• Homologous structures are similar structures in related organisms. The most important thing to remember about homologous structures is that they share common ancestry.
• In other words, only organisms that are somehow related to each other can have homologous structures.
• For example, a chimpanzee’s arm and a human’s arm are homologous structures.
• Both sets of arms have a similar structure and use and chimpanzees and humans share a common ancestor.
Yes, it is necessary that they have a common ancestor, since otherwise there cannot be any similarity in basic plan, origin or internal structure.
