The bigWig files in this directory represent conservation scores as computed by the GERP software:
http://mendel.stanford.edu/SidowLab/downloads/gerp/
on Multiple Sequence Alignments (MSA) of whole-genomes

Information on the current set of Ensembl MSA and the species used to generate them can be found here:
http://www.ensembl.org/info/docs/compara/analyses.html

Each file lists the conservation scores of each position of the genome for which those could be
computed (a minimum number of species have to be aligned). Positive scores represent highly-conserved
positions while negative scores represent highly-variable positions.