* Breeding Behavior: While reproductive isolation is a key factor in speciation (the formation of new species), it's not always the primary way scientists determine evolutionary relationships. It's more useful for understanding how species diverge within a lineage.

* Geological Distribution: Geographic isolation and biogeography play a crucial role in evolution. Scientists use the distribution of species across different locations to understand how they may have evolved and spread. This is a strong piece of evidence.

* Structural Similarities: This is a major factor in determining evolutionary relationships. Scientists look at homologous structures (structures with similar underlying anatomy, even if they have different functions) to infer common ancestry.

What's missing?

The most powerful tool scientists use to understand evolutionary relationships is molecular data, specifically DNA and RNA sequences. These molecules change gradually over time, and by comparing these sequences across species, scientists can reconstruct evolutionary trees with remarkable accuracy.

Therefore, while breeding behavior, geological distribution, and structural similarities are important factors, molecular data provides the most comprehensive and reliable picture of evolutionary relationships.