It was determined to be 98.6 Fahrenheit back in 1851:
Researchers say that the body temperature (Fahrenheit) of men born in the 2000s is on average 1.06 degrees lower than men born in the early 1800s. Similarly, women born in the 2000s have an average body temperature that is 0.58 degrees lower than women born in the 1890s. All in all, these conclusions point to a decrease of 0.05 degrees among the U.S. population each and every decade.
John Anderer, “Human Body Temperature In The U.S. Has Decreased Over Time, Study Finds” at StudyFinds
In all 677,423 temperature readings were taken, dating back to the US Civil War era. The open-access paper was published in eLIFE.
From the discussion: “Our investigation indicates that humans in high-income countries have changed physiologically over the last 200 birth years with a mean body temperature 1.6% lower than in the pre-industrial era. The role that this physiologic ‘evolution’ plays in human anthropometrics and longevity is unknown.”
If “evolution” is going on all the time like that, and probably drifting back and forth, what becomes of the Facts of Evolution that are the Bedrock of Science and the Truths every schoolchild should be taught?