Why would the chicken have to learn to follow the ethics in order for its interests to be fully included in the ethics? We don’t include cognitively normal human adults because they are able to understand and follow ethical rules (or, at the very least, we don’t include them only in virtue of that fact). We include them because to them as sentient beings, their subjective well-being matters. And thus we also include the many humans who are unable to understand and follow ethical rules. We ourselves, of course, would want to be still included in case we lost the ability to follow ethical rules. In other words: Moral agency is not necessary for the status of a moral patient, i.e. of a being that matters morally.
The question is how we should treat humans and chickens (i.e. whether and how our decision-making algorithm should take them and their interests into account), not what social behavior we find among humans and chickens.
Hi all, I’m a lurker of about two years and have been wanting to contribute here and there—so here I am. I specialize in ethics and have further interests in epistemology and the philosophy of mind.