Researchers at University College London and University of Cambridge say mammals with large brains may have evolved their larger brains due to the long-term investment of maternal care.
The British researchers focused on analyzing brain sizes of 197 marsupial mammals, such as kangaroos and possums, and 457 placental mammals, such as cats, dogs, and horses. They found marsupial brains to be of equal or even larger size than those of placental mammals.
A competing theory attributes larger brain size in mammals to metabolism. Physorg.org reported there has been such a focus on metabolic rate and brain size, that the role of maternal care has been overlooked. Dr. Anajali Goswami said, “If we take primates out of the equation, we discover that marsupials, despite having much lower metabolic rates, have similarly sized brains, or sometimes even bigger brains, than their placental mammal counterparts. So clearly, evolving big brains is not just about having a high metabolism. Instead, it seems maternal care is the most consistent factor driving the development of big brains across all mammals.” (Source: University College London)
Marsupial brains experience the most growth after birth, and placental brains during gestation. For marsupials, the British research may show the long lactation and period of maternal care is a critical phase of brain development.
Primate brains grow during gestation and after birth from maternal care. Research about metabolic rate in orangutans appears to be in alignment with British marsupial study. Orangutans were found to have a very low metabolic rate, and yet are one of the most intelligent mammals. Research from decades ago used inanimate fake mother figures with baby rhesus monkeys. It found the baby monkeys chose a non-feeding fake mother made from terry cloth over a wire fake mother which provided food. This research also found without the comforting aspect of a soft mother presence the babies experienced high stress, which interfered with their development.