Study on Heart Architecture Offers New Understanding of Human Evolution

An In-Depth Analysis of the Evolutionary Differences Between Human and Great Ape Hearts

An international research team from Swansea University and UBC Okanagan (UBCO) has made a groundbreaking discovery in human evolution by comparing the structural and functional differences between human hearts and those of other great apes. This study, published in Communications Biology¹, sheds light on the evolutionary adaptations that have enabled humans to develop larger brains and the ability to walk and run long distances.

The Comparative Study: Human Hearts vs. Great Ape Hearts

Exploring the Evolutionary Puzzle

Despite sharing a common ancestor, humans and non-human great apes have diverged significantly in terms of physical and cognitive abilities. Humans have evolved larger brains and bipedal locomotion, adaptations likely driven by the demands of hunting and long-distance travel. This new study provides another crucial piece of the evolutionary puzzle by examining the differences in heart structure and function.

Methodology: Echocardiography and Speckle-Tracking

The research team conducted a comparative study involving humans and our closest evolutionary relatives, including chimpanzees, orangutans, gorillas, and bonobos. These great apes, cared for at wildlife sanctuaries in Africa and zoos throughout Europe, underwent routine veterinary procedures during which the team used echocardiography—a cardiac ultrasound technique—to produce images of the left ventricle, the heart chamber responsible for pumping blood throughout the body.

Key Findings: Trabeculations and Cardiac Function

Trabeculations: The Mesh-Like Network

Within the left ventricle of non-human great apes, researchers observed bundles of muscle extending into the chamber, known as trabeculations. Bryony Curry, a Ph.D. student in the School of Health and Exercise Sciences at UBCO, explained,

"The left ventricle of a healthy human is relatively smooth, with predominantly compact muscle compared to the more trabeculated, mesh-like network in the non-human great apes. The difference is most pronounced at the apex, the bottom of the heart, where we found approximately four times the trabeculation in non-human great apes compared to humans."

The bullseye plots represent the trabecular:compact (T:C) ratio for each segment of the left ventricle. The outer layer of the bullseye plots represents the basal segments, the middle and innermost layers represent the midpapillary and apical segments of the left ventricle, respectively. Red segments correspond to an average T:C ratio of >2; orange segments correspond to an average T:C ratio >1.5–2; yellow segments correspond to an average T:C ratio of >1–1.5; green segments correspond to an average T:C ratio of >0.5–1; blue segments correspond to an average T:C ratio of <0.05. Echocardiographic images of the parasternal short-axis at the apex are shown at end-diastole. *No data were available for the basal or midpapillary segments in the orangutans due to artifact from laryngeal air sacs. †These T:C ratios compare favorably with other reports in healthy human cohorts, ranging from 0.2 to 0.9^65,66. ‡Anatomical labels have been provided in accordance with the conventional guidelines for cardiac chamber quantification by the American Society of Echocardiography and European Association of Cardiovascular Imaging⁵². However, we note that this clinical convention does not align with the recognized anatomical approach and may result in confusion across disciplines—see ref. ⁶⁷ for further clarification.

Cardiac Function and Evolutionary Adaptation

Using speckle-tracking echocardiography, an advanced imaging technique, the team measured the heart's movement and velocities, tracing the pattern of the cardiac muscle as it contracts and relaxes. Curry noted,

"We found that the degree of trabeculation in the heart was related to the amount of deformation, rotation, and twist. In humans, who have the least trabeculation, we observed comparatively greater cardiac function. This finding supports our hypothesis that the human heart may have evolved away from the structure of other non-human great apes to meet the higher demands of humans' unique ecological niche."

Implications for Human Evolution

Higher Metabolic Demand and Thermal Regulation

The study highlights how humans' larger brains and greater physical activity compared to other great apes can be linked to higher metabolic demands. This requires a heart capable of pumping a greater volume of blood to meet these demands. Additionally, higher blood flow contributes to humans' ability to cool down, as blood vessels close to the skin dilate—resulting in skin flushing—and lose heat to the air.

Selective Pressure and Evolutionary Adaptations

Dr. Aimee Drane, Senior Lecturer from the Faculty of Medicine, Health & Life Sciences at Swansea University, remarked,

"In evolutionary terms, our findings may suggest selective pressure was placed on the human heart to adapt to meet the demands of walking upright and managing thermal stress. What remains unclear is how the more trabeculated hearts of non-human great apes may be adaptive to their own ecological niches. Perhaps it's a remaining structure of the ancestral heart, though, in nature, form most often serves a function."

Future Directions

Further Research and Ecological Niches

This study opens new avenues for understanding the evolutionary pressures that shaped the human cardiovascular system. Further research is needed to explore how the heart structure of non-human great apes adapts to their specific ecological niches and how these differences have evolved over time. By continuing to investigate the form and function of the heart across different species, scientists can gain deeper insights into the complex interplay between anatomy, physiology, and evolutionary adaptation.

1. Curry, B. A., Drane, A. L., Atencia, R., Feltrer, Y., Calvi, T., Milnes, E. L., Moittié, S., Weigold, A., Knauf-Witzens, T., Sawung Kusuma, A., Howatson, G., Palmer, C., Stembridge, M. R., Gorzynski, J. E., Eves, N. D., Dawkins, T. G., & Shave, R. E. (2024). Left ventricular trabeculation in Hominidae: divergence of the human cardiac phenotype. Communications Biology, 7(1), 1–9. https://doi.org/10.1038/s42003-024-06280-9