Evolutionary space. Every core gene of Campylobacter is represented as a dot in the space spanned by the three first principal components in our analysis. Instead of a three-dimensional plot we have used three pairwise scatter-plots, the upper panel being the most important (component 1 and 2). Explained variance is a measure of importance of the components, and is given by percentages of the total on each axis. The seven MLST-genes as well as the marker PorA are indicated in the upper panel only. Genes that are close to each other in this space show similar values for the 351 normalized pairwise evolutionary distances. Partitioning the CGFs into K=5 clusters leaves us with the clustering shown by the coloring of the dots. The blue and the cyan groups are both making up the central group of the CGFs, containing 935 of the 1180 Campylobacter core gene families. The red cluster, containing 120 CGFs, is separated from the blue along PC1. The green group (103 CGFs) is separated along PC2 and the scattered brown group (22 CGFs) mainly along PC3.