Final answer:
At the beginning of the 21st century, Asia had the highest population, attributable to the massive populations of China and India.
Step-by-step explanation:
The region of the world that had the highest population at the beginning of the 21st century is Asia. By 2010, the global population growth was about 80 million people per year, largely driven by increased populations in developing countries, particularly on the continent of Asia. Additionally, China and India, both part of the Asian continent, are recognized as the world's most populous countries, with populations exceeding one billion individuals each. Moreover, while the continent of Africa has the highest fertility rates, its population numbers are still less than those found in Asia.