Roman Diversity: 1) Etruscan contributions include the arch, writing, language elements, sewer system, city planning, religion, art, metal work.  2) Greek contributions include philosophy, education, architecture, religion, culture, military technology, colonization.  3) Egyptian contributions include medicine, religion, construction techniques, agricultural methods, government organization.  4) Jewish contributions include religion.  5) Phoenicians (Carthage incl.) ship technology, trade, phoenetic alphabet.  

I hope this list which could easily be added to is illustrative of how a diverse society promotes innovation and progress.