Then we understand plants are life too and discovered million millions of micro-organisms. Now we know how life is certain complex set of chemical processes and how it evolved from simple form such as bacteria to plants, fishes to animals including humans through natural selection process. The evolution of life is as much proved as the earth is spherical not flat. We know the life's secret genetic molecule, the DNA and its four letters genetic code (A, C, G, and T), the same code that connects all living species on the earth! We can artificially create all the ingredients of living cell including DNA. For research purpose, scientists brought back a long-vanished 1918 flu virus that killed up to 50 million people back to life. Technically we can take a cell from our body and create any organ or another cloned individual.
As we understand the basics of life, people slowly moved the concept of soul to our mind. This idea was thrived from the concept of mind-body dualism. People thought mind was totally different from the physical body, the brain (people also used to think that the heart was the center of soul, spirit and love), and perhaps the brain somehow linked to the soul to give raise to the mind. Many bizarre mind phenomena such as near-death experience and out-of-body experience also fueled this view.
As walking emerges when our legs function, our mind emerges when our brain functions. Now we can watch our brain live when it is working in fMRI (functional Magnetic Resonance Imaging) machines. We know where our different senses are processed, how emotions are handled, and the pathways of how short-term memory (episodic memory) becomes long-term memory. Now we can explain better about many bizarre mind phenomena including near-death experience (light at the end of the tunnel syndrome) and out-of-body experience (it is better to say, out-of-body illusion). We can stimulate out-of-body experience by simply inducing our brain with magnetic pulses!
Our brain is divided into two hemispheres: right and left. The right hemisphere takes care of left side of our body and the left hemisphere takes care of right side of our body. Both hemispheres are connected with a bundle of fibers known as Corpus Callosum. In many respect, these two hemispheres can be considered as two different brains. When the Corpus Callosum is removed for some reasons, we can notice how these two hemispheres are different in their preferences, choices, desires, beliefs, etc. For example, there are patients with this condition say, they believe in God from one side of the hemisphere and do not believe in God from other side of the hemisphere (this can be done by closing one eye as each eye is processed by different hemispheres). If there is such a thing as soul, in this case it should have been halved (and perhaps one part of the soul will go to heaven and the other part will go to hell!).
Nevertheless in a different sense, the soul still exists in a real sense! It is an essence that emerges from something, say a book, a movie, an animal or a human (the soul of a book or movie). It is like a picture that emerges from collection of tiny pixels; it is like a story in a book that emerges from collection letters; and it is like a living cell emerges from collection of chemical processes. A single living cell is punch of chemical processes with no feeling or anything of a human. But our mind with feeling, hopes and desires, pain and pleasure emerges from collection of these cells! That is the soul of an individual person!
What we do that is essentially different from other animals? Other animals too form groups, love others and fight with others, seek food, seek mate and have sex, fall in love and form family, reproduce and take care of their children, and ultimately get old and die. We are not the biggest animal; we are not the strongest animal; or even the fastest animal! Then, what makes us different? It is our drive to understand the world we live in! This is what enabled us to predict weather and cultivate agriculture; this is what enabled us to reach the moon! That is the soul of our human species!