This is a fascinating article about bug genitalia!
http://io9.com/5287491/female-bugs-evolved-to-prevent-rape
It talks about female bugs forming essentially armored pre-genitals so that it must happen on their terms, and then talks about an evolutionary arms race amongst the male and female duck population, which I had no idea about. :)
I know this is a little wacky, but if you could make one physical change to human genitalia, what would it be and why?
All comments about bigger penii will be met with an eye-roll. ;) You guys know who you are.

Prehensile Penis. “Hey there! Guess what Mr Wiggles is going to try today!?”
Another pair of arms (or two pair). So I can dedicate one arm to propping me up into the perfect position to use the other three on my partner. I’ve considered this one for a while.
For example: I want one hand to pull hair, one to diddle bits, one to touch and caress elsewhere.. all while I look into my partner’s eyes.
Genius! Do you think that could be evolutionarily maintained?
Sure. Might require some extreme modification to the torso to accommodate the extra muscles and joints.. but I don’t see why not. :-)
If nothing else.. sales of under-arm deodorant would jump.
Easier to just borrow additional people…
Perhaps.. but I don’t always have a spare house boy/girl/servent/slave/third person handy all the time (budget cuts).
:-P
A tongue-like organ just above cervix that could occlude the opening to the uterus with conscious manipulation to prevent or allow conception… AND add another awesome feature to vaginal intercourse!
(I haven’t pondered this extensively AT ALL.)
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Most importantly, do we know any geneticists who could make this happen?
Good question!
Science: It is now 2009. Why don’t I have a jetpack, an unlimited clean energy source, and a vagina equipped with its own tongue yet? I feel like you’ve betrayed me.
OMG, This is *WAY* more fun than the “ability to seal off the pathway to pregnancy much the same way one holds back urine”…
The ability to lay eggs/pods would be nice. None of that nasty-painful and life threatening birthing….
‘nad pads. For added protection.
I’m kind of with Wanda Sykes on this one: detachable vagina.
Oh, my – it would be so nice if you could just take it out to clean it, hang it up to dry, and put it back when you wanted to play!
And silly me was just thinking “the ability to burn more calories and/or obtain aerobic exercise while sitting on my ass in front of the computer and/or television”