Early humans ate raw flesh as they didn't know how to cook their food. They had seen broken out fire in jungle severally, but didn't know how to make it and how they could use it..Sometime they felt that they could use it for keeping themselves warm in winter. But making fire was really a big problem and very hard. So, they decided to keep jungle fire burning and started to adding dry grass or leaves to it. But it was not a permanent solution.
One day, they saw sparks coming out from rubbing stones who were rolling down from the hills or some other way and got idea to make fire by rubbing two stones. This was really a great discovery as now they were able to make fire whenever required. With time, they learnt other uses of fire too. They found that they can light up their caves and protect their family from cold and wild animals using fire. They also came to know that the roasted food is much softer than raw one and also tastier to eat and this was the beginning of cooked food.