The average body temperature of humans is not decreasing or increasing significantly over time. The standard normal range for human body temperature is typically considered to be 97.7°F (36.5°C) to 99.5°F (37.5°C). However, studies have suggested that the average body temperature may have decreased slightly over the past century, from 98.6°F (37°C) to about 97.9°F (36.6°C), but the reason for this is not entirely clear and it is still within the normal range of human body temperature. Some factors that may contribute to this include changes in the way temperature is measured, improved healthcare, and changes in the population's age and body composition.