Data was a technical advance to Next Generation, wasn�t he?

In the original series we would occasionally see androids. There was an episode called I Mudd that was about this rather shady character named Harry Mudd who had stumbled upon this race of androids. Their creators had long since departed and these androids were essentially directionless until he arrived and started turning them toward his purpose. But they were very bland, dry, almost thoughtless automatons. They could respond, they could react, they looked like people, they sounded like people. But there was no sense of anything really going on behind the eyes.

Commander Data was much more sophisticated. He was also an android, but he was capable of independent thought. He was sentient and he had consciousness, so that was clearly a technology far beyond the technology that was available to humans or the original series.