How incomplete is the fossil record?
Systematic biologists cultivate a unique orchard. Following in the footsteps of Charles Darwin, they grow phylogenetic trees — branching diagrams that depict lines of evolutionary descent back to a common ancestor. Also known as phylogenies, these assemblies of lines and classifications chart biodiversity with varying specificity, from individual organisms to broader taxonomic rankings such as kingdoms and domains. With each tree, these biologists come closer to uncovering something even greater: a four-dimensional model of life itself. Scientists use a number of tools to reconstruct the tree of life. They depend heavily on cladistics, a method of hypothesizing relationships among organisms. Think of it as creating a family tree with blank spaces for unknown ancestors. They also turn to molecular sequenci
