Fig. 10

There are no “main lines” or “side tracks” in evolution. Undoubtedly, many readers will consider the tree depicted in a to reflect a main line of evolutionary progress from a primitive ancestor to an “advanced” species like humans, with other groups such as cartilaginous or bony fishes appearing as side tracks off that line, despite the fact that roughly half of all vertebrate species are teleost fishes (and only 10% are mammals). Notably, the tree in b is equally valid and by the same false logic would have perch as the endpoint of an assumed main line and all terrestrial vertebrates, including humans, as an apparent side track. It is important that the positions of terminal nodes, all of which represent contemporary species, not be mistaken as having some significance, because they do not (see also Fig. 11). Note also that humans are more closely related to bony fishes than either is to sharks. Phylogenetically speaking, “fish” is an invalid category resulting from different rates of morphological change among lineages and does not reflect real relationships