You can even download the full length video (I think Part 4 of this docummentary is about the biology of love) if you have Real Player 11 (that comes with Download Manager) installed in your computer, from this link:

http://video.google.com/videoplay?docid=-7364117469621223460

Or, from

http://vodpod.com/watch/427757-the-human-animal-the-biology-of-love-1994-part-four