There's no biological structure the creates consciousness to the ppint where you can say "if you have x, you're conscious", to the point where saying "humans are conscious" or even "only humans are conscious" aren't always true. Many elephants are conscious. Some dogs are consciohs. Some humans aren't. And no, the split between humans are/aren't conscious ARE NOT CORRELATED WITH DEMOGRAPHIC (fuck Nazis and racists), nor is it easy to draw a line in the sand because it's a spectrum.

It comes from having a brain that's complex enough. Decision making process start interacting together in unexpenced ways, with subtle variations caused by genetics and history. Literally just read the wikipedia page the previous person posted and apply that same logic to brains and minds.