Here's a few things as a follow up to our final meeting today.
1. Here's Jeff Macmahon's page: http://philosophy.rutgers.edu/FACSTAFF/BIOS/mcmahan.html
He's a rather famous guy these days; he has developed arguments for a view something along the lines of what was suggested by Emerson, namely that beings that are more closely psychologically connected to their futures are more "valuable" than beings that are not connected to the future. He has tons of papers online.
2. Maybe metaphysical issues regarding personal identity have a connection to the morality of abortion. Maybe. See here for more: http://plato.stanford.edu/entries/identity-ethics/
3. Here's some of the research on Marquis's argument about abortion, from the Philosophers Index: