Was Human Life Dependent on Five "Hard Steps"?

I wish I knew! THIS PAPER suggests not, but first of all - What Are The Five Steps? They are the things which had to happen for human life to exist. And it is soon evident that much academic blood has been spilled over the compilation of the list. But here is one version of it.

1. Life (abiogenesis)
   
   
2. Oxygenic photosynthesis
   
   
3. Eukaryotic cells - fusion of a Bacteria with an Archaea
   
   
4. Animal multicellularity
   
   
5. Homo sapiens

The order of the steps is fixed. Steps 1, 3 and 4 are evolutionary steps, 2 and 5 are not. Various other steps have been proposed but five seems a good number. A definition of a hard step is:- Improbable, and essential for the evolution of humanity.

These hard steps are fairly evenly distributed over the life of the Earth.

The authors of this article suggest that these singularities are the result of the global-enviromental processes. They may have happened once but the happening was inevitable.

This is a very interesting article and you need to read it to get an appreciation of the knowledge used in it. But the conclusion seems to imply that human like beings should be fairly common in the universe. So far we have discovered only us. Are the authors wrong or is there something preventing intragalactic communication?