The continuing process of evolution can be measured in the skulls of small mammals. University of Minnesota biologist Emilie C. Snell-Rood
suggests that the brains of creatures like mice and bats have grown bigger as we humans have changed the landscapes where they live.
Measuring the dimensions of dozens of skulls collected over a century and kept at the school's Museum of Natural History, Snell-Rood and her student Naomi Wick estimated brain size in 10 species. They found that in white-footed mice and meadow voles, brains of animals from urban areas were about 6 percent larger than those of animals collected from farms. Some species of shrews and bats from rural areas also showed an increase in their brain cases.
Writing in Proceedings of the Royal Society B, Snell-Rood theorizes that the brains of all six species have gotten bigger because humans have radically changed Minnesota. Cities and farms in the state have replaced forests and prairies. In this disrupted environment, animals that were better at learning new things were more likely to survive and reproduce.
While other evolutionary biologists will need to test her hypothesis, if she is correct, skulls from museum collections in other heavily developed regions of the world will show a similar trend.