The notion that evolution is completely random, that there is no plan or constraint harmonizes well with the atheistic world view. The fact however is that the commonality of convergent evolution suggests that evolution is a highly constrained process.
Simon Conway Morris has described this argumentation in detail in the book "Life's Solution : Inevitable Humans in a Lonely Universe".
This article discusses the biological factors that contribute to convergent evolution.
"The findings presented in this study also bear directly on issues of convergence (when very different organisms independently evolve similar features). By including a model of development, rather different genotypes can produce very similar phenotypes. Consequently, convergent evolution, which the vast space of genotypes would suggest to be rare, is allowed to become much more common."
