Why don’t we have 2 Hearts or 2 Brains?

posted in: Science & Facts | 0

Life has started on earth 550 million years ago. Although many theories exist simplifying the mystery of life, it has been always complex to understand the evolution of organisms. 2 Hearts ! 2 Brains! There is nothing impossible for nature and evolution. There are animals with multiple Hearts and Brains. An Earthworm has 5 hearts while the Leeches have 32 Brains!!! Apart from 32 Brains, Leeches have 3 mouths and each mouth is having 100’s of teeth. Not only them, they are many animals in the list having multiple organs which can be googled easily. However, humans don’t have backups like them. We have only 1 Heart and 1 Brain. But Why?? Let’s explore the reasons behind this…

Pictures of Earthworm and Leech

One of the popular theories is Bilateral Symmetry theory. I have explained about this in my last post. Just to brief, Bilateral organisms are those which looks symmetrical on both left-hand and right-hand sides with respect to a line drawn vertically in the middle.

Human muscular picture showing Bilateral Symmetry with a vertical imaginary line drawn in middle.

Life, as predicted by many theories, first came into existence in water bodies. Slowly the first creatures began to move and wander in water. With time and evolution, they came out of the water and started life on the land 330 million years ago. Unlike swimming in the water, movement on land requires proper balance and structure. So, these organisms developed a bilateral body which is symmetrical about lateral or vertical section.

Water Organism evolving to Land Organism. Representational Image.

This symmetry along with various physical factors on land like gravity, helped in forming limbs and bones giving a proper structure, eventually resulting in balanced movement on the land surface. To attain this symmetry, humans might have developed few organs in pains while few in single.


The Fetus of the human being in mother’s womb develops organs as BUDS along the Spine. These buds grow to from organs like lungs, heart, liver, kidneys etc. While BUD formation Heart also develops 2 buds like lungs and kidneys. Along the spine 2 buds of lungs are separated by a distance while 2 buds of the heart are close to each other. In fetus growth process, as these 2 heart buds are closer to each other they merge and give a single unit. That’s why we have a single Heart. Brain from the beginning is a single bud. This theory applies to other single organs too.

Fetus developing Organ BUDS

The explanation above just answer why we have only 1 heart, but there is one more underlying question. “Why do those fusion buds only form the heart and why not others?”

Well. It’s nature which made us in this way. Earthworm has 5 hearts because it needs five. Our body might be needing only one according to our genes and body condition. If habitat of humans change, after few more million years we might also have a body suitable for those new conditions have multiple organs and different structure. For now, for this environment, this is the most suitable structure (Nature belief). Science has no further explanation for this question.

Thank You!


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