Empirical studies such as Goyal, van der Leij and Moraga (2006) or Newman (2004) show that scientific collaboration networks present a highly unequal and hierarchical distribution of links. This implies that some researchers can be much more active and productive than others and, consequently, they can enjoy a much better scientific eputation. One may think that big intrinsical differences among researchers can constitute the main driving force behind these huge inequalities. We propose a model that show how almost identical individuals self-organize themselves in a very unequal and hierarchical structure as is observed in the real-world co-authorship networks. In consequence, this model provides an incentives-based explanation of that empirical evidence.