In ancient Egypt, when kings and queens were mummified, their brains and internal organs were removed, except for one: the heart. Egyptians believed the heart was the center of thought and emotion, and that it was needed in the afterlife. By around 2000 BC, Chinese doctors discovered that the heart’s main job was to pump blood throughout the body. However, many Western thinkers, like Aristotle, believed the heart controlled emotions, a belief that has lingered in different forms even today.
The heart symbol we know today doesn’t look much like the real organ, and its origins are a bit of a mystery. It first appeared around the 6th century BC on coins from Cyrene, an ancient city in what is now Libya. These coins featured the heart shape to represent silphium, a plant used for cooking, perfume, and even as a contraceptive. In the 17th century, St. Mary Margaret Alacoque had a vision of the sacred heart of Jesus, surrounded by thorns, which linked the heart symbol with love and devotion.
Today, we understand that love and emotions come from the brain, not the heart. Although saying “I love you with all my limbic system” might not sound romantic, the feelings are very real. Emotional pain can activate the same brain areas as physical pain, causing symptoms like nausea and dizziness, which is why heartbreak can feel so intense.
When we see someone we love, our brain releases chemicals that make our heart beat faster. But too much excitement can be dangerous; a heart rate of 200 to 250 beats per minute is risky for humans. Interestingly, a tiny animal called the pygmy shrew has a resting heart rate of 1300 beats per minute, much faster than a human’s.
Despite their short lifespan of about a year and a half, a pygmy shrew’s heart beats around a billion times. Surprisingly, many animals, regardless of size, seem to have about a billion heartbeats in their lifetime. This isn’t just a countdown to the end; it’s part of a fascinating biological pattern.
Smaller animals lose heat faster than larger ones, leading to higher metabolic rates and quicker cellular wear. Scientists have found that animals with lower metabolic rates tend to live longer. As animals get bigger, their heart rates slow down, following a pattern called the quarter-power scaling principle. For example, a cat is about 100 times more massive than a mouse, and its heart beats about one-third as fast. This principle also applies to lifespan; larger animals tend to live longer.
Humans, however, are an exception. We live about three times longer than expected for our size and have more heartbeats than anticipated. Thanks to modern science and medicine, as well as taking care of each other, we can enjoy longer, healthier lives.
Measure your heart rate at rest and after physical activity. Compare your results with classmates and discuss how different activities affect heart rate. Consider why the heart rate increases and what this tells us about the heart’s role in the body.
Create an art piece that incorporates the heart symbol. Research its historical origins and significance, and present your artwork along with a short explanation of how the symbol has evolved over time.
Engage in a class discussion about how emotions are processed in the brain. Explore why the heart is often associated with emotions and share your thoughts on how this perception has changed with scientific understanding.
Research the heart rates of different animals and create a chart to compare them. Discuss the quarter-power scaling principle and how it relates to the lifespan and size of various animals, including humans.
In groups, role-play a debate between ancient Egyptian, Chinese, and Western thinkers about the heart’s function. Use historical context to support your arguments and reflect on how these beliefs influenced their cultures.
When mummifying their kings and queens, ancient Egyptians would remove the brain and all internal organs, except for one: the heart. They believed it held all thought and feeling, and the deceased would need it in the afterlife when they rose again. By 2000 BC, Chinese doctors had uncovered the heart’s role in pumping blood throughout the body. However, Western thinkers from Aristotle to the Renaissance believed the heart governed emotions, a notion that still persists today, albeit in a different form.
The heart symbol’s resemblance to the actual organ is debatable, and its origins are uncertain. We see it as far back as the 6th century BC, with coins from Cyrene, in what is now Libya, carrying the familiar emblem, which represented silphium, a now-extinct plant used as a cooking spice, perfume, aphrodisiac, and contraceptive. In the 17th century, St. Mary Margaret Alacoque reported seeing a vision of the sacred heart of Jesus, surrounded by thorns, and the symbol has since been associated with love and devotion.
Today, we know that love, along with all of our thoughts, desires, and emotions, comes from our brain, not our chest. While it may not sound as romantic to say “I love you with all my limbic system,” the feelings we experience are very real. Physical pain activates the same regions of our brain as emotional loss. This neurological stress can overstimulate the body’s vagus nerve, causing nausea, dizziness, and physical pain—real heartbreak.
However, there are positive aspects as well. When we see a loved one, our brain stimulates the release of epinephrine and norepinephrine from our adrenal glands, causing our heart to beat faster. Yet, one can desire too much of a good thing; heart rates of 200 to 250 beats per minute could be dangerous for humans, but for a pygmy shrew, that would feel tame. This tiny relative of the mole has a resting heart rate of 1300 beats per minute, surpassing even a hummingbird’s rapid heartbeat and more than 15 times the average human’s.
A pygmy shrew will live just a year and a half, but in that time, their heart will beat about a billion times. An elephant? About a billion beats. A rabbit? About a billion. In fact, animals of all sizes seem to get about a billion heartbeats in a lifetime. The heart isn’t merely a ticking clock counting down to the end, but there is some truth to the billion heartbeat hypothesis.
Because they have a larger ratio of surface area to mass, small animals lose heat more quickly than larger animals, leading to higher metabolic rates and quicker cellular wear. Scientists believe that lower metabolic rates are directly linked with longer lifespans. As mass increases, heart rates scale to the minus one-fourth power. For example, a cat is about 100 times more massive than a mouse, and its heart beats about one-third as fast. This principle also applies to lifespan; larger mass scales to the positive one-fourth power. That cat, being 100 times larger than the mouse, lives about three times as long.
Biologists refer to this as the quarter-power scaling principle, where measures of metabolism scale in multiples of one-fourth for different-sized animals. However, humans seem to be an outlier. Following that rule of size, we live about three times longer than expected and have about twice as many heartbeats as one would anticipate. The advancements of modern science and medicine have extended our lifespans, and caring for one another helps us live longer.
Heart – The muscular organ in humans and other animals that pumps blood through the circulatory system by rhythmic contraction and dilation. – The human heart beats approximately 100,000 times a day to circulate blood throughout the body.
Egypt – An ancient civilization in northeastern Africa, known for its pyramids, pharaohs, and significant contributions to human history. – Ancient Egypt is famous for its monumental architecture, including the Great Pyramid of Giza.
Emotions – Complex psychological states that involve three distinct components: a subjective experience, a physiological response, and a behavioral or expressive response. – The study of emotions in animals can provide insights into their behavior and social interactions.
Brain – The organ in the head of humans and other vertebrates that is the center of the nervous system, responsible for processing sensory information and controlling behavior. – The human brain is capable of forming new connections, which is essential for learning and memory.
Love – A strong feeling of affection and care towards someone or something, often considered a complex emotion influenced by biological, psychological, and social factors. – In history, love has been a powerful motivator for actions and decisions, influencing events and cultures.
Animals – Multicellular, eukaryotic organisms that form the biological kingdom Animalia, characterized by their ability to move, consume organic material, and respond to their environment. – Animals play crucial roles in ecosystems, acting as predators, prey, and pollinators.
Science – The systematic study of the structure and behavior of the physical and natural world through observation and experimentation. – Science has helped us understand the processes of life, from the cellular level to entire ecosystems.
Beats – The rhythmic contraction and relaxation of the heart muscle, which pumps blood throughout the body. – The doctor listened to the patient’s heartbeats to ensure they were regular and strong.
Lifespan – The length of time for which a person or animal lives or a thing functions. – The lifespan of a tortoise can exceed 100 years, making them one of the longest-living animals.
Metabolism – The set of life-sustaining chemical reactions in organisms that convert food into energy, build and repair tissues, and eliminate waste products. – A person’s metabolism can affect how quickly they gain or lose weight.
