Babies cry, smile, laugh and react to their environment - so it seems odd to look at a baby and wonder whether or not it's conscious. But consciousness is a tricky thing to pin down, and according to some theories of consciousness, babies don't attain it until two or even three years of age, while others suggest that babies could be conscious even in the womb. It's an important scientific question but also a moral one, as it affects how we treat not only babies but other such "consciousness candidates" as non-human animals, AI and synthetic biological systems.