It is important to note that there is no one factor that is responsible for coming up of civilization in one place. Often arguments are put forward for a favorable environment, like a river valley (agriculture). However, we have examples of civilizations which have arisen away from river valleys e.g., meso-American and Minoan Crete. No doubt agriculture was a very important factor, but not the only important one.
An important observation is that all the early civilizations, except the meso-americans, were connected to each other in some way. There is ample evidence of trade between the various civilizations. So, we can safely say that these civilizations benefited from the knowledge of each other.
This is how the book explains the origin:
The most satisfactory answer appears to be that civilization was likely always to result from the coming together of a number of factors predisposing a particular area to throw up something something dense enough to be recognized later as a civilization, but that different environments, different influences from outside and different cultural inheritances from the past mean that men did not move in all parts of the world at the same pace or even towards the same goal.
But another factor was just as important – the capacity of peoples on the spot to take advantage of an environment or rise to a challenge, and here external contacts may be as important as tradition.
However, different civilizations grew at a different pace and in different direction from each other. All developed different forms of culture, art, jewellery, clothing, religion and other artifacts. Inspite of all the differences, one similarity strikes me the most – the manifestation of Gods in the form of elements of nature. It shows the desire of humans to control or influence the elements through various ways.