People just can't let a good thing alone -- especially if fiddling with it in an attempt to make it better isn't very difficult. The impulse to take something generic and somehow make it one's own is deeply ingrained in the human spirit.

And one of the most obvious modern illustrations of it is what many of us do with cake mixes.

One glance at the supermarket cake-mix shelf makes clear that the makers of these products bend over backwards to offer a range of flavors wide enough to supply almost every taste.

At a typical supermarket there are about 40 kinds of mixes for 2-layer cakes. Eliminating overlap between the three major brands, there remain about 20 different flavors, including 9 or 10 versions of chocolate.

Still, people persist in taking these perfectly satisfactory cake mixes and -- in a search for the moistest, prettiest, tastiest, most interesting cake -- stirring in pudding mixes, gelatin mixes, soft drinks, mayonnaise, sour cream, liqueurs and a host of fruits and vegetables.

Such cake-doctoring isn't a new phenomenon. Even before the wide popularity of cake mixes, "You'll never guess what's in this cake" was often heard at bridge parties more than 50 years ago.

The likes of 7-Up Cake, Sauerkraut Fudge Cake and Chocolate Mayonnaise Cake, all made from scratch, were offered in the expectation of oohs and ahs and expressions of delight over the interesting taste or the delightfully moist texture.

There wasn't quite as much doctoring of made-from-scratch cakes as there is now of cake-mix cakes -- or at least people didn't doctor from-scratch cakes in quite as many different ways as they doctor mixes, for a very good reason: From-scratch recipes aren't necessarily very tolerant of major modifications. Tossing a box of pudding or a tub of sour cream or a can of pureed fruit into a from-scratch cake could easily turn what would have been a perfectly nice cake into a tub of goo.

Manufacturers of cake mixes are very aware of how much latitude their products must allow -- both for mismeasurement (a successful cake mix needs to turn out decently even if the baker mistakenly added too much oil or too few eggs) and for intentional doctoring.

Some of the "chemical" ingredients found on cake mix boxes -- things you don't put into your from-scratch cake -- are there to help ensure that the cake will turn out nicely almost no matter what you do to it, and companies do extensive "tolerance" testing to see that their mixes survive all but the most extreme assaults.

Cake-mix makers also try to make their cakes turn out the way folks want them without requiring the folks to add things to them, which has led to this interesting circumstance:

Following a flood of recipes -- including contest-winners -- that involved adding pudding mix to cake mix to achieve extra moistness, many cake mixes were reformulated to include "pudding" (generally in the form of cornstarch) to produce moister cakes right from the package.

Such "pudding in the mix" cake mixes are now far more common on the shelves than those without pudding. Virtually all the Pillsbury and Betty Crocker mixes are of this pudding-added type, and they say so on the box. But people insist on adding pudding mix to the pudding-added cake mixes.

For a while, many recipes that called for adding pudding mix to cake mix called for using a cake mix that didn't already contain pudding. (Duncan Hines offers a few of those: Scan the ingredients list for the absence of cornstarch.)

Although this warning still is encountered from time to time, product specialists at both Pillsbury and General Mills advised that this shouldn't be a problem.

"In fact," said Pillsbury's Hilary Bakker, "one of our most requested recipes involves adding pudding to one of our [pudding-in-the-mix] mixes."

So. Pleased at the paucity of potential problems, do you find the possibility of preparing practically perfect -- but pleasantly personal -- cakes . . . provocative? But are you hesitant to strike out on your own?

A recent book, "The Cake Mix Doctor," by Anne Byrn (Workman, 454 pages, paperback, $14.95), is an interesting attempt to address this problem. It contains more than 150 recipes for doctored cake mixes.

It is not for the likes of me to decide whether preparing a doctored cake mix using a recipe is, in fact, doctoring a cake mix, or whether it is following a recipe. That's in the same department as whether Certs is a candy mint or a breath mint, or how many angel-food cakes can dance on the head of a toothpick, and we leave it as an exercise for philosophy majors.

If you like this idea and want even more recipes for doctored cake mixes than Byrn's book provides, the best place to look may not be the Internet.

Although, like everything else, doctored-cake-mix recipes can be found scattered around cyberspace, the most concentrated source for doctored cake mixes is cookbooks published by churches, civic organizations and the like.

These are repositories of members' signature dishes -- the ones they trot out for parties -- and many of the desserts are doctored cake mixes. Several of the recipes offered here today are from such cookbooks.