Here is the completed text with the past simple form of the verbs in brackets:
The human story
The first humans!
They hunted animals and gathered nuts for their food. They looked for fruit, seeds and traveled from place to place and carried their young children with them. Big families weren't possible. But about 10,000 years ago, humans invented farming, probably in the Middle East, and human life changed completely. The first farmer planted some seeds in the earth. "You are wasting your food," his tribe waited. Soon he laughed. But the farmer noticed little green plants in the earth and these produced a lot of food. The people in his tribe chatted to other tribes, and they copied the farmer's idea. Soon there were a lot of farmers, and humans stopped traveling. They lived in small villages, and could have more children because they weren't traveling all the time. The human population started to grow.