i think there is something to this mass body temp decrease. i think its the industrial age and all the coal(fine hydrocarbons) dumped into the air. at least that was the beginning.
i really feel this is true, that normal human body temp is closer to 100 ((37.78 C). 99.5 sounds right. thats what you see in babies and i see no reason their temp would be an exception. they are fairly untainted humans.