Cutting through the obligatory evolutionary ranting here, I think it's some pretty cool stuff. Basically, during the first stage in placental development, we activate primarily genes shared by other species. But in the second portion, we activate species-specific genes.
How cool is that?
The evolutionary error, of course, is to conclude from these facts that all the species are related. No go. Just because the Model T and the Highlander Hybrid both have tires doesn't mean they're related. But it's still really cool. I'm interested in what gene (or other biological structure) controls the activation of the genes within the two stages. How does the embryo "know" when different genes need to be activated?