What are some aspects of a species' evolution that can't be studied using fossil evidence? why don't fossils provide information about these characteristics?

Fossils records provide evidence about the history of life on Earth including how organisms have changed over time. It tells about the structures of ancient organisms, their environment, and the way they lived. However, fossils can not usually provide information about soft tissues of an organism because soft tissues rarely become fossilized. Additionally, fossils rarely provide information about interactions among organisms and therefore tell us little about animal behavior. 

Control variable- changedependant variable- stays the samechanging- food itemsdependant- presences of proteins