What are vestigial organs?

Theory of chemical evolution states that organisms have evolved from inorganic substances. If so, what was the atmospheric condition that favoured evolution?

Name the connecting link for the following groups of organisms.
(a) Annelida and Arthropoda
(b) Reptiles and Aves
(c) Pisces and Amphibians
(d) Reptiles and Mammals

Why are analogous structures a result of convergent evolution?

Give the salient features of Mutation Theory.