increases the life span of these species.For example, the killer whale has one of the longest pregnancies at 15 months and breast-feeds offspring for another 18 months. Their brains can reach over 300 cubic inches (5,000 cubic centimeters), or about the size of a mini-keg of beer. This extended period also leaves more time for learning and play."The link is all to do with the cost of growing a large brain, and not so much with the benefit of having a large brain," Barton said. "Chimps and other great apes have pretty protracted periods of development and pretty large brains.