Population ethics and the value of variety

My favorite slogan: Population ethics is aesthetics.

If the people living the future at the time would approve of it, but to you right now it seems awful (e.g. just repeating the same happy hour over and over for eternity), you're totally within your rights to not want that future to happen. Not because of some super-deep further justification, but just because it's okay for you to have preferences about what the future should look like.

Problems in population ethics (are 2 lives at 2 utility better than 1 life at 3 utility?) are similar to problems about lifespan of a single person (is it better to live 2 years with 2 utility per year than 1 year with 3 utility per year?)

This correspondence is formalised in the "Live Every Life Once" principle, which states that a social planner should make decisions as if they face the concatenation of every individual's life in sequence.^[1] So, roughly speaking, the "goodness" of a social outcome $s$, in which individuals face the personal outcomes $p_1,\dots ,p_n$, is the "desirability" of the single personal outcome $p_1▹\cdots ▹p_n$. (Here, $p_1▹p_2$ denotes the concatenation of personal outcomes $p_1$ and $p_2$.)

The LELO principle endorses somewhat different choices than total utilitarianism or average utilitarianism.

Here's three examples (two you mention):

(1) Novelty

As you mention, it values novelty where the utilitarian principles don't. This is because self-interested humans value novelty in their own life.

Thirdly, [Monoidal Rationality of Personal Utility]^[2] rules out path-dependent values.

Informally, whether I value a future $p$ more than a future $q$ must be independent of my past experiences. But this is an unrealistic assumption about human values, as illustrated in the following examples. If $p$ denotes reading Moby Dick and $q$ denotes reading Oliver Twist, then humans seem to value $p▹p$ less than $p▹q$ but value $q▹p$ more than $q▹q$. This is because humans value reading a book higher if they haven't already read it, due to an inherent value for novelty in reading material.

— Aggregative principles approximate utilitarian principles [LW · GW]

In other words, if the self-interested human's personal utility function places inherent value on intertemporal heterogeneity of some variable (e.g. reading material), then the social utility function that LELO exhibits will place an inherent value on the interpersonal heterogeneity of the same variable. Hence, it's better if Alice and Bob read different books than the same book.

(2) Tradition

Note also that the opposite effect also occurs:

Alternatively, if $p$ and $q$ denote being married to two different people, then humans seem to value $p▹p$ more than $p▹q$ but value $q▹p$ less than $q▹q$. This is because humans value being married to someone for a decade higher if they've already been married to them, due to an inherent value for consistency in relationships.

— ibid.

That is, if the personal utility function places inherent value on intertemporal homogeneity of some variable (e.g. religious practice), then the social utility function that LELO exhibits will place an inherent value on the interpersonal homogeneity of the same variable. Hence, it's better if Alice and Bob practice the same religion than different ones. So LELO can account valuing both diversity and tradition, whereas total/average utilitarianism can't do either.

(3) Compromise on repugnant conclusion

You say "On the surface, this analogy seems to favor total utilitarianism." I think that's mostly right. LELO's response to the Repugnant Conclusion is somewhere between total and average utilitarianism, leaning to the former.

Formally, when comparing a population of $n$ individuals with personal utilities $p_1,\dots ,p_n$ to an alternative population of $m$ individuals with utilities $q_1,\dots ,q_m$, LELO ranks the first population as better if and only if a self-interested human would prefer to live the combined lifespan $p_1▹\cdots ▹p_n$ over $q_1▹\cdots ▹q_m$. Do people generally prefer a longer life with moderate quality, or a shorter but sublimely happy existence? Most people's preferences likely lie somewhere in between the extremes. This is is because personal utility of a concatenation of personal outcomes is not precisely the sum of the personal utilities of the outcomes being concatenated.

Hence, LELO endorses a compromise between total and average utilitarianism, better reflecting our normative intuitions. While not decisive, it is a mark in favour of aggregative principles as a basis for population ethics.

— Appraising aggregativism and utilitarianism [LW · GW]

1. ^{^}

   See:

   Myself (2024), "Aggregative Principles of Social Justice [LW · GW]"

   Loren Fryxell (2024), "XU"

   MacAskill (2022), "What We Owe the Future"

2. ^{^}

   MRPU is a condition that states that the personal utility function of a self-interested human $v:P\to R$ satisfies the axiom $v(p_1▹p_2)=v\left(p_1\right)+v\left(p_2\right)$, which is necessary for LELO to be mathematically equivalent to total utilitarianism.

Incidentally, since weights need to be maintained in hardware available for computation, spinning up another thread of an existing person might be 10,000 times cheaper than instantiating a novel person.

Imagine 10 equally happy people, all exactly alike. Now imagine 10 equally happy people, all different. The latter feels more valuable to me, and I think to many others as well.

But their life does seem equally valuable to themselves, so it isn't clear why external evaluations should matter here. Imagine we can either rescue 11 equal people or 10 different people. The equal people would argue that they should be rescued because they are one more.

Are the 11 equal people like a single person who lives 11 times as long as normal and repeats the same experience 11 times while each time forgetting everything that happened before? Arguably no, because the single person would neither want to have amnesia nor repeating experiences, similar to how we wouldn't want to unknowingly die during sleep. But the 11 people are probably not bothered much by the existence of their copies.

Thanks for this - it is one of the reasons I am not a Utilitarian.  I just don't believe that any simple, linear, aggregation function will capture my values (or any human values I've seen in action or can sympathize with), either within a life or across multiple lives.

You get closer when you start talking about declining marginal utility based on "same" or "similar" things - not addition, but logarithmic-ish.  Even so, it's very hard to make that legible and compelling.  It's also not currently allowed to acknowledge that indexical attributes (it matters WHICH human we're talking about) is part of most people's actual value function.