Recipes for peanut butter cookies always say to do something peculiar to them, prior to baking: use a fork to create grid-like cross-hatches. Where did this come from? We all do this, but we're not entirely clear why we do (or at least I wasn't). This got me thinking whether this could be an example of cultural diffusion, where we could see how the cross-hatching spread from one baker to the next. Just as there is biological change, so too does our culture—extremely broadly construed—alter over time, with various aspects spreading and changing.
Both utilitarian and ornamental cultural features can be subject to evolution. So, is the cross-hatching of peanut butter cookies adaptive, or is it something that has simply spread due to other reasons (such as aesthetic ones)?
We have the answer from Wikipedia:
The early peanut butter cookies were rolled thin and cut into shapes. They were also dropped and made into balls. They did not have fork marks. The first reference to the famous criss-cross marks created with fork tines was published in the Schenectady Gazette on July 1, 1932. The Peanut Butter Cookies recipe said "Shape into balls and after placing them on the cookie sheet, press each one down with a fork, first one way and then the other, so they look like squares on waffles." Pillsbury, one of the large flour producers, popularized the use of the fork in the 1930s. The Peanut Butter Balls recipe in the 1933 edition of Pillsbury's Balanced Recipes instructed the cook to press the cookies using fork tines. The 1932 or 1933 recipes do not explain why this advice is given, though: peanut butter cookie dough is dense, and without being pressed, it will not cook evenly. Using a fork to press the dough is a convenience; bakers can also use a cookie shovel.
So it looks like that there are utilitarian reasons for the cross-hatching—to allow for even cooking—but it might have been passed along for nearly a hundred years for primarily aesthetic reasons, where the cross-hatching is more to identify the cookies as peanut butter ones, rather than to cook them well.
But can we see how the cross-hatching practice spread? Alas, I can't find data on this (if you have any insights on this, let me know in the comments!). But we can look at cultural diffusion in another case, specifically one of my favorite cases of this in a non-human "society": a celebrated example of how the ability of birds to open milk bottles spread throughout the United Kingdom during the first half of the Twentieth Century.
Here is Brian Switek with more on these birds and imitation:
Thus there was something of a cultural transmission, the birds that opened these bottles to get at the cream each having to learn the behavior on their own but often after being giving a “clue” by watching another bird do it first. Some could have very well figured out how to open the bottles without observing the other birds (Lefebvre, 1995 suggesting a second site for this behavioral innovation and the cultural transmission of it), but the speed and spread of the behavior shows that there was quick transmission of this behavior based upon watching an ever-growing body of modelers.
Here's a map from a paper about this behavior's spread, which demonstrates that it spread quite quickly:
Now, if only the birds had cookbooks, to spread their practices even faster.
Thanks to Debra for the inspiration for this post!
Top image:Denise Krebs/Flickr/CC
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