It’s technically possible for everyone, barring some specific quirk or injury, but men generally find it easier to only shit. I looked it up a while ago and the research was American, so I do wonder if it’s because American men tend to pee standing up and they therefore have a bigger mental barrier between #1 and #2.

I’d like to see the study repeated with men who sit to pee or women who stand (it’s possible and not inherently more difficult than for men, but clothing and culture make it a lot less common than the other way around), because I suspect that the mental barrier is the key here.

I suspect there’s a difference because of other culture-related urination urges. I grew up doing a lot of swimming in lakes, and I was never really discouraged from peeing in the lake, as long as I wasn’t right next to someone (probably pretty gross for some people, but I honestly can’t bring myself to find it very gross). That’s my main experience with rapid, immersive temperature changes, and I still feel an almost overwhelming urge to pee when getting into or out of the shower or any body of water. I can pee immediately before getting into the shower, but that doesn’t make a difference. Infants have the temperature response too, which is why you need to be careful changing a diaper in the cold, lest you get peed on. It can be trained out of you though: a friend of mine grew up swimming competitively and had a lot of experience jumping into and out of pools, where she was discouraged from peeing (thankfully). She no longer feels any temperature related urge to pee that she notices.