Each key is a little different. None are tuned to mathematical perfection, because that makes use of more distant keys impossible, with strident harmonic relationships that are in a word, hideously ugly. OK two words. 

c minor is more serious than d minor. d minor is more evil than f minor. g minor is darker than a minor. Keys are chosen for their ability to generate the desired mood or feeling. Along with that are inseparable tempi and dynamics. Harmony may be vertical or linear, or both. Harmony and rhythm produce movement. 

G major is not as bright as A major. #F major is glaring bright- so much so its almost overexposed. 

C is the original key. Do in the world of solfege. 

Do re mi fa sol la si Do. America uses ti for si. Rest of world uses si. 
America moves Do around. Rest of world fixes Do to C. 

When notation was written down on paper, originally there was one line. That was C. Numes above it were higher, and numes below it were lower. Wasn't very accurate. How much higher and lower was left to the singer or player. Realization that voices sing in different registers led to a treble line for high voices, and a bass line for low voice. Average voices had the C line. The treble line was G, and the bass line was F. The fifth above and fifth below C. 

Guido, a monk conducted using his five fingers, pointing to the finger or space in between. By putting five lines on paper for the five fingers, notation became more accurate. They put a mark on the middle line to indicate C, or Do. 
As instruments and voices went higher and lower, composers added lines to the top and bottom, until the staff had 11 lines. It was impossible to quickly read what any note was. 

Somebody discovered the human eye and mind can see up to five lines all at once. The original staff had five lines. By removing the middle line of the awkward 11 line staff, that left two staves of five line each. Composers put a fancy letter G on the upper one, spiraling around the line G, the original high voice line. They put a fancy letter F on the lower staff, curled around the line F. Treble clef is also called G clef. Bass clef is also called F clef. 

The movable C clef establishes middle C. Middle C is not the middle of the piano. It is the middle of the staff, and in a grand staff, its line is missing except for when needed for the note, middle C. 

All this happened between the Dark Ages and Renaissance. 

From the Renaissance to Baroque, music was written in only two keys; C and F. They are close. F has the note bB, while C has the note hB. If a composer wrote in a distant key, like E with four sharps, the mathematical relationships in perfect tuning in C didn't work. 

During the Baroque, composers messed around with tempered tuning, coaxing certain notes a little higher or lower, to make distant mathematical keys and relationships sound good and acceptable J.S Bach did this best, and published a work showing off how it was done on a harpsichord or clavichord. The work, Well Tempered Clavier, was a set of 24 preludes and fugure in the 12 major, and 12 minor keys. That set the standard for everybody. In that way, Bach influenced all music that came after him. 

Siagiah wrote:

**chuckle** 

It was fancier because Pikes is a professional composer who studied at Juilliard.

"Chuckle" 
Trish put it more direct and succinctly.