Why is my body temperature 37 degree Celsius ?

The  evolution of  'warm-bloodedness' lies at the
 heart of this question.

Our bodies are product of thousands of natural selection which started from the origin of life. We are handed down relics of ancient beings, their manifestations which allowed them to survive. One of the fascination question is to ask why did nature select present body temperature ? Where did it all originated ? 

One of the reason as pointed by Crompton et al. could be the need to forage at relatively variable temperatures of the environment. Reptiles, which were predominantly active during the days had to rest during the night. This created the vacant niche and that consequently selected for nocturnal mammals. Those first mammals which had higher metabolic rate and insulation were better adapted to forage at nights.
 The fossil evidence suggests that first mammals had five-fold higher increase in brain size. This suggests that senses of smell and hearing, compensated for the vision in these nocturnal environments.