why are theories such an important part of the understanding of human development?

Human development is a very complex subject and many ideas, although very different, can work as explanations. Because of this we must test different ideas, to see if they play out the same way as theorized. It is also possible that many different factors in different regions played in our development and the only way to confirm our history is to test theories to see if they are confirmed or disproven.

all you really need to do is work on the punctuation and substitute some words to make it shorter