It's the peak of hubris to assume that human brains are the only way to attain intelligence. At the very least there probably are or have been other forms of intelligence with a different biological structure on other planets, and it may be possible to build a similar artificial structure in future with sufficient complexity to allow intelligence to emerge.

Our current machines are IMO nowhere near general intelligence and consciousness. However I don't think that means we can discount substrates other than neurones for intelligence in future. There is no evidence that you could not in theory build an intelligence using a different substrate than human brains.