Phylogenetic systematics, a.k.a. evolutionary trees :
Using trees to learn about the evolution of complex features: The striped cichlid
Reconstructing ancestral characters can help us understand how a complex feature evolved. For example, the cichlid fish shown above and represented below vary in shape, color, and striping patterns.
Researchers reconstructed the phylogeny of these fish based on molecular data, then mapped striping patterns onto the phylogeny. Scientists used parsimony to infer the probable pattern of the ancestral fish. The resulting phylogeny shows how these complex patterns evolved in different lineages.
This technique helped biologists figure out that evolutionary changes in cichlid striping pattern seemed to be related to ecological shifts not sexual selection. Similar techniques have been used to understand, for example, how birds evolved the ability to fly and how tetrapods evolved to live on land.