Board Thread:Warhammer 40k General Discussion/@comment-20282318-20140210075721/@comment-16400780-20171220175410

Timjames98 wrote:

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Anatomy: As for acts, their Gigantism tends to complicate this. If the partner was a normal human woman and the Space Marine was a loyalist then I imagine that the Space Marine would have to be REALLY careful (especially if they tried doing traditional intercourse instead of just sticking to carassing and non-traditional sex acts). Of course Traitor Space Marines from Slaneeshi and Undivided Warbands might be willing to copulate with Deamonettes and Xenos and would almost certianly not be careful (or worse yet, might intentionally attempt to hurt their partners). Nurgling Marines would be too rotted, Khornite Marines would be too focused on violence, and Tzeenchian Mariens would be too focused on schemes.

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Sexual Reproduction: On reproduction, I think that virtually all Space Marines will never be fathers. They weren't made to reproduce, and the closest they come to reproduction is when they pass their geneseed to new initiates, so I'd say that the process makes them sterile. Salamanders have children and families, but I think that's due to other factors (adoption, sexually reproducing BEFORE they get their geneseed installed, artificial insemination, etc). Even then I think that Salamanders who do have children often have very little interaction with them due to long campaigns: if you're dad's a Salamander then you might see him once as a baby before he goes on campaign ... and if you're luck you'll see him again as a 90 year old man when he returns in between campaigns ... then you're great-great grandson will see try to pass initiation and if he passes than he MIGHT meet up with your father again. Your assume that the space marine will also have gigant penis, but I can easily imaging that it wouldn't be as 'enhanced' as the rest of the body. I admit I haven't read anything to support this.

According to the chart on Gene-Seed the process of making a space marine starts at 10-12 years, so while sexual production before could be possible it seems very unlikely.