Hip at what cost? How the human pelvis adapted to bipedalism and childbirth

Project Information

RISEN

Grant agreement ID: 101108385

DOI

10.3030/101108385

EC signature date 24 April 2023

Start date 1 March 2024

End date 28 February 2027

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 265 099,20

Coordinated by

ALMA MATER STUDIORUM - UNIVERSITA DI BOLOGNA
Italy

Periodic Reporting for period 1 - RISEN (Hip at what cost? How the human pelvis adapted to bipedalism and childbirth)

Reporting period: 2024-03-01 to 2026-02-28

Summary of the context and overall objectives of the project

When our ancestors began walking upright millions of years ago, the human pelvis underwent a dramatic transformation. This shift to bipedalism — walking on two legs — was one of the defining moments in human evolution, but it came at a cost. As the pelvis reshaped itself to support an upright posture, and as the human brain grew larger over time, giving birth became increasingly difficult. Today, complications during childbirth remain a major global health concern, contributing to maternal mortality and long-term conditions such as pelvic floor disorders.
Despite decades of research on how the pelvis differs between men and women, a fundamental question remains unanswered: how does the pelvis actually develop from birth to adulthood, and what factors — biological, environmental, and social — shape its final form? This gap in knowledge limits our ability to understand why some women face higher risks during delivery than others.
RISEN addresses this gap by studying pelvic development across the entire lifespan, from infancy to old age, using advanced three-dimensional imaging and shape analysis techniques. The project asks four key questions: How do the different parts of the pelvic bone grow and change together during childhood and adolescence? How do factors such as body weight, health, and living conditions affect pelvic shape? Are there specific bone features in women that can be linked to a higher risk of birth complications? And how does pelvic development in modern humans compare to that of our fossil ancestors?

RISEN combines evolutionary research with women's health to bridge this knowledge gap. By understanding how the pelvis develops and what influences its shape, the project aims to contribute new insights relevant to both human evolution and clinical practice.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first two years, the project built a comprehensive digital collection of three-dimensional pelvic bone scans spanning the entire human lifespan — from newborns to adults — drawn from skeletal collections from different sources and countries. All scans were processed to create detailed digital models of the bone surfaces, accompanied by a database recording each individual's biological and life-history information.
Using these digital models, the researcher analyses the morphology of the three parts of the pelvic bone — called ilium, ischium, and pubis — to study how they grow and change during childhood and adolescence. Results show that these three elements follow partly independent developmental paths, suggesting the pelvis works as a modular system rather than a single rigid structure. This modularity may be one of the mechanisms that allows the female pelvis to accommodate the competing demands of upright walking and childbirth.
A parallel line of research examined how pelvic morphology varies between sexes and across geographically diverse populations. The first project manuscript reporting these results has been submitted to an international peer-reviewed journal.
The internal microscopic structure of pelvic bones is also being analysed to understand how mechanical forces related to walking and posture are recorded in the skeleton. Additionally, the same methods are being applied to fossil specimens from extinct human species, to provide an evolutionary perspective on how the pelvis has changed over millions of years.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

RISEN advances current knowledge in several ways. Most existing studies on pelvic morphology focus on adults and treat the pelvis as a single anatomical unit. RISEN systematically studies the development of all three pelvic bone components — ilium, ischium, and pubis — separately and across the full growth period, from birth to adulthood. This approach has revealed that the pelvis is organized as a modular system, with each component following a partly independent developmental path. This finding challenges the traditional view of the pelvis as a fixed compromise between walking and childbirth, and suggests instead that its structure allows for a degree of flexibility in responding to different functional demands.
A second contribution lies in the combination of external bone morphology with the analysis of internal bone microstructure. By examining both the outer shape and the inner architecture of pelvic bones, RISEN provides a more complete picture of how the skeleton records the mechanical forces associated with locomotion and posture throughout life.
Finally, the application of these methods to fossil specimens of extinct human species offers new comparative data on how pelvic development has changed over the course of human evolution.
Looking ahead, the project's final year will focus on publishing the results obtained so far and on exploring the feasibility of a predictive model linking pelvic morphology to childbirth risk factors, using clinical data collected in collaboration with clinical partners.