunities that such conditions entail. Moreover, in the future anybody who isn't satisfied with aspects of their core personality, and who doesn't want to use consciousness-altering drugs to change it, can practise somatic gene therapy. We won't always be at the mercy of a scrambled mix of our parent's genes as now, whether those genes have been passed on by accident or design.

Future Nociception: The End of Physical Pain?

Well, there is a short-to-medium term answer and a longer-term answer. Let's consider the short-to-medium term options first.

The Cyborg Solution versus Radical Recalibration.
At present there are different "natural" genetic variants that promote varying degrees of pain-sensitivity e.g. variant alleles of the gene SCN9A coding for the a-subunit of the voltage-gated sodium channel Nav1.7 in nociceptive neurons; the mu opioid receptor gene; and the gene encoding catecholamine-O-methyltransferase (COMT). Few prospective parents in the future are going to want kids who are hypersensitive to physical pain. Most parents, if given the choice, will presumably seek no more than mild-to-modest pain-sensitivity for their offspring. Thus if genetically planned parenthood ever becomes the norm, then our pain thermostats (or "algostats", as one might call them) are likely to be genetically re-set over time too.

But this recalibration doesn't actually abolish suffering, it just diminishes its prevalence and intensity when physical pain occurs. Moreover, as attested by rare cases of congenital anaesthesia, children born without any capacity to suffer pain are currently liable to undergo all manner of life-threatening medical complications. So does this mean we are stuck with pain in some guise or other for ever?

No, though there are formidable technical challenges to overcome. If we are to abolish physical pain altogether, I think there are two long-term options. These two options are not mutually exclusive, but I will consider them separately. Recall how silicon (etc.) robots with the right functional architecture can get by fine without the nasty "raw feels" of phenomenal pain; they can be programmed to avoid and respond flexibly and adaptively to noxious stimuli. Clearly, there is a distinction between the physiological function of nociception and the subjective experience of phenomenal pain; they are dissociable even in organic robots like us, not just our inorganic counterparts. So likewise, in theory future humans could computationally offload everything nasty or routine onto prosthetic devices, nanobots and the like, preserving only the life-enriching forms of sentience and discarding the ugly Darwinian junk. This is what we may call the Cyborg Solution. The main advantage of the Cyborg Solution in the long run is that it permits maximum lifelong bliss for all sentient life. Thus its ultimate adoption would seem mandatory on a classical utilitarian ethic. But assuming that we don't go down the cyborg route, there is another option. In principle, we can radically reset the scale of the pleasure-pain axis in the mind/brain. All that is needed for an organism to respond adaptively to a changing and potentially hostile environment is informational-sensitivity to fitness-relevant changes - including the binary opposition "wonderful" versus "not-quite-as-wonderful" - regardless of the tidal range of our emotions on an absolute hedonic scale; a narrow compass of pleasure gradients can in theory play a role analogous to pain gradients in some victims of chronic pain syndrome today.

This hypothesis is counterintuitive. One might imagine that if people always feel more-or-less superwell - both physically and psychologically - then they won't be motivated to act circumspectly; and therefore they will tend to hurt themselves, whether physically or emotionally or both. Who could respond adaptively to the world if consumed by a perpetual whole-body orgasm? Yet this doesn't follow. As we know today, the happiest people, the keenest life-lovers, tend to be the most motivated people. It's depressives who tend to be unmotivated. Yes, there are forms of happiness associated with indolence, for example opiated bliss. But there are also forms of happiness associated with intense motivation, forward planning and goal-directed behaviour, so called hyperdopaminergic states. Either way, our descendants, and possibly our elderly selves, will have a choice of what kinds of physical and emotional well-being they want to enjoy, and a choice of what kinds of genetic predisposition to pass on to the next generation. If you don't want to bring any more suffering into the world, then your only option right now is not to have children. In the future, however, we'll be able to have cruelty-free children with a clear conscience - on that score at least.

Gradients of Bliss?
What's true of physical pain and depression is true of other negative states of mind. Thus the prediction that life a thousand years hence will feel orders of magnitude better than now isn't a claim that posthumans will all be uniformly happy, or that future life will be perfect, whatever that might mean. Indeed one can argue that discontent is the motor of progress, and that the functional analogues of discontent are likely to endure one thousand years from now, just as the raw feels of discontent exist at present. Admittedly, it's hard to know whether fourth millennium (post)humans will be endowed with anything even functionally resembling the same core emotions that define our lives today. The molecular signature of some kinds of emotion, for example disgust, panic or jealousy, might be abolished altogether, both phenomenally and functionally, whereas genes and regulatory code for novel life-enriching emotions may be customised and spliced into the genome. Our perceptual and cognitive architecture is likely to be genetically reshaped too - probably in ways beyond the contemporary human imagination. But such innovation isn't essential for an improved quality of life. The functional analogues of anxiety and depression could still persist and yet life could always be subjectively wonderful - since it's technically possible to decouple functional role from the subjective texture of unpleasant experience as we feel it now.

Critically, I'm not arguing that our descendants will enjoy uniform bliss, and certainly not that they will be manic or "blissed out", simply that their genetically constrained floor of comparative ill-being will be higher than our absolute ceiling of well-being. Continual germline-enhancement across the generations will create a novel motivational system. Its mechanisms of emotional homeostasis will transcend the Darwinian pleasure-pain axis. Thanks to the unfolding Reproductive Revolution, there will be continual selection pressure in favour of the biology of a subjectively improved quality of life. Equating net value and net happiness in the manner of classical utilitarian ethics may or may not be simplistic; but acknowledgement of the connection between enhanced value and enhanced emotional well-being is common to a whole range of ethical systems, both religious and secular. Few ethical systems give no weight to emotional well-being. Thus if a piece of music sounds a thousand times more enchanting than its predecessor, or if a work of art looks a thousand times more beautiful to behold than anything physiologically possible at present, then I think the default assumption must be that such overpowering beauty is indeed a good thing - in the absence of cogent arguments to the contrary. The new germinal choice technologies allow the creation of subjectively valuable experience on a truly prodigious scale. So other things being equal, we should embrace their use.

Spiritual well-being?
The approach I've sketched so far probably sounds crudely reductionist. But one needn't interpret superhappiness in just a narrow one-dimensional sense. Take, for example, spirituality and spiritual well-being. ? In future, if you are very spiritual and want to have hyperspiritual children, then you can opt to over- or under-express the relevant genes or allelic combinations promoting a spiritual temperament; and perhaps ultimately design angelic "spiritual" genomes for your children. Indeed if you want to be naturally superspiritual yourself and don't want to take entheogenic drugs, then you could use autosomal gene enhancement and add extra copies or over-express variants of alleles and allelic combinations associated with spirituality. Secular rationalists, on the other hand, may prefer to lay the genetic foundations of a more worldly well-being.

To take another example of multi-dimensional well-being, prospective parents may be able to choose genes and genotypes associated, not just with intelligence in the simple-minded conventional sense, but with an increased capacity for empathy, involving functionally amplified mirror neurons and enhanced social cognition. Prospective parents will have the opportunity to endow their kids with an enriched oxytocin system, leading to greater trust, generosity of spirit, and pro-social behaviour, potentially with immense benefits for society as a whole. Such scenarios are of course speculative.

A Reproductive Elite?

Initially, surely yes. But not for long, even assuming [implausibly] that the world's poorest nations will remain poor indefinitely. Consider how rapidly web-enabled cell phones have spread through even impoverished sub-Saharan Africa. If personal genome sequencing always costs anything like the $200,000 it does now [December 2008; year 2013 = c.$10,000], then only an elite of affluent Westerners could benefit from such breakthroughs. If personal genome sequencing cost ten dollars or less, then effectively everyone can have it. The nature of information and information technology entails that IT-based services don't involve the consumption of scarce natural resources in the way material goods do, where one person's gain is frequently another person's loss. Only a handful of people in the world can ever own a Rolls Royce or a Maserati, and even fewer can own an original Picasso or an Old Master; but an unlimited number of people can listen to the world's entire catalogue of music, enjoy access to all its electronic games, its computer software, its movies, or indeed the whole Library of Congress. Information is effectively free, or at least it will be soon. Later this century, reproductive technologies like preimplantation genetic screening (PGS) and diagnosis (PGD) - techniques used to identify genetic defects in embryos created through in vitro fertilization before pregnancy - are going to become dirt-cheap too. Already crude personal genotyping services are available for a few hundred dollars.

Of course it's easy to sing a happy tune with the word "soon". I'm glossing over a host of problems in the transitional era between old-fashioned sexual reproduction and true planned parenthood. "Soon" in this context may mean decades, and perhaps centuries. But even on the most conservative timescales, we're on the brink of a major discontinuity in the four-billion-year odyssey of the evolution of life on Earth.

Some Unknowns

For the sake of argument, let's suppose that human cloning does eventually become a common mode of reproduction. It's not clear this is a bad development per se, any more than identical twins or triplets are intrinsically bad. Either way, this possibility might seem to throw a big spanner into the argument from selection pressure I'm making here, since genetically identical babies are likely to suffer from the same problems as their father or mother if exposed to a similar environment.

Yet it seems a reasonable assumption that most future human cloners won't seek to create exact genetic duplicates of themselves, but will instead aspire to have offspring free of defects or unwanted characteristics possessed by their parent. To use a trivial example, a human cloner with thinning hair wouldn't necessarily want to have a cloned child with a predisposition to grow bald. Granted, most Asian people who want a clone will want to have children who are Asian-looking, and most blue-eyed people will probably want blue-eyed clones, but presumably carriers of the cystic fibrosis allele won't seek to pass the defective gene on to their cloned offspring. Likewise, for the most part depressive people who might like to clone themselves aren't likely to want depressive children. Cases of "negative enhancement", akin to the existing use of preimplantation genetic diagnosis to select an embryo for the presence of a particular disability such as deafness shared by the parent(s), will presumably be uncommon. So yes, if human cloning becomes widespread, and certainly if human cloning becomes cheap and ubiquitous, then its spread makes the argument from selection pressure defended here more complex; but the practice wouldn't fundamentally undercut its conclusion.

Autosomal Gene Therapy and Enhancement.
Another unknown that adds to the complexity of the selection pressure argument is the future extent of autosomal gene therapy. I've been focusing on reproduction and germ-line gene therapy and genetic enhancement; but somatic gene therapy is sure to become available and probably extensively used too. After all, if offered the choice of either taking a drug to remedy some physical or psychological defect for the rest of your life or curing that deficit with a one-off course of gene therapy, which would you choose - if you were sure that the gene therapy was safe and effective? The same is true of future enhancement technologies - though remediation versus enhancement is a naïve dichotomy.

Potential Pitfalls

The short answer is yes, though I think such scenarios are unlikely. For a start, the totalitarian dictatorships of the twentieth century, not least the Third Reich, all depended on censorship and a state-monopoly of information. The Internet makes the creation of totalitarian dictatorships much harder; as has been well said, the Internet interprets censorship as damage and re-routes. However, this is obviously a huge topic. All I'll say here is that there is a fundamental difference between a regulatory system where eugenics [under whatever name] is practised for the well-being of the individual - whether human or non-human - and an authoritarian society where eugenics is practised for the notional benefit of a class, race or nation.

Even so, there are clearly lots of problems with so-called liberal eugenics. For instance, there are pitfalls with prospective parents choosing enhancements that offer a merely positional advantage to their children. To give a concrete example, if parents pick genes likely to allow their child to grow taller than current average, then there is no net benefit to either the child or society if most other parents do the same. Indeed if human stature were to become significantly higher than today, then we would all be prone to multiple health difficulties under Earth's gravitational regime. Even enhancements such as genes that may contribute to superior intelligence - overexpressing or adding extra copies of the NRP2 or ASPM or microcephalin gene to use a contentious example - that sound as though they could confer intrinsic benefit might arguably amount to positional goods like height. Thus women tend to find intelligence sexy in prospective mates; but presumably what's advantageous to the brainy male bearer in terms of enhanced sex-appeal is relative- and not absolute- intelligence. A counter to this argument might be that there are inherent benefits to high male intelligence aside from attracting women.

In contrast with interventions that confer positional advantage, genetic enhancements that enrich subjective well-being - crudely, whether you are temperamentally happy or superhappy - would be intrinsically beneficial; they can potentially benefit everyone, regardless of where one falls on any comparative scale of well-being. Indeed technologies that biologically enrich emotional well-being are arguably the only enhancements that are intrinsically good as distinct from positionally or instrumentally good. This claim is obviously controversial; it would be contested by many bioethicists who aren't classical utilitarians.

Other pitfalls?
Although designer genomes can in principle lead to vastly greater diversity, might designer genomes lead in practice to greater genetic uniformity - if most parents strive to have similar kinds of "ideal" children, the supernormal reflections of preferences adaptive in our Darwinian past? Admittedly, some kinds of genetic uniformity are presumably desirable. Thus by common consent it would be a blessing if there were no gene for Huntington's disease (HD). But twentieth century eugenicists didn't take account of phenomena such as heterozygote advantage - normally defined as cases where the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype. Heterozygote advantage explains why some kinds of genetic variability persist, most famously the gene for sickle-cell anaemia. Analogous heterozygote advantage may exist for psychological traits too, though this is unproven.

Whatever their evolutionary origin, here are three examples where the issues are complicated.

Calculating Risk-Reward Ratios

If there are likely to be so many possible adverse and/or unintended consequences of the new reproductive medicine - and perhaps dystopian outcomes no one has even considered - then why forge ahead? Why not outlaw the new reproductive technologies altogether, or at least drastically restrict their use to simple Mendelian genetic diseases of the body rather than complex disorders of the mind/brain? After all, there is no way we can computationally model all the ramifications of even modest rewrites of the human genome.

Here the question comes down to an analysis of risk-reward ratios - and our basic ethical values, themselves shaped by our evolutionary past. Lest extension of the new reproductive medicine seem too rashly experimental even to contemplate, it's worth recalling that each act of old-fashioned sexual reproduction is itself an untested genetic experiment, the outcome of random mutations and meiotic shuffling of the genetic deck, and with no happy ending to date. So just who are we to accuse of reckless gambling? As it stands, all of us are genetically predestined to grow old and die; and in the course of a lifetime, the great majority of humans will experience periods of intense psychological distress, for instance loneliness and heartache after an unhappy love affair. Our social primate biology ensures that most of us sometimes experience, to a greater or lesser degree, all manner of nasty states that were genetically adaptive in the ancestral environment e.g. jealousy, resentment, anger, and so forth. Hundreds of millions of people in the world today suffer bouts of depression; others live with chronic anxiety. One might say these phenotypes are part of what it means to be human. Worse, we pass a heritable predisposition to these horrible states on to our children.

Bioconservatives, religious traditionalists, and social reformers alike would contest this bleak analysis. If you believe that human life today is fundamentally good, and viciously unpleasant states of mind are an aberration that can be mostly remedied by improving society, then you will need compelling reasons before wanting to change the regime of ordinary sexual reproduction as it exists now. Most likely, you will be loathe to support anything like the Reproductive Revolution predicted here; and focus entirely on its potential dangers. The spectre of "Brave New World" will probably loom large in any discussion. If, on the other hand, you think that Darwinian life is cruel and tragic by its very nature, then you are more likely to be willing to contemplate radical alternatives to the genetic status quo, despite the possible risks.

My own view of the risks and uncertainties is that there is a critical distinction between trying to abolish suffering exclusively via social reform and abolishing suffering directly via biotechnology. As we know, utopian social experiments typically go wrong, sometimes hideously wrong, and end up causing a lot of suffering instead. The abolitionist project of eradicating the biological substrates of suffering sounds like just another utopian scheme, whether it's touted as a grandiose species-project or simply as a byproduct of the Reproductive Revolution explored here. Although the abolition of psychological pain is arguably no more utopian in principle than pain-free surgery, it could presumably go wrong in unanticipated ways too. Perhaps we'll unwittingly create a fool's paradise. But if and when we ever abolish the molecular underpinning of unpleasant experience, and it becomes physiologically impossible for any sentient being to suffer, we thereby change the very meaning of what it is for anything to "go wrong". Unwelcome surprises where no one gets hurt are very different from unwelcome surprises where they do. For what it's worth, I think the abolition of involuntary suffering is the precondition of any civilised posthuman society; and therefore a risk worth taking.

The End of Sexual Reproduction?

Maybe so. It's a powerful argument. Yet there are strong grounds for thinking that traditional-style sexual reproduction can't continue for more than a few generations. The reason is bound up with the coming revolution in antiaging medicine.

Throughout most of human history, radical life-extension, let alone the prospect of eternal youth, has been the province of quacks and charlatans. To some extent it still is; swallowing a bunch of vitamin pills each day isn't going to let you live for ever. But over the next few centuries, and possibly before, aging and the genes that promote or allow senescence are going be phased out. This is of course a bold claim that I won't even attempt to defend in detail here. If you are sceptical and haven't read the book already, I'd recommend Aubrey de Grey's Ending Aging: The Rejuvenation Breakthroughs That Could Reverse Human Aging in Our Lifetime (2007). Now I am more pessimistic than Aubrey de Grey about timescales. Yet the genetic and pharmacological interventions that we are already trying in nonhuman animals will eventually be tried in the human animal too. One hesitates to embrace what sounds like a facile technological determinism; but I think we can say, quite dogmatically, that if and when radical antiaging technologies become available, then the overwhelming majority of people will use them - regardless of any rationalizations of death and aging we express now. Moreover most people will also want such treatments for their family pets; the Antiaging Revolution won't be confined to one species.

Let's assume for the sake of argument that this is the case i.e. there will be both a Reproductive Revolution and an Antiaging Revolution. If post-genomic medicine dramatically extends lifespan, and fewer and fewer people die of the traditional diseases of old age, then our planet will soon reach its carrying capacity. Looking centuries ahead, a rapidly expanding population of eternally youthful quasi-immortals means that human reproduction of any kind will have to become rare, and eventually a momentous event, and tightly controlled in every respect. It's here that I foresee both the greatest ethical dilemmas arising from the Reproductive Revolution and also the intimate link between superhappiness, superintelligence and superlongevity.

Selection Pressure in an Age of Quasi-Immortality

A counterargument here is that the urge to bear children is under genetic control; and that urge will itself be amenable to biological intervention. Manipulation of our first-order desires is likely to prove biologically easier than defeating aging. Yet if most of one's enhanced fellow citizens do act responsibly and forgo or postpone reproduction, then any predisposition to "cheat" and have children might be highly (genetically) adaptive, at least in the short-run. Such an outcome would be disastrous in an already overpopulated global megalopolis. Plausible group selectionist scenarios aren't easy to construct even for the far future. Hence the price of posthuman superlongevity is the likelihood of ever greater state intervention in the (hitherto) private realm - although such intrusiveness need not be subjectively distressing in any sense we would recognise today, since the functional analogue of distress might suffice. Long before any era of post-genomic medicine, Plato believed that human reproduction should be monitored and controlled by the state, a portent of totalitarian societies to come; but once we transcend the biology of human mortality, some sort of collective control of reproductive decision-making may prove inescapable even in a liberal democracy. The only alternative to such control would be draconian, state-enforced rationing of anti-aging therapies: a scarcely credible re-enactment of Logan's Run. It's important to note that this argument doesn't turn on whether it transpires that the ultimate carrying capacity of our planet is 15 billion, or 150 billion, or conceivably even higher packing densities. Yes, we can colonise the Solar System. In theory, too, in some era of the distant future, the authorities on Earth could tell anyone who wants to have a child that they must do so on one of the extrasolar planetary systems that we colonise. But for the next few centuries at least, and possibly millennia, the prospect of some kind of Galactic adaptive radiation is pure science-fiction. For it is hard to overstate the technical obstacles to mass interstellar travel. Quite possibly posthumans will go to the stars, and perhaps even colonise our local galactic supercluster in a few million years or so. Realistically, this doesn't solve the near-term demographic challenge of a massively overcrowded Earth.

Admittedly I am making a number of contestable assumptions here. I will note just three. First, intelligent life won't wipe itself out altogether in the next few decades. [Doomsday scenarios are conceivable; but they are much harder to construct once self-sustaining colonies are established on other planets later this century.] Second, there is a unique past and a unique future. [This simplifying assumption is inconsistent with quantum cosmology and most likely false. However, consideration of the "branch density” measure of alternative, classically inequivalent histories in post-Everett quantum mechanics would take us too far afield in this talk.] Third, unlike futurists who believe in "uploading", I am assuming that our (post)human descendants will retain an organic substrate - maybe augmented by web-enabled neurochips, nanobots, bionic implants and the like - and hence that humans won't scan, digitize and "upload" themselves to dwell in another computational medium where the constraints of the Earth's ecosystem don't apply. [There is no evidence that your PC is any more conscious than an abacus, despite its greater processing power; and if a souped-up version of your PC contained a digitized representation of you, this would doubtless facilitate restoration from backups, but there are no grounds for thinking such lines of code would be conscious either - let alone "you". Yes, artificial intelligence will hasten the Reproductive Revolution; and perhaps one day we will all become web-enabled cyborgs. And who knows what kinds of exotic postbiological artificial life can be evolved if and when our descendants run mature quantum computers. Yet there is simply no evidence that inorganic systems with a classical von Neumann architecture support "raw feels" or intrinsically matter: the notion that our species might destructively upload ourselves from basement Reality into digital nirvana is unworkable.] So here at least I am being tamely bioconservative in assuming that the Earth 1000 years hence will support a densely populated primordial "meatworld" of our flesh-and-blood post-human descendants.

Anyhow, to summarise, assume that the creation of new quasi-immortal beings will indeed become exceedingly rare later this millennium. The Earth will be (almost) literally full. I'd argue that on such historic occasions as the creation of a new posthuman-being, it is unlikely that superhappy, superintelligent agents will create the genetic malware for unpleasant, stupid, senile substrates of consciousness i.e. archaic Homo sapiens. Our posthuman descendants are more likely to create fellow "smart angels" instead. The triumph of the Reproductive Revolution will have reshaped the post-Darwinian fitness landscape beyond all recognition. Hence my (tentative) prediction that the biology of suffering and senescence is destined to pass into evolutionary history.

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The Reproductive Revolution Selection Pressure in a Post-Darwinian World