Footnotes

• Contributors BS came up with the idea of writing this commentary and, following discussions between all the authors, drew up a general sketch of what was to be written. FGdF was responsible for researching and writing the larger part of the text regarding issues surrounding human spermatogenesis and epigenetics, and providing the references for the remarks on the subject. BS and DMR were responsible for drafting the (brief) ethical commentaries concerning the practical limitations of in vitro breeding of human gametes. NPC and DMR, under supervision by BS, were responsible for reporting and structuring the arguments and revising the language for the final draft. FGdF and BS are responsible for the overall content as guarantors.

• Competing interests None.

• Provenance and peer review Commissioned; internally peer reviewed.