When and why our ancestors began to wear clothing is a curious story.
Clothing may have emerged for insulation of body heat. Similarly it also have provided a means to carry things and improve mobility. Cold snaps engulfed the earth many times. Using ice cores from Antarctica scientists identified 8 glacial cycles within the last 800 thousand years alone. An archaelogical site from Israel provides the earliest evidence of controlled fire by humans spanning the same time period.
We know very little about our universal habit. One very strong clue comes from human head lice and clothing lice. Lice living in clothes evolved from the head lice sometime between 83 thousand to 170 thousand years ago. Based on the molecular clock of the Melanocortin 1 receptor, scientists calculate that humans started to loose body hair starting from 1.2 million years ago.
You can follow sequences of important geological and evolutionary events in this timeline.