Final answer:
Modern classification in biology is based on phylogeny, the evolutionary history, and relationships among organisms. It leverages genetic and molecular data in addition to morphological and fossil evidence to construct more accurate phylogenetic trees, which are subject to change with discoveries.
Step-by-step explanation:
Modern classification is based on phylogeny, which is the evolutionary history of a group of related organisms and their relationships to one another. Carolus Linnaeus initially based classification on physical similarities and differences, a practice that was limited to morphological observations. As scientific understanding advanced, particularly with the introduction of Darwin's theory of evolution, the importance of phylogenetic relationships became paramount. The use of DNA and RNA analyses has substantially changed and continues to change the evolutionary tree of life, indicating a greater reliance on genetic and molecular analyses in addition to morphology and fossils for building phylogenetic trees. In systematics, scientists utilize data from various sources, such as morphological characteristics, genetic evidence, and the fossil record, to assemble the phylogeny of an organism. As a result, phylogenetic trees may alter as new information becomes available, and they remain essential hypotheses of evolutionary relationships.