An international research team from UBC Okanagan and Swansea University has uncovered a new insight into human evolution by comparing the hearts of humans with those of other great apes.
While humans evolved to travel long distances and likely hunt, other great apes evolved to meet the demands of their immediate forest environment, seeking shade when they overheated, explains Bryony Curry, a doctoral student at UBCO’s School of Health and Exercise Sciences.
The greater bipedal locomotion and larger brain of the human species are two pieces in the puzzle that explain humanity’s evolutionary divergence from its common ancestor.
Now, through a comparative study examining the differences between the human heart and those of several primates, researchers think they may have found a new piece of the puzzle about how the hearts of primates and humans have developed differently over time. amended.
The international study, published in Nature’s Communication Biology, compared the human heart to that of chimpanzees, orangutans, gorillas and bonobos. These non-human great apes share more than 98 percent of their DNA with humans, making them humanity’s closest evolutionary relatives.
The non-human great apes were cared for in nature reserves in Africa and European zoos. During routine veterinary procedures, the team used echocardiography – a cardiac ultrasound – to create images of the great apes’ left ventricle, the left chamber of the heart.
In the left ventricle there are muscle bundles called trabeculations that extend into the ventricle.
“The left ventricle of a healthy human is relatively smooth, with compact muscles compared to the more trabeculous, mesh-like network in the non-human great apes,” Curry explains. “The difference is most pronounced at the top or bottom of the heart, where we found about four times as much trabeculation in non-human apes as in humans.”
The team also examined the twisting and turning of the heart. When a heart contracts, it deforms and then springs back to its original shape. The researchers measured this deformation and the speed of this movement using an imaging technique called speckle-tracking echocardiography, which follows the speckled pattern of the heart tissue as it contracts and relaxes.
“We found that the degree of trabeculation in the heart is related to the amount of deformation, rotation and twisting,” says Curry. “In humans, we have observed that their hearts have the greatest function with the least trabeculation. 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 our unique ecological niche.”
Curry explains that humans have larger brains and are also more physically active compared to other great apes, which equates to a higher metabolic demand. This requires a heart that can pump a relatively larger volume of blood to the body. Higher blood flow also contributes to humans’ ability to cool down as the blood vessels close to the skin dilate (skin is observed to redden) and lose heat to the air.
“In evolutionary terms, our findings suggest that selective pressure was placed on the human heart to adapt so that it can meet the demands of upright walking and managing thermal stress,” adds Dr. Robert Shave, Associate Dean of Research at UBCO’s Faculty of Health and Human Services. Development. “What remains unclear is how the more trabeculated hearts of non-human great apes might adapt to their own ecological niches. Perhaps it is a rudimentary structure of the ancestral heart, although in nature the shape usually serves a function.”
