Those who claim that artificial intelligence will be conscious by mid-century seem to brush aside the fact that we know very little about consciousness.
We also know very little about the origin of the human brain. Take this controversy about why the large human brain evolved:
One of the most prominent explanations for the evolution of big brains is that large social groups lead to problem-solving challenges, which in turn create an evolutionary pressure for smart, big-brained individuals capable of navigating social situations.
But later research linked primate brain size to environment, territory size, and diet instead of size of groups. Then the focus returned to the neocortex, thought to be responsible for higher intelligence functions. One group focused on forty primate species:
The problem is that the data set is skewed in some very important ways—it focuses more on “Old World” African and Asian monkeys, says Shultz, and less on the “New World” monkeys of the Americas. Among those Old World species, there’s a heavy emphasis on the fruit-eaters. Powell also points to a lack of good data on great apes, like gorillas and orangutans, in the data set.
It’s possible that the neocortex correlation shows up because the skew in the data coughs up a false positive. It’s also possible that it’s real. Cathleen O’Grady, “The evolutionary mystery of gigantic human brains” at ArsTechnica
So we don’t know. And we haven’t even got to the human brain yet.
When we do turn to that topic, we find that many researchers have quite a different take on the evolution of human brain size: It may be a handicap or else doesn’t matter. See, for example,
Human evolution researchers: Social challenges decreased brain size
Did large brains cause Neanderthals to go extinct?
Homo naledi’s small but sophisticated brain challenges belief in “an inevitable march towards bigger, more complex brains.”
Human origins: The war of trivial explanations