Final answer:
The Indo-European and Sino-Tibetan language families together are spoken by over 66% of the world's population.
Step-by-step explanation:
The two language families spoken by over 66% of the world's population are the Indo-European language family and the Sino-Tibetan language family.
The Indo-European family includes languages such as English, Spanish, Hindi, and Persian. It is spoken by about 3.5 billion people, which accounts for approximately 46% of the global population.
The Sino-Tibetan family includes languages like Mandarin, which is spoken by around 70% of the population. It has about 1.3 billion speakers, making it the most widely spoken language in the world.