Wider hips may make childbirth easier, but increase the risk of other health issues
By Michael Le Page
10 April 2025
Pelvis width may influence the risk of birth complications and back pain
Cavan Images/Getty Images
The width of a person’s hips seems to be a result of complex trade-offs between the evolution of larger brains and upright walking, according to the largest study of its kind to date.
“If your brain is getting larger and larger over the same evolutionary time as your pelvis is getting narrower, this, of course, results in conflict,” says Vagheesh Narasimhan at the University of Texas at Austin.
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This idea, first proposed in the 1960s, is known as the obstetrical dilemma. More recently, it has been suggested that the risk of pelvic floor conditions also factors in. The pelvic floor is a layer of muscles that keeps our organs in place. If it weakens or tears, it can lead to incontinence and problems during childbirth.
“The obstetrical dilemma has been debated very hotly,” says Narasimhan. There have been many previous studies trying to relate the structure of the pelvis to walking speed and efficiency, for instance, but these studies have usually involved small numbers of people and produced conflicting results, he says.
Now, Narasimhan and his colleagues have used data from the UK Biobank to look at 31,000 men and women. The team measured various aspects of the pelvis based on a type of scan called dual-energy X-ray absorptiometry and looked for correlations with genetic variations and aspects of people’s health, such as requiring emergency caesarians.