We humans sure know how to mess with a landscape. We burn, strip, knock down and dig up what nature has put into place. We build where no buildings should go, we turn wilderness into strip malls, we displace wildlife with housing developments and golf courses. Consequences? Often, we consider those after the fact.
Animals that are naturally behaviorally flexible are sometimes able to survive rapid change; those that can’t move or adapt fast enough aren’t likely to make it. But scientists recently reported that, to cope with the madness, some animals are actually evolving bigger brains. And that means humans aren’t just altering the environment but are a force driving evolution in a new direction.
Previous research showed that having a relatively large brain makes you better equipped to survive in a new location and even to thrive there (with successful breeding). Now, by analysing a collection of mammal skulls at the Bell Museum of Natural History at the University of Minnesota, Emilie Snell-Rood and colleagues have determined that some animals living with human-caused habitat disruption are evolving extra cranial capacity, or more voluminous braincases. Urban environments, their report suggests, are in at least some species selecting for flexible behavior, which comes with increased cognition. And, simply, bigger heads can hold more gray matter, which could translate to the necessary boost in smarts.
“That means humans aren’t just altering the environment but are a force driving evolution in a new direction”
Snell-Rood focused on the skulls of mice, bats, gophers, voles and six other small-mammal species that live in Minnesota. She reports that in two species that live in both rural and urban environments – specifically the white-footed mouse and the meadow vole – the urban animals have brains as much as six percent larger than their country cousins. Interestingly, in shrews and bats it was the rural animals with the bigger brains, and in their case the increase was visible over about a century. This is still presumably due to human activity in those locations, Snell-Rood says, and the extra movement required for them to find food. In addition, animals with higher reproduction tended to have more brain growth over time, in part because with all those extra generations, evolution gets more mutations to work with.
“This is one of the diverse routes animals take to deal with humans,” Snell-Rood says. Not all species would necessarily take this path, of course: animals that already have a certain level of cognition would be “pre-adapted” to cities, so no growth is needed. And other animals might find city life quite familiar. “Consider pigeons and peregrine falcons,” Snell-Rood says. “Living on tall buildings in the city is a lot like living on cliffs in their natural habitat. So they naturally do well in urban environments.”
For a country critter less equipped for changed habitat, though, getting a bigger brain means more options. It can facilitate new, innovative responses to new surroundings – useful for exploiting unfamiliar food sources, learning novel signals for use in a noisy environment, and figuring out who is predator and who is prey. It means a much better chance to survive and breed in a fast-changing world. Interestingly, it appears that it’s most important to have higher cognition during the initial years in a changed environment; after that, craniums may shrink again.
While controlled lab studies are needed to find out more about these correlations, Snell-Rood’s work reminds us that what may seem to be small human actions can have very big consequences indeed.
Evolution
