As biologists and rangers approach the Nez Perce pack's chain-link pen deep in the park's interior, they hear a surprising sound -- a wolf barking from outside.

CNN: Wolves' return to Yellowstone sparks controversy

"In the past 10 to 15 years, there have been many hints from a variety of different disciplines that there was a deep link between entropy production and intelligence, " Dr Wissner-Gross told BBC News.

BBC: Entropy law linked to intelligence, say researchers