Researchers have discovered a feature that clearly distinguishes humans from animals: a heart that can pump a particularly large amount of blood. It is an evolutionary adaptation to our large brains and our need for movement.
It helped hunters and gatherers when they ran after their prey: the human heart.
Annick Ramp / NZZ
What distinguishes humans from chimpanzees? Their inhibitions, said the Bernese chansonnier Mani Matter. Aristotle, however, was convinced that it was language. One could also cite upright posture or a large brain. But now an international research team has identified another organ that is said to make our species unique: the heart.
Until now, it was assumed that the hearts of all mammals are quite similar. According to the new study The human heart differs significantly from that of our closest relatives, the great apes. It has structural peculiarities in the left ventricle, and the heart muscle contracts differently. This is evidently an adaptation to our active life on two legs and to our large brain: the human heart can pump more blood to meet the increased energy requirements.
A visit to the zoo shows that great apes have different physical characteristics to us. “There you can see that chimpanzees only sprint for a short time, then they are completely out of breath,” explains Aimee Drane, a cardiac physiologist at Swansea University and co-author of the study. “They are simply not made for running.” Humans are completely different. They have several characteristics that make them excellent long-distance runners: their long legs, their enduring muscles, and skin full of sweat glands instead of fur. The human heart is another piece of the puzzle of this machinery, says Drane.
Cardiac ultrasound in chimpanzees
Our ancestors were hunters and gatherers for hundreds of thousands of years. In order to track their prey or search for plant-based food, they had to be active for hours. In order to ensure that the muscles were constantly supplied with enough energy, they needed a heart that could pump a lot of blood. The typical physical exertion of a great ape – climbing a tree, chasing away a fellow ape – takes much less time. Their hearts are heavily strained, but only for a very short time.
The researchers led by Aimee Drane compared the human heart with those of great apes. They examined chimpanzees, bonobos, gorillas and orangutans that live in wildlife sanctuaries in Africa or in zoos in Europe. Using cardiac ultrasound, the scientists created images of the left ventricle, which pumps blood into the aorta and thus through the body. Using an additional imaging technique, they tracked the pattern of the heart muscle as it contracted and relaxed.
They discovered that the heart chambers of monkeys are much more densely traversed by so-called trabeculae than those of humans. These are bundles of muscles arranged like a kind of net. The left ventricle of a healthy person, on the other hand, is smooth, with predominantly compact muscles. The difference is most obvious at the apex, the lower part of the heart. The human ventricle is also slightly larger.
“We found the pronounced trabeculae in all great apes, young and old,” says Drane. Perhaps even more important, however, are the differences in heart function. The research team found that the human heart also twists when it contracts. “If this twisting is released during the relaxation phase, the heart can suck in a lot of blood, which it then pumps during the next contraction,” explains Drane. No such twisting movement occurs in great apes.
While the hearts of great apes with their trabeculae have thicker walls and are therefore well suited to dealing with short-term high blood pressure, the human heart with its high pumping capacity ensures the body’s constant energy supply.
The red head after jogging
According to Drane, the cardiovascular system benefits endurance athletes in another way. In addition to sweating, blood flow contributes to cooling: when the blood vessels expand near the skin, heat is released into the air. This is also why you get a red head after a summer jog.
Other animals cannot rely on this cooling function. This is crucial for hunting in the African savannah, which was not only practiced by modern hunters and gatherers, but also by our ancestors: humans can pursue prey such as gazelles until they overheat and collapse.
But if the human heart pumps so much more blood than that of our closest relatives, does it not need additional adaptations in the cardiovascular system? Apparently so, as another research group was recently able to show. She took a closer look at the part of the body that is directly connected to the heart: the aorta. In fact, this blood vessel is significantly larger in our species than in the great apes. And these researchers also come to the conclusion that the large brain and the energetically demanding lifestyle of humans require the increased blood flow.
Monkey-like heart in sports-haters
Previously, Aimee Drane and her colleagues also found that there are significant differences in the structure of the heart among people, although these depend on lifestyle. The scientists examined the heart structure of endurance athletes and people who hardly do any physical activity. It was found that athletes have longer, larger and more elastic left ventricles. In contrast, untrained people often have a more ape-like heart with thicker and less flexible walls even at a young age.
This clearly shows how regular exercise keeps us healthy – and that too little of it is harmful: “If large amounts of blood do not flow regularly through our heart and our blood vessels, they begin to stiffen,” says Drane. This leads to higher blood pressure, which in turn can cause cardiac arrhythmia.
The researchers’ findings suggest that the process of developing hypertension begins years before it is first diagnosed in a doctor’s office. The problem is widespread, as Figures from the World Health Organization 31 percent of adults worldwide do not achieve the recommended 150 minutes of moderate-intensity physical activity per week. About a quarter of them have high blood pressure.
This is why Drane appeals: Even if it is better to exercise throughout your life, it is never too late to start. “Sport is always useful for us humans,” she says. After all, we are naturally made for it – including our unique hearts.
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