How did 10gbe happen without increasing the number of wires in the cable?

Question

The ethernet cable speed jump from 100Mb/s to 1Gb/s was possible because all of the wires were put to use in a patch cable. The jump from 1Gb/s to 10Gb/s required no such increase. How did they do this?

Answer 1

See this page for a brief history of Ethernet. Your question infers that you're only concerned about four-pair twisted pair cable, in which case you can search for "8P8C" to see the many different iterations that used the same cable.

In short, the reason for the speed increases is more or less the same as why you can now hold in your hand orders of magnitude more computing power than a desktop computer was capable of ten years ago.