Dissection Table

If one species have control over the planet earth that is human beings; they are the managers of this planet, at least they think like this. They think they are the only species which can think on its own and to some extent they are rightful in thinking so.

Let us place them on dissection table. Remove their brain and what is left behind is a heap of cells of different kind which are unable to act on their own. Though every cell in this heap is alive and is capable to do many things yet they are so dependent on the instructions coming from brain that they will die waiting for command but will not try to do anything for survival. Though if these cells are provided with the food and oxygen these may live longer. With regard to provision of food these cells are not only able to live on their own rather they can reproduce and even are able to form the whole structure similar to which they were a part of.
We are going too far and my focus for the time being is not to jump to the finality of the discussion rather I want to elongate the discussion therefore I will retract to the whole structure that is the body of human beings. Brain is specialized structure to rule over the body and other parts obey the commands so dispatched to them; hands and feet are specialized to reach to places and perform jobs so as to make food available to the body and Digestive & Respiratory systems are specialized to process the food and make it available to each cell in the final consumable fuel shape, blood cells perform activity of carrier of food. The cells has their own burning units which burn the final consumable fuel & get essentials for keep the life on.
If we look at a human being in isolation it is a sustainable machine, but every machine is subjected to wear and tear and so is human being. A machine that uses energy and that performs functions is inevitable to wear out some of its parts which might collapse the whole system. The machine is self aware and knows eventually it will be destroyed due to one or other reason therefore it will try its best to generate its alternate during its working/life span. Yes, reproduction is the process by which human being creates its replacement. The process of generating new machines by the old machines is not limited to human beings only rather all other machines on the crust of earth pass through the same phase.
There are some limitations in the system as the plant used to produce new machines is not capable to produce alike machines rather it produces smaller versions which eventually grow into the bigger ones by consuming fuel.