(i) Reproductive isolation is the prevention of interbreeding between the populations of two different species, whether they are geographically isolated or living close together. Some in built (genetic) mechanisms prevent them from interbreeding and producing fertile offsprings.

(ii) Homologous organs are those which have a common origin and are built on the same fundamental pattern, but they may have similar or different appearance due to similar or varied functions. Homology is exhibited by every organ system of vertebrates from lowest to highest including man.