What factors explain the rapid population growth of humans that has occurred since 1500?
Well, decrease in death rate and improvements in medicine...
As time passed on, more and more improvements were made in medicine. Some examples include more vaccines, more education in keeping safe from diseases, etc.
This led to less people dying from diseases.
Also, increase in fertility could be another factor, with less rates in mortality, which leads to more population growth.
Increase in average human age lead to more people living longer as well...