How can we tell that two species shared a common ancestor

Explanation:

Homologous structures provide evidence for common ancestry, while analogous structures show that similar selective pressures can produce similar adaptations (beneficial features). Similarities and differences among biological molecules (e.g., in the DNA sequence of genes) can be used to determine species' relatedness.

Two species are more related if they have a more recent common ancestor, and less related if they have a less recent common ancestor.

because they can.

Explanation:

srry but ure not specific

energy and particles