Marked. Wow! Nice work! I would have fallen back on circular reasoning too, just a couple years ago.
However, the best thing you did, which is what I think makes the difference, is that you challenged them to research and prove the correct answer, to themselves. I often think about how when I pioneered, no one at the door, ever honestly explained their belief or politely challenged us to prove them wrong on this subject. I really feel this is why it's important for people to not just politely dismiss JW's, but have a calm, sensible question that makes them curious and pricks their brain.
Everyone is different, but personally this would have sent me home to research, just so that I didn't appear ignorant. Nowadays, this particular subject coming up and being challenged would send a person (more so the younger JW's, who use the internet for schoolwork) straight to the computer first to research. In the U.S., evolution seems so misunderstood by many of us and it's disturbing how religion, not just JW's, can hold us back from progress.