Simplify the following text for a Grade 7 native English-speaking person.
Original: By about 5500 BC , small tribes living in the Nile valley had developed into a series of cultures demonstrating firm control of agriculture and animal husbandry , and identifiable by their pottery and personal items , such as combs , bracelets , and beads .
Simplified: By about 5500 BC , small tribes living in the Nile valley had developed into a series of cultures .