Let's just make a general blanket statement that we pretty much all know to be true: people love butts. Butts of all shapes and all sizes - we love them all.
But, you know you've asked the question before. Why do we have butts?
Let's break it down:
Our butts are the biggest muscle in our bodies. In humans, the shape of the butt is fairly unique to the species. Think about it - what other animal out there really has a butt that's going to look so good in leggings?
Part of the reason that we have butts at all relates to that very fact. Humans, unlike our four-legged friends, walk upright. As opposed to quadrupedal apes, human torsos rest on top of the legs. That means hi muscles and the gluteus maximus need to be positioned more toward the backside of the pelvis - thus, making your butt look like a butt.
Strong butt muscles, then, help us in a very important daily activity: walking, and keeping your torso upright. Yep, if it wasn't for your butt, you couldn't even stand up correctly. Butts keep us balanced while walking and running.
Because humans are bipedal as well, it means we also tend to sit upright, another fairly unique trait of the human species. Imagine sitting down on your butt if you didn't have muscles or fat. Yep, that wouldn't be so comfortable, would it? Butts are literally built in padding for when you're at rest.
People with back pain might want to look to their butt for an explanation. That's a sentence you thought you might never read, isn't it? If you have a stronger butt, it might aid in your back pain - because we now know that our butts are the things responsible for helping us stand, so if we have weak butt muscles, our standing and sitting habits might be bad.
So, we know why we have butt muscles, but why are our butts big?
One possible reason is a little extra padding around the hips, thighs, and butt is a good way to store fat. In a hunter-gatherer society, humans often faced food shortages, and potentially adapted to storing fat around those areas.
And, last but not least, a study in 2008 said that women with bigger hips and butts performed better on average on tests than women with small hips and butts. They posited a large hip-waist ratio supports neurodevelopment, potentially because the hip and butt area store omega-3 fatty acids, which support brain development. Yay for butts!
Oh, we also have butts so we can wear Cute Booty. Never forget that fact.