Many people but few caged mice

In my previous post I discussed the study Morals and markets, by Armin Falk and Nora Szech, about the choice between ten euros or the life of a mouse. I will now ask what Partha S. Dasgupta and Paul R. Ehrlich would choose, based on their paper Pervasive externalities at the population, consumption, and environment nexus, published three weeks before Falk and Szech's also in Science.

Both papers are framed around the problem of externalities. Wikipedia defines externality as "a cost or benefit which results from an activity or transaction and which affects an otherwise uninvolved party who did not choose to incur that cost or benefit." I thought everyone else defined externality the same way. Not so. Falk and Szech include "detrimental working conditions for workers" and "child labor" as examples of negative externalities. They are not, according to the common definition, because "workers" and "children" accept the costs of working in exchange for wages. And Dasgupta and Ehrlich include fosterage, which is the practice, common in west Africa, of rearing the children of relatives and friends. Fosterage is not a negative externality of human reproduction, according to the common definition, because foster parents voluntarily accept rearing the children - they ask for it, actually.

The level of an activity that generates negative externalities is higher than is socially optimal. Thus, following their incorrect depiction of fosterage, Dasgupta and Ehrlich claim that there is excessive human reproduction in west Africa. Tellingly, they fail to mention the government subsidies to schooling and children health care in the USA and elsewhere that do contribute to excessive reproduction. And they amply discuss that each person, by degrading productive resources and polluting the environment, inflicts negative externalities on everybody else, but not the fact that people also generate positive externalities, for example by creating new resources for everyone to use productively. After adding up negative externalities and ignoring positive ones, they conclude that there are too many people around. They suggest that Africans spend less on "expensive wedding ceremonies and birth celebrations" and more on condoms ("the unmet need for family planning is substantial").

In Falk and Szech's experimental study, participants chose between money and saving the life of a mouse. A succesful trade between the experimenters and a study subject involved a true negative externality whose victim was the unwilling mouse. Not trading money for the mouse resulted in the mouse being saved. "As a consequence of our experiment, many mice that would otherwise have been killed [gassed] right away were allowed to live for roughly 2 years [in an appropriate, enriched environment, and at a cost]." And Falk and Szech reach a verdict: "There exists a basic consensus that harming others in an unjustified and intentional way is considered as immoral." They consider that allowing mice to live for two years in an enriched environment is better than killing them.

But they fail to mention that keeping mice in an appropriate, enriched environment for two years generates negative externalities. Other organisms will be killed to feed the mice. Subjects who decide to save the taxpayers who fund Falk and Szech's research ten euros are making them pay the expenses of keeping the mouse alive for two years, and are harming the unwilling organisms used to feed it. Furthermore, they are generating environmental externalities associated with rearing those other organisms. Whether this is morally preferable to killing the mouse right away is not clear to me. Is it morally worse to kill the mouse than it is to kill the other organisms? Is having more mice and less tropical forest morally better than the opposite is? Would Dasgupta and Ehrlich, who think that there are too many humans, choose to let the mouse enjoy the gift of life for two more years, at the expense of the lives of other organisms, or would they choose the ten euros?