As adults, we remember best recent past than what was 10 years ago. We remember better events that had a big influence on us. The same thing is with world history and the past. We don't remember things when we were a baby, but they use to tell us how it was, even before you were born. Well some people don't know their early past, some people don't have parents, some people never heard their parents speaking about that, some are adopted, some even don't know it. Just compare one person's history with the world's history. What do all people in the world have in common? Diversity.