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In The Case for Mars, Bob Zubrin suggests that women may be physiologically better-suited to the space environment, given a lesser likelihood of coronary episodes; when spacing walking, heart rates apparently zoom well best 100 beats per minute. Conversely, lower blood iron content means a greater risk of anemia, as I recall. (As I'm sure you trust your readers for medical advice, pass it along!)
If there are already enough women in the program in 2007 that, coincidentally, two might be commanding missions simultaneously, where will we be in 25 years when we do land on Mars? Surely there'll be enough women that the first footprint might be female. It would be fitting.