Final answer:
The most recently developed method to establish phylogenetic relationships is comparing molecular features like gene and amino acid sequences.
Step-by-step explanation:
The method among the listed options that has been developed most recently for establishing phylogenetic relationships among organisms is comparing molecular features, such as gene sequences and amino acid sequences.
This approach, informed by the advancements in molecular biology over the last fifty years, allows scientists to compare organisms based on genetic evidence, offering a more precise reflection of evolutionary lineage than previous methods.
Molecular comparisons have significantly changed the phylogenetic trees of many species, as genetic and molecular analyses provide insight that could not be inferred from morphology or the fossil record alone.