Did you know that the average body temperature has been steadily dropping since the early 1800s? It has:
In 1800 the average body temperature was about 99°F. Today it's about 98°F. How about that?
And why has body temp declined? Basically, better health:
Change in the population-level of inflammation seems the most plausible explanation for the observed decrease in temperature over time. Economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age together are likely to have decreased chronic inflammation since the 19th century.
The planet heats up. Our (humans) temperature goes down. A was to compensate?
Unfortunately, even if the magnitude were the same, the effect is the opposite (if there would be one - there's no reason to think the human body's natural equilibrium temperature has changed at all in the past thousand years). A cooler natural body temperature means that it's harder for the body to cool down to the temperature it wants to be at. If our equilibrium body temperature were rising, it would mean that deaths from heat would be attenuated.
I recommend following the link and reading the paper. I've never seen something like that which includes requests by the review team for changes and the authors' response. In the comments, one person notes that "the impact seems to be twice as large between 1971 and 2007 than between 1860 and 1971.", but the proposed causative elements (level of infection, ambient temperature [HVAC]) should result in greater change between data set 1 and 2 than between 2 and 3.
A real treat to read.
I wonder, possibly, if this change is really just a measurement issue.
How accurate were the tools used in the 1800's? Heck, how accurate were the measurement tools in the early 1900's?
From the study::
One possible reason for the lower temperature estimates today than in the past is the difference in thermometers or methods of obtaining temperature. To minimize these biases, we examined changes in body temperature by birth decade within each cohort under the assumption that the method of thermometry would not be biased on birth year. Within the UAVCW [earliest data set], we observed a significant birth cohort effect, with temperatures in earlier birth decades consistently higher than those in later cohorts ...
Strikes me as thin support for accuracy over the decades, but maybe it's enough.
Perhaps it's all the plastic absorbed in our bodies that is keeping us cool.
We get enough plastic onboard and we'll last forever. Not actually looking forward to that.
Improvements in sanitation between 1800 and 1850 were probably not that great, but there would have been increase in vaccinations.
I'd also suggest that, as most of this data was probably collected in regions with winter, there may have been improvements in general construction that made the indoors less like the outdoors.
A reminder: the superfluous precision of 98.6º F is due to the actual standard being a nice round 37º C.
Another body aspect that has changed substantially (since agriculture, but even over the last 1000 years) is the jaw.
Compared to medieval skeletons, you can clearly see how wimpy our jaws are.
I suspect (though have certainly not done a study!) that something like this in part accounts for why (warning, non-PC comment ahead!) people in photos from say 1840s seem to be so much uglier than today, they look wrong in a way that's hard to pin down. Perhaps we can sense that their jaws look different from what we expect, though can't exactly explain why?
If you want to read more, you can start with
https://en.wikipedia.org/wiki/Human_jaw_shrinkage
Sure, just ask your dentist (or orthodontist) about wisdom teeth, and why most people's mouths are too small for them.
If declining body temperature is a measure of "economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age," the chart suggests that Black people are (as of 2000) on average better-off than White people.
Clearly, we're just cooler than we used to be.