There is a reson why the gingko tree, the armadillo and the horsecrab haven't changed since prehistoric times -- you don't fool around with a perfectly good thing.

So why fool with a time-tested custard pumpkin pie? Because if you're lucky, you might hit a compatible combination of pumpkin and cream cheese, or pumpkin with a crisp pecan topping.

The original pumpkin pie was an invention of necessity. The Indians had the pumpkin but the colonists weren't particularly impressed by the taste. They cut it open and filled it with a few spices. From there they took a pastry crust, well-established in England by the 17th century, and, once supply ships were a little more reliable, added eggs and milk to the pumpkin pulp to make a custard for the crust.

However, it didn't taste that great. Molasses was needed to sweeten the pie (sugar was a luxury food), but it was not readily available. In fact molasses was so scarce in colonial times that cooks used it only for celebrations. It was so important that on several occasions a New England town put off its Thanksgiving feast a week or more waiting for a shipment of molasses from the West Indies.

Today, molasses and pumpkin pie both are easy to find in supermarkets, so we decided to taste some basic quickies before moving on to pumpkin pie variations solicited from readers as part of our "Why Not the Best?" series. Libby's instant pie in a can was fast and cheap: You just add eggs and evaporated milk and pour it into a crust. But the tasters didn't rave. Mrs. Smith's frozen pie took too long to cook and was a bit rubbery. Also, while a pumpkin pie filling made with heavy cream was preferred over one that used evaporated milk, the taste difference wasn't enough to justify the higher cost of cream.

Of the variations we tried: a "health food" pie -- wheat germ and whole wheat pastry crust (like vacuum cleaner dust) with a molasses-and-honey-sweetened custard that tasted too much like it was good for you. We tried a few chiffon pumpkin pies -- too time-consuming to make and too puffy after a large meal. Ricotta cheese and pumpkin was interesting, but too heavy. The pumpkin ice cream pie from Baskin and Robbins ($5.95) was great as ice cream, but didn't taste like pumpkin, and it looked tacky. We tried a rum-and-pumpkin pie that tasted a lot like mud. Then we tried a yogurt-based pie, which was tart and tangy but too unfamiliar.

A farmer-type friend of mine told me pumpkins were not at their best this year, so I took his word for it and used canned pumpkin for all the recipe tests. Since pumpkins almost disappear from markets after Halloween each year, and there is enough to do during Thanksgiving without scraping cooked pumpkin pulp, we decided on the canned pumpkin and prepared crusts.

In total we tested 14 pumpkin pie variations and came up with three recipes that are fantastic, got raves -- even a few swoons. PUMPKIN CREAM CHEESE PIE 1 unbaked pastry shell (9 inches) 1 package (8 ounces) cream cheese, softened 3/4 cup sugar 2 tablespoons flour 1 teaspoon cinnamon 1/4 teaspoon nutmeg 1/4 teaspoon ginger 1 teaspoon grated lemon peel 1 teaspoon grated orange peel 1/4 teaspoon vanilla 3 eggs 1 can (1 pound) pumpkin Sour cream topping (see below)

Heat oven to 350 degrees. In a large mixing bowl, blend cream cheese, sugar and flour. Add remaining ingredients except topping; beat until smooth. Pour into pastry-lined pie pan. Cover edge with a 2- to 3-inch strip of aluminum foil to prevent excessive browning; remove foil last 15 minutes of baking. Bake 50 to 55 minutes or until knife inserted in center of pie comes out clean. Immediately spread top of pie with Sour Cream Topping. Cool. Refrigerae at least 4 hours. Serve well-chilled.

Sour Cream Topping: Blend 3/4 cup sour cream, 1 tablespoon sugar and 1/4 teaspoon vanilla.

-- From "Betty Crocker's Pie and Pastry Cookbook" PUMPKIN PECAN PIE 1 unbaked pastry shell (9 inches) 2 eggs, slightly beaten 1 can (1 pound) pumpkin 3/4 cup sugar 1/2 teaspoon salt 1 teaspoon cinnamon 1/2 teaspoon ginger 1/4 teaspoon cloves 1 2/3 cup light cream or evaporated milk Caramelized Pecan Topping (see below)

Blend together eggs and pumpkin. Stir in sugar, salt, cinnamon, ginger and cloves. Blend in cream. Turn into pie shell. Bake in 400 degree oven 45 to 55 minutes or unitl knife inserted halfway between center and edge of pie comes out clean. Cool completely on rack.

Caramelized Pecan Topping: Combine 3 tablespoons soft butter, 2/3 cup brown sugar and 2/3 cup coarsely chopped pecans or walnuts. Gently drop by spponfuls on oven-cooled pie to cover top. Broil 5 inches below heat until mixture begins to bubble, about 3 minutes. Watch carefully; if cooked too long the top will turn syrupy. Cool on rack.

-- From "Farm Journal's Complete Pie Cookbook" MISS ADELAIDE CAHILL'S PUMPKIN PIE WITH MOLASSES MERINGUE Filling: 1 cup light cream (or whole milk) 3/4 cup sugar (brown or white) 1 1/2 cups canned pumpkin 1/2 teaspoon salt 1/2 teaspoon ginger 1/2 teaspoon cinnamon 1/2 teasoon cloves 1/4 teaspoon vanilla 1 tablespoon molasses 1 egg 2 eggs, separated 1 unbaked pastry shell (9 inches) Meringue: 2 tablespoons molasses 3 tablespoons sugar 2 egg whites (reserved from filling) 1/8 teaspoon cream of tartar Few grains of salt 1/4 cup chopped nuts (walnuts or pecans)

Preheat oven to 450 degrees. Filling: Combine cream, sugar, pumpkin and mix well. Add the salt, spices, vanilla and molasses; mix thoroughly again. Beat the egg and egg yolks and add them to the pumpkin mixture. Pour into pie shell and bake for 20 minutes; reduce heat to 325 degrees and bake for 45 minutes longer, until the filling is firm. Cool slightly.

Meringue: Cook the molasses with 2 tablespoons of the sugar until it reaches 238 on the candy thermometer (the soft ball stage). Cool slightly. Beat the egg whites until frothy and add cream of tartar and salt. Continue beating until peaks form. Add the remaining tablespoon of sugar. Pour the molasses into the egg whites very slowly, in a very thin thread. Now hurry. Spread the meringue over the pumpkin filling so that it overlaps onto the crust a bit. Sprinkle with the nuts and bake at 325 degrees for 15 to 20 minutes. Watch the pie carefully, for the meringue scorches easily.