Final answer:
Scientists can determine shared ancestry through genetic analysis, comparing DNA sequences, using molecular data, and applying cladistics and maximum parsimony to construct phylogenetic trees.
Step-by-step explanation:
Aside from finding homologous structures, scientists can determine shared ancestry among organisms by analyzing their genetic information. Genetic similarities can provide compelling evidence of a common evolutionary background.
By comparing DNA sequences, scientists can identify specific genes that are conserved across different species, which suggests that these organisms share a common ancestor. This method is complemented by molecular data, such as the presence of similar proteins or genetic markers that are passed down through generations.
Additionally, scientists use cladistics, which involves constructing phylogenetic trees based on shared traits to understand evolutionary relationships.
Finally, the principle of maximum parsimony is used to deduce the simplest explanation for the evolutionary history of organisms, based on the least number of major divergences from the evidence at hand.