> The only reason why animal consciousness has been controversial historically is a religious one—the Bible has typically been read as placing humanity in a category of its own.

Did you just make this up? Because it's obviously not true. And you conflate two concerns, namely, "having consciousness" and "placing humanity in a category of its own".

First, you don't see denial of consciousness in other animals in the ancient or medieval world. If anything, it is much more natural to conclude other animals are conscious based on observation than it is to deny consciousness. Even today, I don't know anyone who denies animals are conscious. Everyone treats their pets, for instance, as conscious beings, because they are. Now, people also anthropomorphize animals, sure, but there's a difference between the two degrees of attribution. Attributing consciousness is far more conservative than attributing human qualities in an equivocal way.

Take Aristotle's De Anima, for example, in which he analyzes the varieties of life according to the kind of "soul" each possesses, and such that each higher soul entails the powers of all the lower souls. The three kinds he identifies, ordered from lowest to highest, are the nutritive soul, characteristic of plants; the sensitive soul, characteristic of animals; and the rational soul, particular to human beings. Even here, we can see both a certain uniqueness to human beings alongside what you might call the consciousness of animals by virtue of the sensitive soul. What differentiates human beings from all the animals is not that they are conscious, but that they are rational.

Second, where the Bible is concerned, I have no idea where you get the idea that it claims other animals lack consciousness. Consider just these two passages from the Old Testament:

Genesis 9:2-3: "The fear and dread of you will fall on all the beasts of the earth, and on all the birds in the sky, on every creature that moves along the ground, and on all the fish in the sea [...]"

Do you see any mention of rocks in this verse? Do things lacking consciousness live in fear?

Proverbs 12:10: "The righteous care for the needs of their animals, but the kindest acts of the wicked are cruel."

I suppose you could be kind to an unconscious living thing in the sense that can act for its objective good, but it seem a little strange to speak of animals in this way, but not plants, if animals are as unconscious as plants.

Now, yes, human beings are recognized as different from the other animals as early as Genesis, having been created in the image of God, which has to do with a relation of analogous similarity with God, where human beings are understood as personal creatures possessing rational intellect and free will ("analogous" cannot be stressed enough; the infinite God is very much unlike any created being, and so any similarity can only be analogical; see the analogia entis). However, it does not follow that the other animals lack consciousness. The ancients and medievals would find this claim ridiculous.

If you want to know where the denial of consciousness in other animals began, you can thank modern thinkers like Descartes, who posited that the universe is composed of two kinds of things, res extensa and res cogitans. Res extensa is merely extension in space, while res cogitans is the seat of thought, sensation and thus consciousness. According to this anthropology, of the animals, only human beings are a composite of both, and so only human beings are capable of consciousness. The angels are res cogitans, while the other animals are mere res extensa. In other words, according to Descartes's mechanistic worldview, animals are effectively insensate machines.

And so this is a recently development in history, very much occurring within the ferment of modernity. Materialism also finds its roots in Descartes, not because he was a materialist himself, as he admitted the existence of res cogitans that is not reducible to res extensa, but because he framed things in those terms. Materialists, operating within those parameters, reject the existence of res cogitans, instead claiming that all that has been attributed to res cogitans is reducible to res extensa. Of course, it isn't (e.g., the problem of qualia, or the problem of intentionality), which is why materialism was stillborn, but now transmuting into preposterous things like eliminativism among a stubborn remnant of believers.