it turns out that saving people by hastening the arrival of LEV wouldn't prevent births and could actually increase the average fertility rate of the world. This leads to a counterintuitive result: Aging research could be even more valuable under the impersonal view of population ethics.

The sense of 'even more valuable' meant here seem to be something like 'more adjusted morally relevant QALYs.' But a total view of population ethics (contrasted with a symmetric person-affecting view) generically massively increases the potential QALYs at stake, and shifts the relative choiceworthiness of different options, so that on the impersonal view life extension is less valuable compared to the alternatives (and thus less of a priority for actual efforts) even if more important in absolute terms:

• Because animal populations turn over extremely rapidly and our interventions generally take too long to help current animals (only changing the conditions of future generations), the impersonal view vastly amplifies the relative importance of helping them relative to long-lived humans
• Considerations of existential risk for future generations potentially affect populations many orders of magnitude larger than current human populations (and most of those generations will in any case have access to life-extension), so the total view strongly favors interventions that yield QALYs through effects on long run civilizational trajectories or survival, rather than effects like those from medical life extension
• Life extension may help affect distant future generations, and fertility boosts increase growth, but doesn't seem very well-targeted to that task

So I think the counterintuitive result is counterintuitive because it's not asking the right (action-guiding) question, and in action-guiding terms the person-affecting view does much more strongly favor life extension.

One question I have about these discussions is that I'd read some arguments back when I took a class on environmental science that humanity was near the earth's carrying capacity, meaning there is not capacity on earth for a much larger population (and capacity is quite likely smaller). This term "carrying capacity" seems like a sketchy one that tacitly packs in normative and positive judgments, so I don't endorse it, but is there a chance that something like this is true, and so lengthening life will reduce the probability of others being born because it raises the probability of environmental problems that lower the sustainable population?

Good post. Some further considerations on the total view side of things (mostly culled from a very old working paper I have here where I suggest life extension may be bad - but N.B. besides its age and a few errors, my overall view is now tentatively pro rather than tentatively con).

0. LEV or not seems to be a distraction. The population ethics concerns don't really change much either way if the offer on the table is LEV or merely 'L' (e.g. there's a new drug which guarantees lifespan to 150 but no more).

1. As the contours of your argument imply, I think the core ethical issue on totalist-y lights would be whether there is a 'packaging constraint' on how one should allocate available lifetime to persons (e.g. better 1 800 year life versus 10 80 year lives, or vice versa), versus a broad cloud of empirical considerations and second order effects (although I think these probably dominate the calculus).

2. I don't buy the story that life extension can be a free lunch. If it is better to 'package' lifespan into 80 year chunks versus millenia-sized chunks, whether or not to pursue this will have great impact across the future, so any initial 'free benefit' will be probably outweighed by ongoing misallocation across the future. (I suppose the story could be 'LEV, even if bad, is inevitable, and doing it sooner at least gets a bigger free lunch - but it seems in such a world there bigger scale problems to target).

3. On pure aggregation, the key seems to be whether lifespan has accelerating or diminishing marginal returns. As you say, intuitive survey by time-tradeoff gives conflicting recommendations: most would be averse to gambles like "Would you rather 5% chance of 2000 years (and 95% of dying right now) versus keeping your life expectancy?", yet we'd also be averse to 'Logan's run' (or Logan's sprint) cases of splitting 80 year lives into 16 5-year lives (or, indeed, millions of 2 minute ones).

3.1 One natural reply to defuse 'Logan's run' type reductios is to suggest it is confounded with human development. One might say our childhood and adolescence is in part an investment to enjoy the greater goods of adulthood. So perhaps we would take lifespan to have accelerating returns up commensurate to this, but maybe not for the interval of 20-ish to infinity (so if the returns diminish, there will usually be a break-even point whereby the 'investment cost' is matched by the diminishing returns loss, so making the ideal tiling of lives across time not 'as long as possible'.

(We should probably be pretty surprised if the morally 'optimal' lifespan just-so-happened to match our actual lifespan which emerged from a mix of contingent biological facts. Of course, it could be the 'optimal' lifespan is shorter, not larger, than the one we can typically expect.)

3.2 There's a natural consideration for diminishing returns on the idea that people may naturally prioritise the best things to do with their life first, and so extending their lives gives them opportunity (borrowing a bit from Bernard Williams) to engage in further projects which, although good, are not as good as those they prioritised before then. So packaging into smaller chunks offers the ability for the population over the time to complete more 'most valuable' projects.

3.3 On the other, there's a murkier issue about maybe having a much longer life 'unlocks' opportunities which are better than those shorter lives can access. In the same way 'living each day as your last' when taken literally is terrible advice (many things people want to do take much longer than a day to accomplish), perhaps (say) observing changes over cosmological or geological timescales are much experiences than what one can do in decades. This looks fairly speculative/weak to me.

What seems more persuasive on the 'increasing marginal returns' side is the idea of positive interaction terms between experience moments. Some good things could be even better if they resonate with other previous moments, and so a longer prior life seems to provide further opportunity for this (e.g. insofar as 'watching the grandchildren grow up' is joyful, a longer life better ensures this occurs, among many other examples).

4 Egalitarianism, 'justicy'-considerations, or prioritarianism will generally push towards packaging in shorter blocks rather than longer ones: the one which best gets around tricky different number cases is prioritarianism. Insofar as you are sympathetic to these views, these will seem to push against life extension.

4.1: I'm pretty sympathetic to Parfitian/deflationary accounts of personal identity, which would take the wind out of the sales of this line of argument (as there isn't much remaining sense of a given person being better or worse off than another, nor of an index to which there's a 'you' that accrues person moments which may have diminishing returns). Such a view also takes the wind out of the sails of a pro life extension case (as we should be relatively indifferent to whether future moments are linked to our present ones or otherwise), although there might be second order considerations (beyond those mentioned above, if most experience moments simply prefer to be linked up to more future ones, this is a pro tanto consideration in favour).

5 It seems the second order impacts are best distinguished from the 'pure axiological' issue above. It could be that very long lives are an imperfect allocation, but still best all-things considered if (for example) it allows people to develop much greater skill and ability and (say) produce works of even greater artistic genius. A challenge to trying to disentangle this is plausible scenarios which offer (radical) life extension likely involve other radical changes to the human condition: maybe we can also enhance ourselves in various ways too (and maybe these aren't seperable, so maybe the moral cost we pay for improperly long lives is a price worth paying for the other benefits).

5.1 If we separate these and imagine some naive 'eternal (or extended) youth' scenario (e.g. people essentially like themselves, with a period of morbidity similar to what we'd expect now, but their period of excellent health extended by a long time), I'd agree this leans positive. Beyond skill building benefits, I'd speculate longer lives probably prompt less short-sightedness in policy and decision making.

I think it's an interesting cause area (upvoted for investigating something new), though I have three important quibbles with this analysis (in ascending order of importance):

1) The person-affecting (PA) view doesn't make this a slam-dunk. PAness doesn't signify that death in itself has negative value, so given your assumption 'that there isn't suffering at the end of life and people get replaced immediately', on the base PA view, increasing lifespans wouldn't in itself generate value. No doubt there are flavours of PA that would claim death *does* have disvalue, but those would need to be argued for separately.

Obviously there often *is* profound suffering at the end of life, which IMO is a much stronger argument for longevity research - on both PA and totalising views. Though I would also be very wary of writing articles arguing on those grounds, since most people very sensibly try to come to terms with the process of ageing to reduce its subjective harm to them, and undoing that for the sake of moving LEV forward a few years might cause more psychological harm than it prevented.

2) My impression is that the PA view is held by a fairly small minority of EAs and consequentialist moral philosophers (for advocates of nonconsequentialist moral views, I'm not sure the question would even make sense - and it would make a lot less sense to argue for longevity research based on its consequences), and if so, treating it as having equal evidential weight as totalising views is misleading.

It's obviously too large a topic to give much of an inside view on here, but if your view of ethics is basically monist (as opposed to dualist - ie queer-sort-of-moral-fact-ist) I don't think there's any convincing way you could map real-world processes onto a PA view, such that the PA view would make any sense. There's too much vagary about what would qualify as the 'same' or a 'different' person, and no scientific basis for drawing lines in one place rather than another (and hence, none for drawing any lines at all).

3) 'Reminder: most of the impact of aging research comes from making the date of LEV come closer and saving the people who wouldn't otherwise have hit LEV.'

This is almost entirely wrong. Unless we a) wipe ourselves out shortly after hitting it (which would be an odd notion of longevity), or b) reach it within the lifespans of most existing people *and* take a death-averse-PA view, the vast majority of LEV's impact of it will come on the ripple effect on the far future, and the vast majority of its expected impact will be our best guess as to that.

EAs tend to give near-term poverty/animal welfare causes a pass on that estimation, perhaps due to some PA intuitions, perhaps because they're doing good and (almost) immediate work, which if nothing else gives them a good baseline for comparison, perhaps because the immediate measurable value might be as good a proxy as any for far-future expectation in the absence of good alternative ways to think about the latter (and plenty of people would argue that these are all wrong, and hence that we should focus more directly on the far future. But I doubt many of the people who disagree with *them* would claim on reflection that 'most of the impact of poverty reduction comes from the individuals you've pulled out of poverty').

Longevity research doesn't really share these properties, though, and certainly doesn't have them to the same degree, so it's unlikely to have the same intuitive appeal, in which case it's hard to argue that it *should*. Figuring out the short-term effects is probably the best first step towards doing this, but we shouldn't confuse it with the end goal.