Which group of countries has higher populations?

• In 1950, the total global population (top of the bar) is approximately 2.5 billion.
• The population of "Less Developed Countries" (bottom, lighter part of the bar) is approximately 1.7 billion.
• The population of "More Developed Countries" is the difference between the total population and the population of "Less Developed Countries".
• Population of More Developed Countries in 1950 $\approx 2.5 \text{ billion} - 1.7 \text{ billion} = 0.8 \text{ billion}$.

• $0.8 \text{ billion} = 0.8 \times 1,000,000,000 = 800,000,000$ people.

• 800,000,000 is significantly greater than 1,000,000.

Since the population in "More Developed Countries" was already approximately 800 million (or 0.8 billion) in 1950, it must have risen above 1 million at some point before 1950.

Therefore, the correct option is A.

The final answer is $\boxed{\text{A. before 1950}}$