(Image courtesy of http://neatorama.cachefly.net/images/2007-03/wheel-of-life.jpg)
Have you ever tried googling “life”? I have. This simple word is probably taught in primary schools as property of a living being that distinguishes them from dead organisms or non-living objects. To have life or to be alive generally means being able to grow, and reproduce. But “life” is not that simple to define. Try reading “What is Life?” by Nobel winning physicist Erwin Schrödinger.
My friends and I were enjoying beer while enjoying the sun one Sunday afternoon, as we usually do on Sundays, and a question popped up–how do you define life? As we delved deeper into this subject, I realized I had never examined life in any other perspective than what was taught to me in primary school. As I began pondering on this issue, it became more and more fascinating eventually urging me to share it with the public.
What does it mean to be alive? A few classic properties of “life” are metabolism, growth, reproduction, and response to stimuli. According to Encyclopedia Britannica, life is “further characterized by the presence of complex transformations of organic molecules and by the organization of such molecules into the successively larger units of protoplasm, cells, organs, and organisms.” If these were hallmarks of life, then even the little organic molecules such as DNA and some RNA should be considered alive because provided with right chemicals, they can grow and replicate. Further, even small molecules such as DNA and RNA form complexes such as chromosomes and microRNA and they can even change their structure in response to heat or acidity…thus respond to stimuli.
If that is too severe an example, lets consider prions–the small proteins that can cause other normal proteins to fold improperly thus, causing abnormalities…remember mad-cow disease? How about viruses? Viruses are not considered fully living beings and prions are not even considered living but they both can grow, reproduce, compile and maintain their structures, and respond to their environments.
These classic hallmarks of life do not hold grounds not only in molecular level but also in organism levels. Think about ants and bees…they have drones. Physically the drones are complex, they are capable of metabolsim and growth, and they even have well developed organs. But they cannot reproduce. Can they then be considered alive? This is a subject of discussion for another time.
Life, therefore is much too sophisticated. I am still not clear on how to define “life.” What are some common and fundamental properties of life? May be you can help?