I have an undergraduate degree in biology, which means I have studied Darwin’s finches more times than I can count. The short version is that Darwin was on a ship that sailed to the Galapagos Islands. While there he observed many different species and variation within and between species. One of the groups that interested him the most was a number of different birds that showed variations in things like their beaks. Birds with different beaks were adapted to eat different types of food. Later researches discovered that different environmental conditions favoured different beak types, meaning that the visible characteristics of a population could fluctuate significantly within decades.
New research indicates that this variation may not be a result of actual changes to the DNA of the birds but rather changes in how the DNA is methylated (McNew et al, 2017). DNA methylation is the addition of methyl groups (some carbon and hydrogen) to the DNA molecule. It is essential to how our DNA works, but it can also change how it works. This is the realm of epigenetics which examines things that affect how DNA is expressed rather than changes in the code itself.
McNew et al compared urban and rural populations of the same two species and found significant differences in how the DNA was methylated. They hypothesize that these differences account for the main differences between the urban and rural populations.
There is still work to be done. They only compared certain elements of the DNA sequence, so they can’t entirely rule out the DNA itself as the cause for differences. They also don’t actually know what the effects of the epigenetic differences are, so they can’t say that they are responsible for the differences either. However, it is an interesting look at an old topic that has implications for undergraduate biology classes, as well as for the study of epigenetics in all populations.
Sabrina M. McNew, Daniel Beck, Ingrid Sadler-Riggleman, Sarah A. Knutie, Jennifer A. H. Koop, Dale H. Clayton, Michael K. Skinner. (2017). Epigenetic variation between urban and rural populations of Darwin’s finches. BMC Evolutionary Biology, 17(1), 1-14. DOI: 10.1186/s12862-017-1025-9