OK, you keep your bum! This does mean it costs more muscle energy to digest food as it has to move against gravity, but your gut is longer, so perhaps you get more out of it. But it's definitely good enough.
In fact, if you are going to push food right through you, it might make sense to make the gut bigger and bigger so that it can extract as much energy and nutrients as possible from your food.
Should my bum look big?
Yes
No
Evolution starts with the Last Universal Ancestor.
You can find out what happened before evolution here.
You can also short-cut to Land plants, or Animals
