The development of human self-awareness and consciousness is a complex, ongoing topic in science. While there's no definitive answer, researchers have found evidence that suggests early forms of self-awareness emerged around 1.5 million years ago with Homo erectus. However, the full development of modern human consciousness, including abstract thinking and language, likely occurred between 200,000 to 70,000 years ago with the emergence of Homo sapiens.
Pro tip: The exact timeline is still debated among scientists, as it involves interpreting archaeological and fossil evidence, which can be challenging and subject to new discoveries.