So Homo sapiens is correct in print, and Homo sapiens when writing by hand. Today the reconstruction of phylogeny is a very important aspect of systematics, at its very heart. The two major and complementary tools used in phylogenetic reconstruction are comparative morphology and comparative biochemistry. Comparative morphology is the study of structures. Comparative morphology includes the study of anatomy, the study of embryos, the study of cellular structure using microscopes, the study of fossils, and the study of behavior, which is a consequence of how the body and nervous system are structured.
Comparative biochemistry is the study of the arrangement of molecules in organisms.
Comparative biochemists may study the amino acid sequences in proteins, the nucleotide sequences in DNA and RNA, and may try to obtain DNA from fossils for comparison with living organisms. Both comparative morphology and comparative biochemistry can be used to study divergence and convergence, the two major types of evolutionary change. In divergence, organisms that share a common ancestor become more different with the passage of generations. In convergence, organisms that do not share a recent common ancestor become more similar. Divergence is much more common than convergence.