Inner speech and consciousness are not the same thing.
We are (almost) all familiar with the voice that is always going on in our heads. It is variously called our inner voice or inner speech or our inner dialogue. It seems to be inseparable from our sense of self. That is, it seems to be me. Yet there is a tiny number of people without inner speech. This condition has been called anauralia. Little is known about it. Thanks, though, to Jill Bolte Taylor, we do have an account of it. As a result of a stroke in 1996, she was left without inner speech for five weeks. She described the feelings she had during that time as ‘blissful’ and ‘untethered’. The point is that she had feelings. She remained conscious in the sense of continuing to possess consciousness. She was just not conscious of any of the words that might have been produced by the language processing areas of her brain. Perhaps early humans who possessed consciousness began to develop language but had not at that point developed inner speech. Were that to be the case, then all humans at that point would have been anauralics.
You might also like to browse other language posts: https://www.thesentientrobot.com/category/language/