Sadly, it turns out I misread Russell Blackford's article, and we aren't really to think of the life extension drug as costing users a reduction in offspring. Boo hoo, because I thought it was awfully fun contemplating whether it's worth giving up life-creation for life-prolongation. I was working myself into a nearly Catholic fervor about the beauty of making new people.
No, what's going to happen is that in the 150 scenario, population will be halved fairly naturally, since people will have on average 2 kids in the first 75 years, but won't reproduce in the second 75 years. In the usual 75 scenario, people would have 2 kids per 75 years of life. So there are indeed half as many people in 150 but not because people have traded away one kid for a longer life.
Apologies to Russell for messing that up! Now let's see what else I can mess up. (I wish I could just give you the pdf, but that would be a no-no.)
Blackford and Singer both assume 150s have lower average happiness than 75s because of a bit of post-75 age-related decline. We can stipulate that it's 4.5 in 150, but 5 in 75. Still, the total amount of happiness for a 150 is greater (675 units) than for a 75 (375). They both think this makes 150 the better life, a claim you could debate, even given those numbers (see Robert Nozick's book The Examined Life for objections), but let's go along with it. If 150 is the better life, isn't it obvious that the researchers should develop the drug?
No, says Singer. We have to do all the math. Using Blackford's numbers--
75 world: 375 happiness units X 2 billion people = 750 billionSinger says we should stick with our 75 world because there's more total happiness. Blackford says this is misguided, and we should pursue the 150 world.
150 world: 675 happiness units X 1 billion people = 675 billion
There's way too much in the article and in the voluminous associated literature to explain the reasoning on both sides, so I'm going to pluck out just one issue. The lower total in 150 is because of the missing happiness of non-existent people. Deciding what to do based on totals effectively attaches importance to them. Blackford thinks their good doesn't matter, since they're merely possible. Thus, we shouldn't decide what to do based on totals. (He also makes a rather different argument that turns on Parfit's "repugnant conclusion," but I'm going to sidestep that whole kettle of fish.)
Here's a thought experiment he offers to convince us that the total approach is wrong. A benevolent (but not all powerful) god must choose between two worlds he could create:
Planet A: 1 billion people each enjoy a total of 6 (out of 10) units of happiness over their lives. Total: 6 billion units of happiness.It would be really daft if the god created planet B, right? So deciding based on totals must be wrong. Doing so effectively gives weight to the missing happiness of non-existent people, and that's as misguided as it sounds.
Planet B: 6 billion people enjoy a total of just 1.5 units of happiness over their lives. Total: 6.5 billion units of happiness.
OK, so far it seems like Blackford is right. But is he? Singer defends the total view in Practical Ethics by noting how it does make sense to give weight to the non-misery of non-existent people. To see his point, think about that god again. Now he (she?) is faced with a choice between creating more miserable people or fewer miserable people.
Planet C: 1 billion people all suffer constantly, each experiencing a total of 10 units of misery over their lives. Total: 1 billion units of misery.Clearly the god should create Planet C, just as the total view says. It's not misguided at all to effectively take into account the missing misery of the people who don't exist on Planet C.
Planet D: 2 billion people all suffer constantly, each experiencing a total of 10 units of misery over their lives. Total: 2 billion units of misery.
If the total approach where misery is concerned is correct, then how can the total approach where happiness is concerned be wrong?, Singer asks. This strikes me as very good question.
Some of the worry about the total view comes from what I take to be a mistake about what it leads to. If you take the missing happiness on planet A to be bad, does that mean we all have an obligation to create as many children as we can? Do we have to "rescue" non-existent children and bring them (and their happiness) into existence?
No, because there's nothing that says there aren't better ways for me to increase total happiness.
Take, for example, the very wonderful Paul Farmer, described in Tracy Kidder's very wonderful book Mountains Beyond Mountains. By working in a Haitian hospital and starting innovative health services around the world, he has saved thousands and thousands of lives. He has just one child. It would be daft to think that the total view enjoins us to complain that he didn't have more children.
In our overpopulated world, there's a very real question whether adding more children does increase total happiness. The child's happiness has to be taken into account along with the impact produced by her coming into existence. It's really the person who wants to have children, not the person who doesn't, who has to work hard to come up with a justification.
But now suppose we mess up the world terribly, and wind up with an utterly bleak scenario like the one in Cormac McCarthy's book The Road. All animal life has been wiped out, and there are just small numbers of humans trying to eke out their survival. So all that is good in sentient lives is at risk of disappearing. In that world, is there an obligation to make sentient life--like human children, for example? I don't find it counterintuitive to say so. And the obligation doesn't seem to really be about perpetuating a particular biological species, as opposed to creating happy individuals.
So--because of the misery argument, and because I don't think the total view leads to absurd claims about who ought to have more children, I'm casting my vote with Singer.
I've sidestepped a lot of other arguments in Blackford--but writing this much is cruel and unusual enough. Final footnote for the perplexed: all these issues are relevant to huge numbers of questions in animal ethics, reproductive ethics, and environmental ethics. Reading Practical Ethics is a pleasant way to find out the relevance, while reading Parfit's Reasons and Persons is a much more toilsome sine qua non.