I was only 7 years old at the time, I really can't remember.

When fire was invented they realized their food tasted better and was abit easier to chew cooked than raw. They also didn't die as often of disease when they started cooking it I would assume.

As soon as fire was invented / discovered

The oldest generally-accepted evidence for controlled use of fire by humans dates to around 700,000-800,000 years ago and is from the site of Gesher Benot Yaacov in Israel. There are claims for earlier use of fire dating back to 1.4-1.8 Million years ago from sites in East and South Africa, but these are somewhat less convincing, -isolated burnt bones or burnt sediment patches that could just as well be results of natural fires. Current thought on the main evolutionary benefits of cooking plant foods is that exposure to heat can break up toxins (many of which have long molecular chains) that make some foods difficult for humans to digest. Cooking can also make hard foods softer (e.g., tubers), allowing for easier chewing and digestion. Cooking meat also kills bacteria and parasites. Among paleoanthropologists, the most popular theory about the origin of cooking is that it was linked to selective pressure for enlarged brains among younger hominins. The brain is an expensive tissue and increasing the quantitiy and quality foods available to juveniles may have enabled those among them with a genetic propensity to encephalization (developing large brains) to realize their potential. Undoubtedly it was more complicated than this, but that is the short version. Fire is also useful in keeping potential predators at bay, particularly at night, and it is conceivable that early hominins started messing around with fire for defense long before it ever occurred to them to cook anything. http://en.allexperts.com/q/Anthropology-2291/cook-food.htm http://www.beyondveg.com/tu-j-l/raw-cooked/raw-cooked-3a.shtml