Our buttocks are unique among all creatures, even compared to apes and gorillas. The shape of our buttocks is unique to the human species. So why is this the case? That's because of the main muscle in our buttocks: the gluteus maximus.
The shape of our buttocks began when we went from quadruped apes to biped apes hundreds of millions of years ago. Because humans walk upright, we alternate between two legs and one leg, and most of the time we walk with one leg supporting our entire body, a lot of the muscles in our ass have changed in order to support our entire torso.
Our ass are made up of the gluteus minimus, gluteus medius and gluteus maximus. Of the three types of gluteus, the gluteus maximus forms the iconic shape of the human buttocks. The gluteus maximus arises from the upper iliac crest and passes down to the coccyx. The gluteus maximus attaches to the top of the femur and is the main extensor in our thighs. When we make big motion changes, or need to move our thighs quickly, we use the power of our gluteus maximus. It is our primary source of motivation when we run, climb stairs, and stand up from a sitting position. This is why sprinters and weight lifters tend to have rounder, firmer hips.
In addition, we have a lot of fat on our buttocks, which helps us cushion ourselves when we walk or sit down and avoid injury, which is part of what makes our buttocks so plump. https://www.meiwoanatomy.com/