The "risks" that males are more likely to take have to do with finding a mate. Challenge the alpha male for females, risking death if you lose. Attempt to acquire lots of wealth, probably with risk involved. From a female's perspective risk usually isn't necessary to acquire a mate.

Evolution has not yet had time to give us genes that say "wearing headphones near autos is dangerous."

Consider two types of runners. One type is out there because they want to run. To them, running is an end in of itself. They concentrate on their running, and headphones would be an unwanted distraction. The other type sees running as a means to an end. Perhaps they want to lose or maintain weight or get in shape. To them, running is work, a boring or unpleasant chore, and headphones provide a desired distraction.

Your warning is falling on deaf ears; habitual headphones give away those who do not listen to anybody.

Sexism is never wrong! You just need a different angle.

Headphoned runners are pre-rejecting suitors—and creeps, I suppose, but women think of all rejectable men as creeps, and actual creeps are undeterred by disinterest.

Male runners are a-courtin', so they keep all their senses ready.

I would suggest it's because people don't understand risk.
America has made (part of) the world safe for puppies and other living things, so they just don't realize that they could be engaging in risky behavior, they've been sheltered from it their whole lives.

Women more than men, because men have to try to find dangerous things to do (often egged on by women) while women are protected by their parents.

You live in some craphole, you expect bad things, you live in some comfortable enclave of happy people, like oh, say Ann Arbor, you have a different view of the world.

I would bet not a lot of women wear headphones if they jog around Detroit.

The riskiness from headphones depends on the volume. At low volume, there's no effect on situational awareness.

Guy on the Internet beat me to it. Headphones are the modern "Do not talk to me" sign.

Meh. However, you should write this up for the NYT as a bogus hand-wringing trend story.

I have noticed the same thing on the ski slopes. One of my female friends always skied listening to her IPod while skiing. To me that is almost suicidal behavior given the need to be aware of other skiers and snowboarders in your vicinity.

Based on casual observation, women are also much more likely to be engaged in cell phone conversations while shopping at the supermarket....which probably does *not* count as risky behavior unless the checkout clerk gets mad at the rudeness and strangles her with a plastic bag....

Actually, even at low volume they decrease awareness for most; it's not just volume drowning out other sounds, it's the distraction: if you're paying attention to the music, you aren't paying attention to traffic/somebody following/whatever, at least not as much as you otherwise would.

I'm guessing a lot of women just have a blanket "Nothing can happen" attitude so they listen and run.

You can't hear cars anymore, so why try? I mean, seriously. That gentle "whoosh" sounds like a bicycle. People on bicycles never warn you. You may as well go eyes only.

Women are more likely to multi-task. This makes sense, evolutionarilly, because of the need to keep an eye out for the kids. Ear too. There may be other reasons.
I've finally after several years managed to make myself resume regular exercise. I used to run but gave it up when I got married because the city we lived in was not conducive to a woman running alone. Since then it's more a matter of "how can I justify this time?" I LIKE running -- and walking -- but I usually have a pile of work in the office or around the house. So, I've started combining research and exercise, by LISTENING to the books as I walk. Yep, I walk with headphones. Though if there is any reason to expect trouble -- unusually high traffice, or even foot traffic -- I free up one of the ears, so I can listen. Is it risky? Probably. On the other hand, not being able to convince myself to exercise will kill me in the long run. So, I take the risk when I must. (And for the record, I walk -- will run when I've lost a little more weight -- in a downtown area with broad sidewalks and stay on the sidewalk. My biggest danger is being run over by a bicyclist.)

I vote with the other two above. Some of these women are filtering out unwanted advances and comments.