<span>The difference between the number of live births and the number of deaths during the year. When the number of births exceed the number of deaths.</span><span />
When merchants traveled between towns selling goods, they would have items from different places and cultures. The buyers of these merchants would be fascinated with the new items they had never seen before of different cultures, and so they would buy those items and spread them around until everybody knew about and became interested in other cultures. The cycle continued, causing more and more people to appreciate other cultures.