Why did early humans begin to walk on two feet?

Early humans began walking on two feet because they needed 2 hands in order for them to use tools. Before they walked on two feet they couldn't use their hand effectively as they do on two feet. Early humans also could have walked on two feet because they wanted to impress the opposite gender by gathering the most food. For the early humans the one who has the most food was the most popular. Another reason could have been that they needed a faster way of walking and they found walking on two feet faster.