Does comparing the total number of human neurons vs. the total number of neurons among all domesticated animals affect the moral balance between animals and people? Oxford philosopher and Effective Altruism co-founder William MacAskill engages in such neuron counting as he grapples with the issue of the moral standing of animals compared to people in his new book What We Owe The Future. I was unable to include an investigation into his ruminations on this topic in my forthcoming review of his book in Reason's December 2022 issue, so let's take a look here.
First, just how many animals are we talking about? According to MacAskill's count, people slaughter and eat 79 billion vertebrate land animals annually. The amount of biomass in land-based farm animals is 70 percent greater than that amassed in all humans. And domesticated food animals outnumber us substantially. At any one time, some 25 billion chickens, 1.5 billion cows, 1 billion sheep, and 1 billion pigs are alive. And there are 100 billion farmed fish as well. Given the rate at which these animals are bred and raised for slaughter, humans annually eat about 69 billion chickens, 300 million cows, 600 million sheep, and 1.5 billion pigs. MacAskill notes the poor factory-farming conditions under which many of these food animals are raised, resulting in, he argues, a "society-wide production of a monstrous volume of suffering." (He does not count cats and dogs, 600 million and 700 million respectively. Possibly because the lives of Fluffy and Fido are pretty plush compared to those of food animals.)
MacAskill observes that "the question of what weight to give human interests and to nonhuman animal interests is difficult." With respect to these moral difficulties, he points to analyses done at Rethink Priorities by fellow effective altruist philosopher Jason Schukraft. Among other considerations for assigning degrees of moral status to creatures, Schukraft says, is their capacity for welfare, or how good or bad an individual's life can go.
In a rough attempt to "capture the importance of differences in capacity for wellbeing," MacAskill suggests that we weigh "animals' interests by the number of neurons they have." Beetles, with just 50,000 neurons, have little capacity for well-being, whereas chickens, with 200 million neurons, have a considerably greater capacity for welfare. By comparison, humans have 80 billion neurons. When comparing total numbers of neurons, MacAskill calculates that "humans outweigh all farmed animals (including farmed fish) by a factor of thirty to one."
"If we allow neuron count as a rough proxy," observes MacAskill, "we get the conclusion that the total weighted interests of farm land animals are fairly small compared to humans, though their wellbeing is decisively negative." However, the number of neurons in wild fish outweighs that of humans by a factor of 17. On the other hand, MacAskill suggests that it's hard to tell if most wild fish, especially prey fish, experience anything like positive well-being. Ultimately, MacAskill recognizes that nature's "circle of life" is, indeed, "red in tooth and claw," so that it is not at all clear "whether wild animals have positive wellbeing or not."
Counting neurons aside, it is the distinctive agglomeration of human neurons that, as far as we know, makes moral reflection of this sort possible.