Date of Award


Degree Type


Degree Name

Doctor of Philosophy



Major Professor

John Nolt

Committee Members

David A. Reidy, Jon Garthoff, R. Scott Frey


Human population growth is a contributing factor to a number of significant environmental problems. My dissertation addresses both the negative environmental effects of human population growth and what ought to be done to curtail them. Specifically, I defend two main claims: (1) we have a duty to reduce human population, particularly those of us with large ecological footprints, and (2) morally permissible social policies can satisfy this duty.

I begin by addressing three well-known issues in population ethics that could serve as the basis for objections to reducing population: the Repugnant Conclusion, the Non-Identity Problem, and the Asymmetry. I then argue that we are neither obligated to refrain from procreation altogether nor permitted to procreate as often as we like. This groundwork establishes that the correct view about the ethics of procreation must lie somewhere in the complicated middle ground between these two positions.

After surveying the environmental harms caused by rising human population (focusing in detail on effects caused by climate change and biodiversity loss), I argue that we have a collective duty to reduce human population in order to avoid causing catastrophic harm to future people. While we should attempt to reduce environmental degradation by reducing our rates of environmentally harmful consumption, it is not possible to do so rapidly enough to avoid environmental catastrophe: we must reduce human population as well.

I then discuss the policies that might be implemented in the near term to slow population growth and whether these policies could be implemented in ways that are not profoundly unjust or otherwise unethical. I also argue, on the basis of maintaining moral integrity and taking the harms of overpopulation seriously, that couples generally ought to avoid having more than two children even in the absence of policies incentivizing this behavior and even when they live in parts of the world where their individual ecological footprints are relatively small. I close the dissertation by highlighting some of the lingering questions that will have to be answered in future research on this subject.

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