A priori knowledge is supposedly independent of experience. I agree with you that we have no evidence of knowledge outside human experience.
But from a scientific perspective, both knowledge and experience arise from the physical properties of the universe; properties that predate humans and biological systems entirely. From that perspective, one could say that all knowledge is a priori.
But whether we say it's all priori or posteriori doesn't really matter. The point is that making the distinction privileges the human perspective in a way that we have no scientific evidence to support. The entire exercise begs the question by assuming that human experience is determinative, or distinct in any way from the rest of the universe.
But from a scientific perspective, both knowledge and experience arise from the physical properties of the universe; properties that predate humans and biological systems entirely. From that perspective, one could say that all knowledge is a priori.
But whether we say it's all priori or posteriori doesn't really matter. The point is that making the distinction privileges the human perspective in a way that we have no scientific evidence to support. The entire exercise begs the question by assuming that human experience is determinative, or distinct in any way from the rest of the universe.