BOSTON — Within the hierarchy of nature, humans have certainly never been the strongest creatures. Mankind’s major advantages over the animal kingdom can be summed up in two words: intelligence and mobility. Besides just evading predators, for centuries virtually all humans sustained themselves by hunting and farming, two activities that necessitate long periods of physical exertion. As such, a new study confirms the human heart evolved over time for endurance, slowly becoming less and less “ape-like,” in reference to our evolutionary ancestors.
So, because the human heart is intended for endurance activities, those who live a largely sedentary lifestyle are at a much greater risk of developing heart disease, researchers say.
That’s the main takeaway from a recent study conducted at Massachusetts General Hospital, and researchers even went so far as to say that individuals who neglect their physical fitness actually have hearts that are more “ape-like.” The study’s authors investigated the differences between human and ape hearts, the reasons for these differences, and what these observations mean to human heart health.
To accomplish this, the heart functioning of apes was compared to four distinct groups of humans, ranging from individuals classified as “elite runners,” to those who rarely exercise at all.
Chimpanzees are considered human’s closest evolutionary relatives, but there are quite a lot of differences among the two species. Chimpanzees largely sustain themselves and live through short bursts of energy (climbing), only putting their hearts to work for short periods of time. Conversely, it’s generally accepted that up until the Industrial Revolution most humans had to be active and moving for most of the day hunting and farming. In order for pre-industrial humans to survive, they essentially had to engage in endurance activity on a daily basis.
These varying types of activities induce different physical changes in the heart. Endurance activities, like walking and running, cause the heart to pump more blood throughout the body to deliver fuel to muscles. On the other hand, shorter bursts of activity put more overall pressure on the heart, which over time causes the heart chambers to stiffen and become thicker.
“The heart remodels in response to two main forces: pressure and volume,” comments MGH director Dr. Aaron L. Baggish in a release. “Humans have longer, thinner- and more flexible-walled hearts, while chimps have smaller hearts with thicker walls.”
For the research, a group of 160 participants was gathered. Each person’s heart was extensively studied, including blood pressure readings, as well as ultrasound examinations of heart structure and functioning during a variety of activities. The studied participants were selected based on their jobs and activity levels, and evenly separated into four groups: elite runners, American football players, indigenous Mexican subsistence farmers, and people who rarely exercise / engage in physical exertion. Similar heart readings were also taken among a group of 40 chimpanzees and five gorillas.
“The goal was to compare heart structure and function in each ‘type’ – whether the subject was very active, to barely active,” Dr. Baggish explains.
Overall, researchers found that the human heart has in fact evolved over time to be better suited for endurance activities instead of shorter bursts of intense energy exertion. Moreover, people who regularly engage in such activities, such as runners, have longer, larger, and more elastic left ventricles, meaning their heart can more efficiently pump blood throughout their body. On the other hand, people who don’t engage in endurance activities very often have hearts that appear to be more “ape-like,” meaning their hearts are much better at dealing with short periods of physical activity. This observation held true even among sedentary-lifestyle individuals who were of a young age.
“The human heart has evolved over hundreds of thousands of years as our activity levels gradually became more sustained,” Dr. Baggish says. “We now understand that the human heart, coupled with changes in the musculoskeletal and thermoregulatory system, evolved to facilitate extended endurance activity rather than spurts of intense exertion.”
These findings have a number of major implications for how the medical community understands and approaches human heart health. For instance, based on this study, people with a more lazy lifestyle are much more prone to high blood pressure, which can in turn result in more serious forms of heart disease.
The study is published in the Proceedings of the National Academy of Sciences.