I wouldn't exactly call this a "theory". More like a long-standing suspicion/notion/hunch that I've had. Of course I have a long penis and tend to have girls. Has anybody here also wondered if a deeper ejaculation (which does, of course, go hand in hand with a longer penis) increase the chances of a girl being conceived rather than a boy? Has anybody heard of any research into this? I want to point out that this supposed "long-penis = girls" phenomenon (if it exists) would only apply in relation to the length of the woman's vagina. So, if we had a population whose average penis length was relatively long, it might not matter if the average vagina was also long. So, before y'all attack me for "bad science", please note that I'm not claiming it as "science", just an idea I've entertained for quite some time.