Here is a picture of the wings of the A340 (launched in the late 1980s) and the Boeing 747-200/400 (launched in the early 1970s / 80s) superimposed upon each other (source: https://www.amazon.com/Evolution-Airliner-Ray-Whitford/dp/186126870X).
I was hoping to use this image to inquire about technological improvements in wing design between 1970 and 1990. The reason for the comparison between these two airliners in particular is that they seem as close to a "fair" comparison that can be made between airliners over very different time periods, specifically because they're designed to carry relatively the same amount of people.
Specifically, there were two facts about the wing planform that I wanted to ask about.
Greater aspect ratio. The A340 has a much greater aspect ratio because it has the same span but much lower total wing area. This improved the L/D ratio by reducing induced drag. What allowed engineers to use a higher aspect ratio wing for the A340? I.e., could the engineers at Boeing in the late-1960s have designed a plane with the same aspect ratio as the A340 if they wanted to (in which case, the higher aspect ratio on the A340 was a design choice, and not a result of any improvement in techniques, methods, materials etc.).
Less wing sweep. Wing sweep is desirable because it lets you fly faster without incurring extremely large drag penalties (increases critical mach number), but it does so at the expense of lift. Therefore, if you can get away with a lower sweep angle for a given speed, that's something that would be good for fuel efficiency. How were engineers able to get away with reducing the wing sweep of the A340 while having it fly at generally speaking, the same cruise speed as the Boeing 747?
Thanks so much!