In 18 th century, Darwin proposed a theory called “survival of the fittest” . This theory holds true in context of humans. We humans are the most intelligent species on earth...! Humans have used their intelligence over the years to dominate other species on earth and also dominate the fellow humans as well. We are proven as dominant to most of the species on earth. That's why, our population is ever increasing on earth. But there's another theory, called as balance of nature theory , which says "ecological systems are usually in a stable equilibrium or homeostasis, which means that a small change, like the size of a particular population, for example, will be corrected by some negative feedback that will bring the ecosystem back to its original “point of balance” with the rest of the system". The dominance of humans now is challenged by a negative feedback, in the form of a small virus, to bring back ecosystem back to the original ...