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writes "As humans change the environment, various species are forced to adapt or perish. Now Eric Jaffe writes that a study by evolutionary researchers Emilie C. Snell-Rood and Naomi Wick of the University of Minnesota has determined that there has been "a significant tendency for urban populations to have larger cranial capacity when controlling for body size." To reach that conclusion, the researchers gathered dozens of skulls from the Bell Museum of Natural History and focused on 10 species of mammals that lived in either rural or urban areas as Minnesota became industrialized in the middle-to-late 19th century. Measuring the skulls allowed Snell-Rood and Wick to estimate cranial capacity, and by extension, brain size. Snell-Rood and Wick note two potential explanations for why the species in cities would have larger skulls than those in the country. One is that only animals with bigger brains were capable of surviving in cities in the first place. A second explanation is that as species lived in cities over a long period, their brains actually became bigger to handle everyday challenges of the urban environment. Finally the growth of urban animals' brain cavities also could be due to nutritional changes in city living or genes. "We can speculate that maybe it has to do with exploring new food sources, [or] some of the challenging spatial navigation that might come through going through your town or house or yard," says Snell-Rood."