I've noticed a trend where people are reluctant to allow their friend groups to mix or cross. I've got probably an above-average number of friends, but the number of friends-of-friends I've met in the last three or four years is in single digits.

I think it's because they're carefully managing their persona in each group and don't want to have to explain the multiple facets of their personality. But I don't really know.

> I think it's because they're carefully managing their persona in each group

This is a great point. If that's the root cause the cratering makes sense, it's (scientifically) known that the most stable relationships exist between two people who have one or a few friends in common but who introduce subsets of friend groups to each other.

Yup, also because if someone starts going nuts in one group, it can easily cross contaminate into another and then you’re in an even bigger mess.

People have fewer friends than they used to.

That has a twofold effect:

- You have fewer friends to recommend

- you don’t want to risk the fallout from a bad recommendation affecting the small group that you do have

That can be sort of easily explained without selfishness/people being jaded.

Anecdotally speaking, I've met all of my friends through school/university/work, and all the friend groups I know of (so mine and my friend's) are basically same sex.

I don't think this is a coincidence. Getting education in tech, there were 1-2 girls in my class, by the time I've graduated it was one. Basically same at work.

So, neither I nor people I know have female friends to introduce others to.

Not sure if the situation is the same for women, but probably somewhat similar.

Also, approaching people is being seen as impolite in more situations these days, so less of that is happening.