Complex sentence: Having evolved from viruses that infected animals, they emerged first appeared in humans in Europe and North Africa thousands of years ago, the viruses were later carried to the New World by Europeans during the time of the Spanish Conquests.
Split into simpler sentences: Having evolved from viruses that infected animals, they emerged first appeared in humans in Europe and North Africa thousands of years ago. The viruses were later carried to the New World by Europeans during the time of the Spanish Conquests.