Final answer:
The theory posits that the Indo-European languages evolved from Proto-Indo-European, spreading through ancient migration, trade, and conquest.
Step-by-step explanation:
One theory regarding the origins of the Indo-European language family suggests that Proto-Indo-European was the earliest known ancestor of a group of related languages and was probably spoken about 6,000 years ago.
As populations migrated, their language evolved and differentiated into the languages we recognize today, such as those within the Romance, Germanic, and Slavic subfamilies in Europe, as well as Indo-Iranian languages like Hindi and Farsi in Asia. The linguistic map points to ancient migration patterns, suggesting that these languages were spread by a combination of factors including trade, conquest, and cultural exchange.