[EDIT: No longer confident in this post, see edit note at bottom. May formally partially-retract it later.]

Yesterday's post reviewed research showing that animals' intelligence seemed correlated with their number of cortical neurons. If this is true, we could use it to create an absolute scale that puts animals and humans on the same ladder.

Here are the numbers from this list. I can't find chickens, so I've used red junglefowl, the wild ancestor of chickens. I can't find cows, so I've eyeballed a number from other cow-sized ruminants (see here for some debate on this).

Some animal rights activists discuss the relative value of different species of animal. You have to eat a lot of steak to kill one cow, but you only have to eat a few chicken wings to kill one chicken. This suggests nonvegetarians trying to minimize the moral impact of their diet should eat beef, not chicken. But any calculation like this depends on assumptions about whether one cow and one chicken have similar moral values. Most people would say that they don't – the cow seems intuitively more "human" and capable of suffering – but most people would also say the cow isn't infinitely more valuable. Different animals rights people have come up with different ideas for exactly how we should calculate this.

I wondered how people's intuitive ideas about the moral value of animals would correspond to their cortical neuron count. I asked Tumblr users who believed that animals had moral value to fill out a survey (questions, results) estimating the relative value of each animal, in terms of how many animals = 1 human. Fifty people answered, including 21 vegetarians and 29 nonvegetarians. Their numbers ranged from 1 to putting their hand on the 9 key and leaving it there a while, but when I took the median, here's what I got: