I mean, he got one when Eve was touching his penis before they ate the apple.
shareI'm not an expert in theology or hermenuetics, but I don't think an erection in itself is considered sinful if it is involuntary or the significance is not understood. I mean, unborn babies in the womb have been known to get them, haven't they?
The only thing that was sinful for Adam & Eve was to eat from the tree of the knowledge of good and evil. There was nothing sinful about him getting an erection.
shareIf you think about it if getting an erection was a sin by itself then the human race would have never got started since sex is usually had with the male having an erection. Since God obviously wanted them to populate the Earth with their children he couldn't xactly say that simply having an erection was sinful. Sometimes the causes for an erection can be sinful. The erection itself is not.
Adam being attracted to and wanting to have sex with his wife would also in and of itself is not a sin either. Forcing your spouse to have sex against their will is a sin. imply wanting to have sex with them is not.