Studying the architecture of the heart offers a new understanding of human evolution

An international research team from Swansea University and UBC Okanagan (UBCO) has revealed new insights into human evolution by comparing human hearts with those of other great apes.

Despite the fact that humans and apes share a common ancestor, the former developed a larger brain and the ability to walk or run upright on two legs to travel long distances, probably to hunt.

Now, through a new comparative study of heart form and function, published in Communication biologyscientists believe they have discovered another piece of the evolutionary puzzle.

The team compared human hearts to those of our closest evolutionary relatives, including chimpanzees, orangutans, gorillas and bonobos, which are cared for in wildlife reserves in Africa and zoos across Europe.

During routine veterinary procedures for these great apes, the team used echocardiography — an ultrasound of the heart — to create images of the left ventricle, the chamber of the heart that pumps blood around the body. Inside the left ventricle of great apes, bundles of muscles called trabeculae extend into the ventricle.

Bryony Curry, Ph.D. student in the School of Health and Exercise Sciences at UBCO, said, “The left ventricle of a healthy human is relatively smooth, with predominantly compact muscle, compared to the more trabeculated meshwork of great apes.”

“The difference is most pronounced at the apex, the bottom of the heart, where we found approximately four times more trabeculation in apes compared to humans.”

The team also measured the heart’s motion and speeds using speckle-tracking echocardiography, an imaging technique that tracks the pattern of the heart muscle as it contracts and relaxes.

Curry said: “We found that the degree of trabeculation in the heart was related to the degree of deformation, rotation and twisting. In other words, we observed comparatively greater heart function in people who had the least trabeculation. This finding supports our hypothesis that the human heart may have evolve outside the structure of other non-human apes to meet the higher demands of humans’ unique ecological niche.”

Humans’ larger brains and greater physical activity compared to other apes may also be associated with higher metabolic demands, requiring a heart that can pump a larger volume of blood around the body.

Similarly, higher blood flow contributes to a person’s ability to cool down, as blood vessels near the skin dilate—observed as reddening of the skin—and lose heat to the air.

Dr. Aimee Drane, senior lecturer in the Faculty of Medicine, Health & Life Sciences at Swansea University, said: “In evolutionary terms, our findings may suggest that there has been selective pressure on the human heart to adapt to the demands of walking upright and coping with heat stress.

“It remains unclear how the more trabeculated hearts of great apes can adapt to their own ecological niches. Perhaps this is a remnant structure of the ancestral heart, although in nature the form most often serves a function.”

The research team is grateful to the staff and volunteers who care for the animals in the study, including teams at Tchimpounga Wildlife Sanctuary (Congo), Chimfunshi Wildlife Sanctuary (Zambia), Tacugama Chimpanzee Sanctuary (Sierra Leone), Nyaru Menteng Orangutan Rescue and Rehabilitation Center (Borneo ), Zoological Society of London (UK), Paignton Zoo (UK), Bristol Zoo Gardens (UK), Burgers’ Zoo (Netherlands) and Wilhelma Zoo (Germany).