לזכות ר' משה מרדכי בן חנה לבריאות השלימה
The Rambam says that an אנדורגינוס requires a bris milah מספק but no bracha is made. The Raavad differs and says that a bracha must be made.
The Acharonim [such as Rav Berel Kroizer ztz"l in his Shiurei Dvar Hamelech and Rav Moshe Avigdor Amiel in his Darkei Moshe] learn that they are arguing about the nature of the obligation to fulfill mitzvos out of doubt. The Rambam holds that even when we are required to fulfill a mitzva out of doubt, nevertheless the obligation remains doubtful. So we tell the person to fulfill the mitzva but not to make a bracha in order to avoid a bracha li-vatala. The Ra'avad argues with the Rambam [that is what he did for a living:-)] and says that when a person has a doubt as to whether he must fulfill a mitzva, the Rabbis placed upon him an absolute, clear obligation to fulfill the mitzva. This doubt creates a NEW obligation thus necessitating a bracha.
In summation - the Rambam holds that a safek mitzva mitzva must be done מתורת ספק while the Raavad holds that a safek mitzva must be done מתורת ודאי.
The Pri Megadim [Orach Chaim 17/2] says that according to the Rambam who holds that ספיקא דאורייתא is לקולא according to the Torah [and there is now only a Rabbinic obligation] a woman may be מוציא a טומטום in bentching because her דרבנן is מוציא his דרבנן. But wait a minute!! Maybe this טומטום is really a man and is חייב מדאורייתא and the woman is really a woman [she is!] and might only be חייבת מדרבנן so how can she be מוציא him?
We are compelled to say [and so said the sefer חדוותא דשמעתתא] that the Pri Megadim holds that according to the Rambam, if one is not sure about a חיוב דאורייתא there is no longer a חיוב. He is off the hook completely because ספק דאורייתא לקולא מן התורה. Now the Rabbis came along and said that there is a new Rabbinic obligation to do the mitzva. So we have no doubt anymore - a woman can be מוציא a טומטום because they both have an absolute Rabbinic obligation.
But that is not consistent with our understanding of the Rambam! We said that he holds that when one has a doubt about a מצוה דאורייתא then he must fulfill the mitzva [מדרבנן] out of doubt. However no bracha is made because maybe he is not חייב at all. According to the Rambam there is no new, absolute חיוב מדרבן [as we said מתורת ודאי] to fulfill a ספק דאורייתא. If there were - then a bracha would be made on the Bris Milah of an אנדרוגינוס.
I had this problem for the longest time but today - בסייעתא דשמיא - I think I may have found a solution.
The Rambam says that if a person is not sure whether or not he read Shema then not only does he say שמע out of doubt but repeats the brachos as well. How does that dovetail with his opinion that a bracha is not made on the Bris of an אנדרוגינוס? Here also we should read the Shema but skip the [מדרבנן] brachos and save ourselves brachos li-vatala.
The Kesef Mishna was bothered by this and answered in the name of the Rashba that birchos Krias Shema must be read with Shema.
What does THAT mean?
Rav Soloveitchik explained that according to the Rambam there is a special rabbinic decree that birchos Krias Shema are part and parcel of Krias Shema. Thus, we must say the brachos together with Shema. This is in contrast to all other mitzvos where the brachos are separate from the actual mitzva. This separation enables us to do the safek mitzva without the bracha. The Raavad argues and holds that the mitzva and bracha are one unit and if you must do the mitzva out of doubt then you also must make a bracha as well.
So their argument about מילת אנדרוגינוס is not whether the mitzva must be done מתורת ספק [Rambam] or מתורת ודאי [Raavad] but as to whether the bracha is one unit with the mitzva or a separate entity. But maybe EVERYBODY holds that the mitza must be done מתורת ודאי.
If everything I said until now is true then we have a strong defense of the Pri Megadim. A woman can be מוציא a טומטום because this טומטום is completely not obligated מדאורייתא [because ספק דאורייתא לקולא] and has a new חיוב מדרבנן which is מתורת ודאי. So both the טומטום and the woman have the same level חיוב מדרבנן and she can thus be מוציא the טומטום.
PLEASE tell me if I am wrong!