Math Horizons | 2019
The Phylogenetics of Beer
Abstract
he field of phylogenetics explores evolutionary relationships between species. By analyzing heritable genetic information for species, the biologist constructs a genetic tree having species as leaves and the branch points indicating when previous ancestors diverged. The length of the edges captures a sense of “evolutionary time,” indicating how genetically close the species on one side of the edge are to those on the other. Mathematics is perfectly poised to help build these trees, and the tools of algebra, probability, statistics, combinatorics, geometry, and analysis have provided great advances. Indeed, the past decade has seen an explosion of activity in phylogenetics, involving nearly every field of mathematics. Some wonderful books in this area include the classics by Joseph Felsenstein (Inferring Phylogenies, Sinauer Associates, 2004) and Charles Semple and Mike Steel (Phylogenetics, Oxford University Press, 2003). Today, the prevalence of data has allowed phylogenetics to have a great impact on old frameworks. After about 130 years of status quo, a recent paper in Nature provided a challenge to traditional dinosaur classification. Building a phylogenetic tree from new data, the authors argued an alternative relationship between dinosaurs, one in which the stegosaurus and the tyrannosaurus are closer evolutionary cousins than previously assumed (Matthew Baron, David Norman, Paul Barrett. “A new hypothesis of dinosaur relationships and early dinosaur evolution.” Nature 543 [2017]: 501–506). Although the original intent of phylogenetics was to build evolutionary trees, the technique can be applied more generally to organize and classify items by similarity. It has become an increasingly useful tool for data analysts who want to classify and relate various items given certain measured traits even if there was no evolutionary process that created them. This article is far less ambitious than a re-examination of long-dead dinosaurs. But it is possibly more practical. We focus not on creatures, but rather on craft beer. Beer is more accessible to the masses than is wine, but as Charles Bamforth reasoned, it is arguably as subtle and complex in its nature (Grape vs. Grain: A Historical, Technological, and Social Comparison of Wine and Beer. Cambridge University Press, 2008). Although beer is quite ancient, with recorded history dating back as early as 4000 BC, the modern classification of beer styles began in 1977 with the publication of Michael Jackson’s seminal book The World Guide to Beer (Prentice Hall). This classification includes two main types of beer, ales and lagers, along with numerous substyles including pilsners, stouts, porters, and wheat beer. In this study, we compare and classify beer not based on classical labels, but rather using actual data and phylogenetic techniques. Satyan L. Devadoss, Lia Hebert, and Sophia Raglione