The original idea was to have the first pair in the middle, the next pair outside of that, etc.. so that a smaller pair plug could fit in a larger sized jack.

The original idea was to have the first pair in the middle, the next pair outside of that, etc.. so that a smaller pair plug could fit in a larger sized jack. However when it came time to specify the pinout when designing ethernet over utp they found the separation required to place the wires like this was too great and degraded the characteristics of the line so they placed a pair on each side keeping the center as is for some sort of compatibility. Like said you could have a phone line in the center of your ethernet. suck to be you it you did that then later wanted to upgrade to gigabit. It also suck if you had some idiot doing the wiring who had the bright idea "herp derp, two pairs of this are not used... I could run two ethernet lines over this cable" Which is sort of my next complaint, tia-568, the intent was to have the A standard be used with the B standard for compatibility with existing phone lines . Every place I have ever been they just used the B standard. I mean it is not a huge deal, but it always bugged me. https://en.wikipedia.org/wiki/ANSI/TIA-568 https://en.wikipedia.org/wiki/ANSI/TIA-568