Two Princeton professors, a husband-and-wife team, traveled to the Galápagos Islands every summer for ~40 years to watch evolution happen in real-time. They weren't studying fossils. Rather, they were measuring the beaks of Darwin's finches. And it paid off. Their names are Peter and Rosemary Grant, and I think more people ought to know their story. There is a beautiful book about their work, called "40 Years of Evolution: Darwin’s Finches on Daphne Major Island," but I don't know many people who have a copy. So here's their story, in brief. The Grants first visited the Galápagos in 1973. They chose to camp on a tiny, rugged island called Daphne Major, which is really little more than a volcanic crater with a rim rising 120m above sea level. There are zero trees on this island, and Charles Darwin did not visit it during his voyage on the HMS Beagle (1831-1836). But alas, the Grants sat on this island month after month, year after year. At first, it wasn’t clear exactly what they'd find. They were interested in evolution, but evolution was supposed to be slow; too slow to measure in a single summer, at least. So the Grants went back to this island (and some nearby islands) again and again. They set up camp, captured and tagged finches, and carefully measured (using calipers) the lengths of their beaks, shapes of beaks, and the food they ate. The Grants meticulously recorded data on each bird, generation after generation, in the hopes of seeing something change. Their work began paying off, and massively so, in the 1980s. In 1989, for example, the duo published a paper in The American Naturalist entitled, simply, "Natural Selection in a Population of Darwin's Finches." The study showed (you guessed it!) natural selection in action. By carefully studying finches on another Galápagos island, called Genovesa, the Grants figured out how major weather changes (in this case, a severe drought), majorly shifted which finches were able to reproduce and, therefore, pass on their genes. In the mid-80s, on Genovesa Island, there was an unusually wet year followed by two dry years. Birds with longer beaks mainly fed on cactus flowers and fruit, but those foods disappeared, causing many of these birds to die. Birds with deeper, stronger beaks had an advantage because they could pry insects from bark and cactus pads, foods that were still available. And this had knock-on effects in how these birds reproduced. In one post-drought year, males with deeper beaks were better at attracting mates, probably because they had extra energy from eating more calories. The "deep beak" birds started winning out. But then, in 1993, another paper from the Grants showed the impact of a rare El Niño event. Heavy rains again changed food availability dramatically. Suddenly, finches with smaller beaks had an advantage because the rains came to the islands and softer seeds became plentiful. Evolution reversed directions and, again, all of this was easily measurable. In 2002, the Grants published (arguably) their most significant paper. It is called "Unpredictable Evolution in a 30-Year Study of Darwin's Finches," and it appeared in Science. The paper's central premise is this: By measuring two types of birds on Daphne Major from 1972 until 2001 (the medium ground finch and a cactus finch), the Grants showed how "favored" body sizes and beak traits shifted drastically, and how evolution could occur in animals at time scales that some biologists assumed were infeasible. "Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual," the Grants wrote. In short, the Grants showed—with extremely thorough and convincing data—that evolution wasn't steady or predictable; it jumps around unpredictably, driven by environmental shifts like droughts or heavy rains. The birds on these islands evolved really fast, with their beaks becoming larger or smaller in just a few generations, depending on what food was available. In 2006, the Grants also documented "character displacement," observing how two similar finch species changed their beak sizes to avoid competition. When a larger-beaked species moved onto Daphne Major, the original finches on the island actually evolved smaller beaks within a few years to avoid competing with the newcomers. Peter and Rosemary Grant are now retired from Princeton, and their last visit to Daphne Major was in 2019. But fortunately, their legacy will live on both through their spectacular book (which I really do recommend buying), and their datasets (which are freely available online.) I recommend playing around with the data yourself. The datasets are used in a Caltech Data Science course that I took in 2019, and that's where I first encountered the Grants' work. (See bebi103.caltech.edu.s3-websi…) Thanks for reading!