The best response to the question about the spread of the potato and its relationship to an increase in population in the Old World is:
The potato grows easily in cold, harsh climates. This means that it grew well in places like northern Europe, leading to an increase in population.
Potatoes are remarkably adaptable and can thrive in a variety of climates, particularly in regions with cooler temperatures. This ability to grow in less hospitable environments contributed significantly to food security in Europe, allowing populations to increase as a result of improved nutrition and food availability.