I'm in my late 40s. I've noticed many of my friends reconnecting with and marrying people they knew years ago -- sometimes friends, sometimes exes. Is everybody just desperate, or is dating all about timing?

--Wondering

In your early 20s, you know what's vitally important in a partner: that he doesn't have "weird nostrils" or wear a belt buckle with his own name on it.

Then you do some living and maybe get shredded by a relationship or two, and your preferences change. In short, context matters. Context is simply your personal circumstances, and it includes factors like your own mate value, the man-woman ratio where you are (or the availability of same-sex partners if you're gay), and whether you're in a hurry to have a baby before your ovaries retire to a cabin.

It turns out that when looking for partners, we have a budget. It works like it does at the supermarket. You can buy the finest steak and lobster and then starve for the rest of the month, or you can shop more in the Top Ramen and lunchmeat arena and keep yourself consistently fed.

Evolutionary psychologist Norman Li applied this budgetary approach in researching partner preferences. Prior research had poor methodology, simply asking, "Hey, what do you want in a partner?" Well, if somebody asks you that -- sky's the limit! -- what's your answer? "Um, is Chris Hemsworth available? How 'bout Liam?" But when you're constrained, you have to make tradeoffs. You have to "buy" the important qualities first -- "necessities" versus "luxuries," as Li put it. When research participants were most constrained, intelligence and kindness were major priorities for both sexes. When budgets expanded, there was more "spending" in other areas, like creativity.

This might explain why people in their 40s suddenly see something in people they tossed aside years ago or maybe just never thought of as partner material. Basically, at a certain point, many people give up on finding the exact right person and look for a right enough person. For some former sticklers, there comes a point when they're all, "I'm game!" if a guy's address isn't WHX134 (his car's license plate) and he doesn't have multiple wives (two or three of whom he's still married to).

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.