Which organism can change its sex?

$A$ zygote which has an $X-$ chromosome inherited from the father will develop into a

What evidences can suggest that, "Modern human beings have originated in Africa"?

What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.

"The chromosome number of the sexually reproducing parents and their offspring is the same." Justify this statement.

What are the organs called that perform different functions but have a similar basic structure?