Was reading an excellent post at Watcharama a few days back on the newer 4R movement and how they have evolved from the humble 7s movement, and I decided to do up a movement tree to illustrate the beginnings of some of the popular current day Seiko movements (simple 3 hand variants). The movements include the 7S, 4R, 6R, 4S, 8L and 9S movements, which are all still in production today, except for the 4S, which is now only available with complications. The simple 3 hand 4S15/25/35 movements are no longer in production. The list is obviously not complete, as I had to leave out some movements, including all the chronograph movements (6S and 8R family), but otherwise it is pretty much complete. 6s chronograph is derived from the 4S family, while the 8S chronograph is derived from the 7S family. I have left out all the variants with complications such as GMT, retrograde, power reserve, etc. Quartz, Kinetic and Solar movements are also left out. References from where I got the information can be found at the bottom of this post. Without the information shared by the respective authors of the various posts, I would not have been able to compile this illustration with such ease. 
References:
http://watcharama.com/the-seiko-4r36-family-in-brief/
http://people.timezone.com/library/cjrml/cjrml0024
http://yeomanseiko.com/2009/10/26/grand-seiko-gmt-automatic/#more-599
http://www.seiyajapan.com/pages/the-history-of-grand-seiko
http://www.timekeeper.co.nz/viewtopic.php?f=20&t=763
http://people.timezone.com/msandler/Articles/Workbench/Seiko/Seiko7005.html
musingsofawatchaddict 