I'm merely reporting this primer, and at the same time a couple of "quick guides" in the same journal on the vexed issue of contingency vs. convergence in evolution. Simon Conway-Morris (the author of the second quick guide) is a fierce advocate of convergence. He has been one of the main investigators of the Burgess Shale fossils which led to very different interpretations: ironically, Stephen Jay Gould took them as a sign of contingency (phyla live and die more or less at random) when Conway-Morris took them to support convergence (because of the common points between the different phyla discovered).

Anyway. The issue is far from being settled, but one of the advantages of a strong "convergentist" stance is that it allows funny speculations about ET: if convergence is a strong driving force in evolution then living things on other planets should share a lot of attribute with us (from the molecules implied in vision to the evolution of morality). In fact they may be so similar to us that they may be among us already and nobody would have noticed...