I've been attending a meeting on obesity and diabetes this week (which explains the paucity of entries). A whimsical thought came to my mind as I listened to one of the many talks related to gene expression - the number of unique human beings is finite. Our genome is about 3 billion base pairs long. However, individuals differ in something like 3 million of these bases in what are called Single Nucleotide Polymorphisms (SNPs). Thus there are at most 4 to the power of 3 million unique individuals! Since two of every three SNPs, involves replacing cytosine (C) with thymine (T), this number is reduced somewhat. This is a very big number but it is still finite.
A much smaller number is the number of different pop songs. In most cases, pop songs consist of no more than 4 or 5 melodic phrases of 5 to 10 notes. George Harrison was sued for plagarizing his song "My Sweet Lord" for repeating 8 notes of the song "He's So Fine". Usually a song is identified by its ``hook'', which is a single melodic phrase such as "We All Live in a Yellow Submarine" or "My Sweet Lord ". Almost all pop songs are based on a diatonic scale in a minor or major key which consists of 7 notes. Pop songs are almost always in 4/4 time. In order to be singable, notes cannot differ too much in time or range. So let's say each note can be either a whole note, half note, quarter note or eighth note and in one octave. That gives 28 possibilities per note. For a 10 note phrase this is 28^10 different hooks, not an astronomically large number. However, a hook is usually identified by fewer than 10 notes and the timing of the notes can vary by a certain degree and still seem the same to most people. The rules of harmony also restrict transitions to a smaller set of notes. So maybe there are just 10 possibilities per note and since absolute key and tempo doesn't matter the first note is fixed. For a five note hook, there may only be 10^4 different combinations. In other words, there are only about ten thousand different possible pop songs! No wonder they are starting to sound the same to me.