Human evolution: our heart differs from great apes (Introduction)

by David Turell , Sunday, August 25, 2024, 18:47 (22 days ago) @ David Turell

Theirs is trabeculated, ours not:

https://www.sciencealert.com/the-human-heart-is-unique-among-mammals-for-this-key-reason

"...it was believed until recently that the structure and function of the heart across mammals was the same. But research from my colleagues and I reveals that the human heart is an outlier, distinctly different from those of our closest relatives, the great apes, including chimpanzees, bonobos, orangutans and gorillas.

"So, why are humans the odd ones out?

"Humans diverged from chimpanzees (Pan Troglodytes), our last common ancestor, between five and six million years ago. In contrast, people evolved to stand upright to engage in greater amounts of activity, such as persistence hunting. And we have developed considerably larger brains.

"These changes to humans' bodies were associated with a much greater metabolic demand, requiring more blood to be pumped to our muscles and brain. Our research suggests that the human heart has adapted to support our upright stance, movement and larger brain.

***

"Our previous research has suggested that the structure of the human heart may be different to that of the chimpanzee. Using cardiac ultrasound, we discovered that the left ventricle – the heart's main pumping chamber – in chimpanzees contains bundles of muscles arranged in a mesh known as "trabeculations".

"For our current study, we wanted to examine if trabeculations exist in the other great apes, which we found that they do. In contrast, humans have a smooth wall of the left ventricle. This difference is especially pronounced at the bottom of the left ventricle, where the human heart's smoothness is nearly four times greater than that of our great ape relatives.

"Our research didn't just reveal structural differences in the human left ventricle compared to that of the great apes; we also uncovered a important difference in function. By using a specialized technique called "speckle-tracking echocardiography", which tracks heart muscle movement during contraction and relaxation, we examined how the muscle thickens, twists, rotates and lengthens.

"The results were striking. Humans, who have the least trabeculation, exhibited much greater twist and rotation at the apex (the tip of the heart) during contraction. In contrast, non-human great apes, with their heavily trabeculated hearts, showed much less movement.

"We believe the human heart evolved away from the trabeculated structure seen in the other great apes to enhance its ability to twist and contract more efficiently. This increased twisting motion, along with the smooth ventricular walls, probably allows the human heart to pump a larger volume of blood with each beat.

"This meets the heightened demands of our physical activity and larger brains.

"Our research challenges the assumption that heart structure is uniform across mammals. Instead, subtle but crucial differences in heart anatomy and function have emerged in response to unique environmental challenges."

Comment: the left ventricle is the key chamber pumping blood to the whole body. Cardiologists measure how much the left ventricle empties with each beat, normally 67-70 percent of total volume. The original paper did not show those results if performed. The key point is still made, we evolved away from other mammals because of our unusual mobility and exercise capacity.