A heart functions as a muscular organ responsible for circulating blood or hemolymph throughout an organism’s circulatory system. While humans and many other animals possess a single heart, the animal kingdom exhibits remarkable diversity in its pumping mechanisms. Some species have evolved to feature multiple hearts or specialized structures that serve similar circulatory roles. These adaptations allow different life forms to efficiently meet their unique physiological demands within varied environments.
Cephalopods and Their Three Hearts
Cephalopods, a group including octopuses, squid, and cuttlefish, are examples of animals with multiple true hearts. These marine invertebrates possess three hearts, each serving a purpose in their sophisticated closed circulatory system. Two are branchial hearts, positioned at the base of the gills. Their function is pumping deoxygenated blood through the gill capillaries for gas exchange and oxygen absorption.
The third heart is the systemic heart, a larger organ located centrally within the mantle cavity. After blood becomes oxygenated in the gills, it flows to the systemic heart. This heart then propels the oxygen-rich blood at high pressure throughout the body, supplying organs and tissues with nutrients and oxygen. This multi-heart system is important for cephalopods due to their active predatory lifestyle and high metabolic rate, requiring efficient oxygen delivery for activities like jet propulsion. Their blood, containing the copper-based protein hemocyanin, is more viscous than vertebrate blood, making multiple pumps advantageous for adequate circulation.
Other Animals with Unique Blood Pumping
Beyond cephalopods, other animals have evolved unique circulatory adaptations that resemble multiple hearts but function differently. Earthworms possess several pairs of structures known as aortic arches, referred to as “pseudohearts.” These five pairs of contractile vessels encircle the esophagus and rhythmically contract to pump blood through the worm’s closed circulatory system. Unlike true hearts with distinct chambers, these arches are specialized, muscularized blood vessels contributing to blood flow.
Insects utilize an open circulatory system where hemolymph circulates within body cavities. Their pumping organ is a dorsal vessel, which runs along their back and acts as a tubular heart. This vessel contracts to move hemolymph forward, but it is supplemented by accessory pulsatile organs in various body parts. These smaller pumps ensure hemolymph reaches the extremities, aiding nutrient and waste transport in areas less efficiently served by the main dorsal vessel.
Why More Hearts Can Be Better
The evolution of multiple hearts or specialized circulatory pumps offers physiological advantages, particularly for animals with high metabolic demands or specific environmental challenges. One benefit is enhanced circulatory efficiency. Having separate pumps can maintain higher blood pressure in different sections of the circulatory system, ensuring a consistent flow of oxygen and nutrients to active tissues. This is important for animals that require rapid bursts of energy or sustained activity.
For example, in cephalopods, the branchial hearts overcome the resistance of pushing blood through the dense gill capillaries, ensuring that the systemic heart receives oxygenated blood at a pressure for distribution throughout the body. This separation of function prevents a single heart from having to perform both high-resistance gill circulation and high-pressure systemic circulation simultaneously, which would reduce overall efficiency.
Such adaptations allow animals to thrive in diverse niches, from the deep sea to terrestrial environments, by tailoring their circulatory systems to their specific needs and lifestyles. While a single heart is adequate for many organisms, multiple or specialized pumps represent an evolutionary solution for demanding physiological requirements.