Why Early Humans Began to Walk on Two Feet

 Why did early humans begin to walk on two feet?
    Explore all the possible reasons and give concrete examples to support your thinking.
One possible theory is that about 5 million years ago, Africa was covered in forests, but then the forests started getting smaller, and where the forests used to be, there was grassland. The early humans needed to go through the grasslands to get to the forests, but the grass in the grassland was very tall, so they had to stand upright to over the grass to see where they were going. A very similar and closely linked theory is that the humans lived in the forest, but they had to leave the forest to get food, and when the food started to get further and further away, the humans had to walk longer distances, and they walked upright because it was more efficient and they didn't waste as much energy while walking the long distance to get to the food. As time went on and the humans developed more, the early humans developed longer legs that let them get further in each step with the same amount of energy. A different theory about food is that the humans had to stand upright to reach fruits on higher trees. While bent over, you cannot reach as high, so you can only reach lower fruits, ut while upright you can reach higher fruits.An additional theory related to food is that when a male had am mate and made her pregnant, he had to hunt for extra food for the baby, and walking upright allowed the male to carry more food, wood or other supplies for the whole family in his arms. This works because if he is walking on all fours, none of his hands are free for carrying, but if he is walking on 2 feet,, his arms can be used for carrying. A completely unrelated theory is that the early male humans stood upright to help attract a mate, or to show that he is more powerful/dominant than some other male. In other words, standing upright could be a show of force. This could be true because modern chimps also stand up when they are trying to show force. In all of these theories, the walking probably occurred only part time, though. For example in Lucy, the 3 million year old Australopithecus Afarensis, she had Long legs and a toes that were suited for walking. However, she also arms suited for climbing and swinging in trees.