Peter Singer is one of the most influential and controversial philosophers of our time. Best known for his book, Animal Liberation: A New Ethics for Our Treatment of Animals, Singer is one of the leading intellectuals in the modern animal rights movement, as well as one of our most important thinkers on bioethics, environmentalism and the moral obligations of people living in affluent nations. He is currently the Ira W. DeCamp Professor of Bioethics in the University Center for Human Values at Princeton University and Laureate Professor at the University of Melbourne’s Centre for Applied Philosophy and Public Ethics.

Should the extension of the current life expectancy, for people in the US, be considered a matter of health or a luxury? If the latter, what does it mean to live longer?

I think it's possible to think of it as a health issue and it's possible to think of it as a luxury. But I'd rather say: Is this a good thing to do? And I’d say, other things being equal, yes. How much ought you invest in the resources to do it? Well, clearly less than the cost of saving lives of those who are, say, in their 20s or 30s and could live much longer. But I do think in the long run it would be better if we were able to expand lifespan.

Is extending the life expectancy in the US worthwhile only if it comes alongside advancements that make old age healthier, more fulfilling and less painful?

Definitely. What I'm assuming when we talk about this is there would be something that slows aging. It would obviously depend on how old you are when this develops but instead of progressing, let's say, from the biological 40 to the biological 50 in 10 years you might take 20 or 30 years to do that, and so you'd have more years roughly of the 40 to 50 health state and you'd have more years in the later health stages as well.

Are there some medical means of extending life that you'd consider unethical? 

Obviously you could think of some means of extending life that would pose ethical questions, though I don't know that they're realistically what's being attempted or thought about much at the moment. Things that cause animals to suffer as part of the process, I'd be opposed to that, or those that make humans suffer for that matter. I'd also in general be opposed to putting very substantial resources into extending the lives of people in affluent countries when we could more cheaply extend the lives of people who maybe have a life expectancy of only 50 in developing countries. Any decision that involves spending significant amounts of money is an ethically questionable decision, considering the things we can do in the world with that money. So that will just depend on the cost-benefit ratio of what we're doing.

Jumping off of that, do you believe we can we increase life expectancy in the world without also increasing injustice, especially in regard to the gap between richer and developing countries?

In the short term, I suppose, probably not. Now, when we have so many lives of the global poor that can be very cheaply extended I’d say that ought to be our priority. But in the long run, it may well be that we can make a significant difference to the lives of people in developing countries and at the same time extend the life of people in affluent countries. So it's possible that wouldn't be an injustice if it were done in that way, if we'd already dealt with the low hanging fruit in the developing countries.

When it comes to anti-aging research and treatments, which have the potential to impact everyone on earth, whose moral compass should be followed when it comes to decisions of right and wrong? Who determines what is health and what is mad science?

I think scientists should listen to the debate and be open to the diverse range of viewpoints. But I don't' think scientists should simply say, “Well, 51 percent of the population thinks that this is right and therefore I’ll do it,” or vice versa. I think they should reach their own decisions based on their assessment of the reasons and arguments. Of course, science needs funding and those who fund them might well have a different view, particularly if we're talking about government funding. There's some sort of case in saying that if there's clearly a strong public opinion against this research, that's something that those allocating funding should take into account. But even there, I don't think they're bound to avoid research that a substantial body of the community opposes. If the majority of people feel strongly enough about this, no doubt they'll vote out of office the officials who oversee the funding or they'll insist on laws being passed to stop it.

Do you think it is wrong to genetically modify babies so that they avoid certain mutations and live longer (as described in this article)? 

I don't in principle have an objection to the genetic enhancement of human beings. I think there are many respects in which we could be healthier, more long-lived, and perhaps morally better than we are now and that would be a good thing. Now there certainly would be risks in altering genes in order to achieve that and I think we're a very long way off from that being possible. But I don't in principle think it would be wrong if you could overcome the concerns about how you can avoid other unpredictable adverse consequences.

If people in the US live longer, are they more likely to be concerned about the environment since they will be alive to experience the effects of climate change?

That's a definite possibility. One of the problems now is that the worst consequences of climate change won't affect the current generation of decision makers. It will affect people who are very young now or it will affect their children or their grandchildren.

Is protecting the climate a matter of ethics, or is it a matter of pragmatism? Has it changed over time?

I don't think climate was always an ethical issue. The smoke from the fires of early human beings as they roasted their hunted game did contribute in a tiny way to climate change but they didn't know that so I don't think there was any ethical issue until people actually became aware of this, which really only happened in the 20th century.

You wrote, "The failure of the major industrialized nations to reduce their emissions to a level that will not cause serious adverse effects to others is moral wrongdoing on a scale that exceeds the wrongdoing of the great imperial powers during the era of colonialism." How much are individuals accountable for the impact of those nations?

Clearly not everybody who lives in a nation is responsible for those environmental practices. If you’re someone like Bill McKibben and you've worked very hard to awaken the population of the US to the harmful consequences of greenhouse gas emissions, taken part in protests and written books, then I think it would be absurd to say you are responsible for the practices of the US in terms of its failure to control emissions of greenhouse gases. I think therefore what you have a responsibility to do as a citizen is to be active in changing those practices and one of the ways you can be active is by setting an example yourself. But getting politically active is another way and perhaps more important.

Is it enough to live an environmentally sound life without trying to influence the behavior of others?

No, I don’t think so. The crisis is too serious to say, “Well, my hands are clean. I haven't done this. I live off the grid in a solar heated house.” That's very nice but unless you try to influence other people, your individual efforts are not enough. I think everybody who is aware of the perils of climate change has a responsibility to talk to other people about it to spread this awareness.

You wrote, "We should help today's global poor, but not at the expense of tomorrow's global poor.” How does that apply to climate change?

Well, affluent people ought to be taking the lead here because, firstly, they produce far more greenhouse gases per capita than the poor. Secondly, they can take first steps without any substantial sacrifice. If they tighten their belts a little bit they're still going to be comparatively well off whereas the poor really can't do that. Having said that, I do think the problem is so serious that if a situation arises in which the present poor are hurt by certain political or social measures, but the lack of those measures would be even more injurious to the future poor, those measures are still justified. I do think we need to take account of the wellbeing of future generations, not just present generations.

So should the wellbeing of future generations generally be considered before those of the present?

It is a matter of weighing how much they'll be suffering, discounting for uncertainty, because the further you get into the future the greater the uncertainty becomes about what kind of technologies will have been invented to cope with the problem. But the underlying ethical position is simply that everybody's welfare counts equally if it's in similar kinds of quantities. So we shouldn’t discount the future because this problem is only going to happen in 100 years and it doesn't matter as much as some similar event that might happen tomorrow. I think that's a mistake. But we also shouldn't give any more weight to future generations than we do to our own except for the fact that there are more of them. So it is a tragedy if you're going to render the earth uninhabitable for many centuries in order to avoid some sacrifice by the present generation, because then you're burdening dozens of generations for the sake of the present one.

Some people are resistant to the idea of protecting the environment. How do you rationalize the importance of doing so to those people?

I'm not sure if there's much of anything we can do to change the really recalcitrant people on this issue. It may be that we just have to work to persuade others to form enough of a majority to get things done. Another possibility is that we won’t succeed in getting them to change their mind but the changing climate actually will. It may be that they’ll start to see the problems themselves, and realize the importance of protecting the environment. 

Interview by Jordan G. Teicher.