As a romantic suspense author, I spend a lot of time writing about ladies in peril. And by that token, I have to get them back out of it. So I'm going to use one day a week to talk about self defense and protecting yourself in various ways.
Men and women fight differently. It's a fact. There are numerous, often hotly debated, reasons for this. Some are cultural and sociological - men are conditioned to roughhouse from an early age, whereas women generally only associate fighting with punishment. And then some are physical - like the adrenaline dump.
Men process adrenaline faster. When that first punch hits them, they get a huge dump of epinephrine in their system. It makes them act, even though they've likely lost most of their fine motor control and critical thinking abilities.
Women process adrenaline slower. This means that while they will not necessarily be as immediately inclined to fight back, they will maintain the use of their motor control and critical thinking abilities for longer. Fights happen fast - by the time adrenaline kicks in for women, oftentimes the actual fight is over. This is why you will frequently see women shaking and crying after fights, while men are more often able to hold it together: the men have already gone through the shaky, jittery part of the adrenaline dump in the middle of the fight.
Both reactions have advantages and disadvantages. In a surprise fistfight, a man will usually fare better. But in a surprise firefight, a woman will be able to keep her cool and retain her ability to shoot accurately [Annual reports of police performance in the United States show that while police officers perform relatively well on low-pressure shooting tests (with hit percentages above 90%), they perform substantially worse when firing in the line of duty (with hit percentages around or below 50%; e.g., Morrison and Vila 1998)]. From an evolutionary standpoint it makes perfect sense - a tribe had to protect its women in order to sustain itself; a tribe of one man and several women would be much better off in the long run than a tribe of one woman and several men. The women were able to keep their cool, gather their babies, and get away while the men went fuzzy-headed with rage and fought, leaving the women and children time to escape.
Know your strengths, and train your weaknesses. If you're interested, here are a couple great sources on the subject.
ETA: Hey guys, go look at the comments for this one. Some very interesting, relevant stuff from JW.