In a recent study, researchers have discovered that birds who live in cities have differences in their DNA when compared to birds who live in the countryside. The populations of great tits in nine popular European cities were examined. Genes involving cognition and various behaviors relating to serotonin were selected and passed down based on the environment they lived in. The behaviors and sleep cycles of the birds living in cities varied from those in the country. To live in a city, birds have to adapt to the light, noise, and air pollution created by these cities. They also need to adapt to living in close proximity to humans. 192 great tits from Malmo, Gothenburg, Madrid, Munich, Paris, Barcelona, Glasgow, Lisbon, and Milan were studied. Blood samples were compared to birds who lived close by in a rural area. Researchers discovered over half a million single-nucleotide polymorphisms. Many genes seemed to be influenced by this city environment. Great tits are found all over Europe and believed to be very similar genetically, but these studies discovered genetic differences based on the location these birds live. Human influence on the behavior of animals has been known, but I find it interesting how rather new modern cities have already influenced the genetic makeup of birds. It would be interesting to see other genetic differences based on location in other animals living in close proximity to humans.