Question: Why do we stand up straight?

Shane Mc Guinness answered on 13 Nov 2013:

Great question again Leah.
So, there are a few theories, like everything in science!
One is that we evolved the ability to stand upright as primitive apes so we could move much longer distances to find food. Also, this would help with escaping predators. This is probably because our ancestors came down out of the trees for some reason (where standing upright is pretty useless!) to moving around flatter fields called savannah in Africa. In order to find food here it’s more efficient to walk and the skill of climbing isn’t much use.
The other theory (and one which I prefer because it sounds really cool!) is that it evolved in apes who needed to wade through water to get food. It’s easier to walk through water, because you’re lighter. Then gradually their bodies changed over many generations to allow us to only walk upright. If you look at a skeleton of humans and compare it to a chimpanzee (our closest relative), it’s still very different so this change would have taken a very long time. One of the key changes was in the hip bones, or the “pelvis”. This had to tilt downwards so we could stand up straighter.
So, because we needed to find food in a habitat that was changing around us, either to less trees of more water, some of our ancestors began to walk on two feet. And because they survived and others did not, they passed these changes on to their children and so made this skill even better.