How evolution shaped the human heart

A recent study has revealed new insights into human evolution by comparing the hearts of humans with those of other great apes.

The research, conducted by an international team, sheds light on how our unique physiological features have developed over time.

Human heart

The human heart is a remarkable organ that pumps blood throughout the body, supplying oxygen and nutrients to tissues while removing waste products.

It is roughly the size of a fist and located in the chest, slightly to the left. The heart has four chambers: two upper atria and two lower ventricles. Blood flows through these chambers, driven by rhythmic contractions of the heart muscle.

The left ventricle, the strongest chamber, pumps oxygen-rich blood to the entire body, while the right ventricle sends oxygen-poor blood to the lungs for oxygenation. The heart’s efficiency and unique structure allow humans to engage in various physical activities and meet high metabolic demands.

Over time, the human heart has evolved to support upright walking and greater physical endurance, distinguishing it from the hearts of other great apes. This evolution has enabled humans to adapt to diverse environments, showcasing the intricate relationship between form and function in this vital organ.

Evolution of the human heart

Despite sharing a common ancestor, humans and non-human great apes have diverged significantly.

Humans have evolved larger brains and the ability to walk upright, which has allowed us to travel long distances, likely for hunting.

Now, researchers from Swansea University and UBC Okanagan (UBCO) believe they have uncovered another piece of the evolutionary puzzle through a comparative study of the heart’s form and function.

Comparing hearts across species

The experts compared the human heart with those of our closest evolutionary relatives, including chimpanzees, orangutans, gorillas, and bonobos.

The research team used echocardiography – a cardiac ultrasound – to produce images of the left ventricle, the chamber of the heart that pumps blood around the body.

During routine veterinary procedures at wildlife sanctuaries in Africa and zoos throughout Europe, the team observed that the non-human great apes had a distinctive feature: bundles of muscle called trabeculations extending into the left ventricle chamber.

“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,” explained Bryony Curry, a PhD student in the School of Health and Exercise Sciences at UBCO.

“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.”

Functional differences

The researchers also measured the heart’s movement and velocities using speckle-tracking echocardiography, an imaging technique that traces the pattern of the cardiac muscle as it contracts and relaxes.

“We found that the degree of trabeculation in the heart was related to the amount of deformation, rotation, and twist. In other words, in humans, who have the least trabeculation, we observed comparatively greater cardiac function,” noted Curry.

“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.”

Human heart’s unique adaptations

Humans’ larger brains and greater physical activity compared to other great apes can be linked to higher metabolic demands, requiring a heart that can pump a greater volume of blood.

This adaptation also contributes to our ability to cool down, as blood vessels close to the skin dilate, observed as flushing of the skin, and lose heat to the air.

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

Heart structure in non-human great apes

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,” said Dr. Drane.

This study opens new avenues for understanding the intricate relationship between form and function in the evolution of the human heart, highlighting the unique adaptations that have enabled humans to thrive in diverse environments.

The study is published in the journal Communications Biology.

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