Fig. 2From: Speciation and Bursts of EvolutionA phylogenetic tree, the filled circles are called nodes and represent an event of speciation in which—moving from left to right—one species becomes two. The horizontal branches measure the amount of genetic evolution between speciation events. The vertical lines have no meaning and are just for spacing. What we refer to as a ‘path’ (see text) is highlighted in red through the tree. The amount of evolution along a path (sum of the horizontal branches) is called the path length. The red circles identify the speciation events along that pathBack to article page