The most likely reason for today's population growth in certain areas or countries is because of a combination of factors, including increased access to healthcare, improved living conditions and technology, and declining infant mortality rates. Additionally, some countries may have higher birth rates due to cultural or religious beliefs, as well as government policies that encourage or discourage population growth. Migration, both domestic and international also play a role in population growth or decline. In the case of China, it has had a one-child policy for several decades that may have contributed to its population growth.