Greater intelligence allows greater introspection, prediction, rumination; allows one to build a model of self and environment not possible at lower intelligence. The suffering that is possible when you can anticipate your death, or imagine a hopeless future, turns otherwise neutral situations into hells.
This is a double edged sword: an animal that is incapable of imagining a hopeless future may also be incapable of understanding that certain terrors it faces are temporary, and thus may live in anguish much more as it has a poorer mental model of its own situation.
This is true, for example I've handled both captive and wild animals naive to humans from the same species (for conservation related research). The captive ones are a bit feisty, but the wild ones are so terrified they are basically in shock and won't move.
Personally, if I have to eat an animal, I'd much rather focus first and foremost on eating the creature that has been killed in as painless, immediate and stressless a way as possible. If choosing between meat options that all have been relatively humanely slaughtered, then I might start to look at other factors such as intelligence or environmental impact of a particular species being raised for food.
That seems like a reasonable heuristic and I understand why someone might feel drawn to put a greater inherent value on intelligent species on an emotional level, but I just don't see the relevance of intelligence in and of itself in terms of ethics.
The problem is harming sentient, conscious creatures. No consciousness, no problem. More consciousness, more problem. Intelligence is not the same as consciousness, but they are highly correlated.
How do you measure that? I mean, both intelligence, emotions, etc. I think your morals are so subjective that will not matter. You should eat animals based on more objective points, like nutritional factor, availability, rather than emotional arguments.
How to measure.. capacity to suffer or intelligence? Both are a active fields of research, the former in the neurobiology, animal welfare, ethology space.
I should add though, I think the science on the nature of sentience and suffering is not quite at a point to support some of the recent proclaimations made on the subject. There's enough there though that I reckon the precautionary principle is defensible though.
Also, to be fair to the people arguing for reducing suffering, doing so can be defended in a entirely rational ethical framework, it need not be an emotional argument. I'm just not sure within that framework how defensible it is to assume intelligence and potential capacity to suffer are correlated for many of the 'higher' animals we eat.
I guess it's a question of when does your moral kicks in and makes you feel bad about the kill.
I've seen and participated both in killing of pig and chicken. Multiple pigs are always a problem that needs to be addressed as they go crazy when they hear the first one die. When you kill a chicken and bleed it out to the ground the other chickens come to pick the blood and totally incapable of realizing the same fate will come to them.
Even lower are insects like a wasp. If you cut its head it will try to eat it then when that fails it grabs it's own head and fly it to home because its second algorithm is called "gather food". I'm not even sure you can call this "intelligence".
I have serious problems killing pigs and I would never attempt one because it feels wrong. But chickens are dumb man, I don't have any problems killing and eating them whatsoever.
