Human beings first developed the ability to stand on two legs following two critical evolutionary changes to the ilium in the upper part of the pelvis.

This finding is reported today in top journal Nature by an international team including Niamh Nowlan, Professor of Biomedical Engineering, UCD and a Fellow of the Conway Institute on the Belfield campus.

The ilium is the big, flared part of the pelvis that anchors the powerful gluteus maximus muscles that humans use to stay upright. Differences in the illum between humans and other apes are a defining evolutionary difference.

“The most important impact of the paper is that it shows us how changes to the formation of the ilium contributed to bipedal gait in humans,” said Prof Nowlan, who began this research after meeting Dr Terence Capellini, a Harvard University anthropologist, at a scientific meeting.

“In this paper, the evolutionary shift in morphology of the pelvis that enabled bipedal locomotion has been revealed, largely through looking at the embryo,” said Prof Nowlan.

Dr Capellini, who led the research, studies the evolutionary origins of bipedalism, while Prof Nowlan is interested in the human hip before birth.

Alongside Professor Owen Arthurs, a paediatric radiologist from Great Ormond Street Hospital and University College London Hospitals (UCLH), Prof Nowlan, in previous work assembled a dataset of 3D imaging data from human embryos and foetuses to characterise hip development.

This data, which she shared with Dr Capellini, revealed that the ilium, develops differently in humans in two ways that are different from other primates.

One change involved the direction of cartilage growth, said Prof Nowlan, with a shift in the orientation of the cartilage growth plate, the physis, enabling the ilium to sit perpendicular to the direction seen in ilia from other animals.

The other involved the process of bone formation, with the scientists identifying differences in the way that bone cells are laid down over the cartilage in the human ilium, compared with non-human primates.

“It’s these two key changes in the ilium’s angle and mineralisation that were crucial for humans to stand and walk on two legs while still accommodating a large birth canal for big brained babies,” said Prof Nowlan.

“This study reveals the evolutionary shift in morphology of the pelvis that enabled bipedal locomotion, largely through looking at the embryo. Prenatal development of the skeleton is a fascinating subject and there is still so much to learn.”

Prof Nowlan’s work has significant medical implications for hip dysplasia, a condition where the hip joint doesn’t form properly, can lead to pain and mobility issues from infancy into adulthood.

Using MRI and CT scans, her team tracks skeletal development and prenatal movements to better understand how mechanical forces influence joint formation and stability.

“I had hip dysplasia myself as a baby and later severe hip problems requiring surgery,” said Prof Nowlan – a personal connection that fuels her passion for getting better diagnostic and treatment methods for the condition.

Published in the Irish Indepedent, 28/08/25