, known to biologists these days as "
DNA or Non-coding DNA
makes up around 97%
of the human genome
These are sections of DNA which don't code for protein
However, not all Non-coding DNA has to be actually worthless to the cell.
There are numerous functions that have been found in this "junk". For
example, there is strong evidence that in Cryptomonads, the amount of
non-coding DNA is proportional to the size of the nucleus. The same
study also indicated that natural selection is able to weed out true
junk DNA (1).
Information grabbed from the much more thorough http://godandscience.org/evolution/junkdna.html
(1) Beaton, M.J. and T.
Cavalier-Smith. 1999. Eukaryotic non-coding DNA is functional. Proc. R. Soc. Lond. B. 266:2053-2059.