Final answer:
Genetic similarities, supported by fossil records and physical characteristics, are primary indicators for determining evolutionary relationships between organisms. Homologous structures in particular, which reflect both morphological and genetic evidence, are vital in constructing accurate phylogenetic trees.
Step-by-step explanation:
Evolutionary relationships between groups of organisms are best determined using genetic similarities and fossil records. While physical characteristics, such as morphological information, have been used historically, genetic information provides a more accurate representation of phylogenetic relationships. Homologous structures are one example where both form and molecular evidence must be considered.
These homologous characteristics suggest a shared evolutionary history and help scientists build phylogenetic trees. However, it's essential to also consider the possibility of analogous traits which may look similar but have evolved independently. Modern technologies in molecular biology have proven invaluable in distinguishing these traits and confirming evolutionary hypotheses initially informed by physical and fossil evidence.
Modern phylogenetics leans on molecular data alongside the traditional morphological and fossil data to better understand and illustrate the evolutionary relationships, enhancing scientists' ability to map accurate phylogenetic trees.