The feeling of “not having hips” often stems from the difference between a desired visual curve and the underlying biological structure. When people refer to “hips,” they mean the outward, rounded contour of the lower body, which is a combination of bone, fat, and muscle. This visual appearance is distinct from the pelvis, the anatomical basin that connects the spine to the legs. Understanding this distinction is the first step toward understanding why hip shape varies so widely among individuals.
The Skeletal Foundation of Hip Shape
The underlying skeleton, specifically the pelvis and upper thigh bones, determines hip width. Pelvic width is measured primarily by the distance between the iliac crests, the flared edges of the hip bones felt just below the waist. A wider distance here sets a broader base for the hip structure.
Another important skeletal measurement is the distance between the greater trochanters, the bony knobs on the upper part of the femur (thigh bone) that project outward. These trochanters are the widest bony points of the hip region and directly influence the lower body contour. The ratio between the width of the iliac crests and the greater trochanters significantly determines hip shape.
While biological sex provides a general tendency for pelvic shape, wide variation exists among all individuals. The female pelvis is often described as broader and shallower to facilitate childbirth, but this is a general trend, not a guarantee of wider hips. The angle of the femur where it meets the pelvis also affects how much the greater trochanters project, contributing to the visual appearance of hip width. Since bone structure is fixed after development, this factor is the least modifiable element of hip shape.
How Hormones Dictate Fat Distribution
Beyond the skeleton, the distribution of subcutaneous fat, regulated by sex hormones, influences hip shape. Estrogen is the primary hormone that drives fat accumulation to the gluteofemoral region—the hips, thighs, and buttocks—during puberty. This process creates the “gynoid” or “pear/hourglass” shape, typical of reproductive-aged individuals.
The timing and concentration of estrogen during adolescence permanently influence where adipose tissue is stored. Estrogens bind to receptors in the adipose tissue, stimulating lipid accumulation in the gluteofemoral depot rather than the abdominal area. If fat cells in the hip region are less sensitive to estrogen, or if the hormonal profile favors other storage areas, the characteristic hip curve may not develop, even in thin individuals.
Conversely, an “android” or “apple” pattern of fat storage, where fat is preferentially stored in the abdomen, is associated with lower estrogen or higher androgen levels (like testosterone). This difference in hormone-driven fat storage explains why some people retain a straighter shape regardless of body weight. The body’s ability to distribute fat is largely determined by this hormonal activity during developmental periods, with genetics dictating the sensitivity of fat cells to these hormones.
The Impact of Muscle Mass and Posture
While bone and fat are the major biological determinants, muscle mass and posture significantly influence the visual presentation of the hips. The gluteal muscles, particularly the gluteus maximus and gluteus medius, make up a large portion of the hip and buttock prominence. Developing these muscles through targeted exercise can add volume and contour, enhancing the outward curve.
The gluteus maximus is the main hip extensor, forming the bulk of the buttocks. The gluteus medius, located on the side of the hip, contributes to overall width and helps stabilize the pelvis during movement. Even with a narrow underlying bone structure, well-developed gluteal muscles can create a rounder, more pronounced hip silhouette.
Posture also plays a noticeable role in hip appearance, specifically through the angle of the pelvic tilt. An excessive anterior pelvic tilt, where the pelvis is tipped forward, can visually flatten the buttocks and make the hips appear less curved. Conversely, a neutral or slightly posterior tilt can enhance the hip curve and the projection of the glutes. The strength and balance of the core and gluteal muscles primarily maintain this pelvic positioning.
Genetic Inheritance and Body Type Variation
The combination of skeletal width, hormonal sensitivity, and fat storage patterns is largely inherited; genetics sets the blueprint for an individual’s body shape. Studies on twins and families estimate that the heritability of body fat distribution patterns is high. Biological inheritance accounts for a substantial portion of how the body distributes fat, independent of overall weight.
Scientists have identified numerous genetic variants associated with body fat distribution, suggesting that the precise location of fat storage is a complex trait influenced by many genes. This genetic background helps explain why two people with the same lifestyle and diet can have distinctly different body shapes. The concept of body types—such as ectomorph, mesomorph, and endomorph—reflects these inherited differences in bone structure and metabolic tendencies.
Ultimately, whether an individual has a pronounced hip curve or a straighter silhouette results from a specific genetic combination. This variation is a normal part of human biology. Understanding that one’s body shape is mostly predetermined by fixed factors like bone structure and programmed hormonal responses helps normalize this wide spectrum of natural human variation.