The human body has an average temperature of about 37 °C/98.6 °F.
Why that temperature in particular? Why not, say, 14 °C or 50 °C?
Is there something magic about, say, the speed of reaction of certain enzyme-catalysed processes at that temperature that makes this body temperature particularly desirably? Or is it, say, an attempt to be above average ambient temperature (since it's easier to create heat than to cool down) while not being too much above it (which would require more energy expenditure)?
Is it an arbitrary constant?
Inquiring minds want to know!