When mammals colonised the sea, the whales quickly became successful. With an increasingly complex and large brain, the toothed whales were able to achieve the heights of the sociable, playful and even friendly animal we know as the dolphin.

Sperm whales, meanwhile, have the largest brain in absolute terms, along with a highly-folded and enlarged cortex, an increase in synapse numbers and many other parallels with the advanced terrestrial mammals-primates.

Sperm whale; Credit: © Shutterstock

This sperm whale off Sri Lanka shows some of the anatomy for diving deep in search of giant squid, plus the huge head to contain that largest of brains. Humans have mused for generations on how that obvious intelligence is used. Now we are getting closer to understanding what makes whales tick-and-talk and sing!

Large brains of course are a mammal speciality. See the rodent, elephant or carnivore head and wonder at the thinking ability. The genes that modify and develop energy pathways and their metabolic requirements have also modified the mammal body plan to provide a physiology that richly supports the brain and nervous system.

The bottlenose dolphin, Tursiops truncates, has a completed genome, as have many of the prominent mammals, even including platypus and elephant. And the closest land relative, the cow (now in the order Cetartiodactyla, made up of cetaceans and artiodactyls) was also used by this research as one of the nine comparisons in terms of its gene sequences. The result is a baseline for whale genome investigations in the future.

One of the most interesting dolphin features is the selection for genes expressed in the cells' mitochondria, compared to other mammals. Obvious links with genes that have possible uses for deep diving and fat storage are understandable. What this does is release information about how we developed among the primates, because the evolution is strikingly similar. Even the unique gene changes for a deep sea life are valuable to the understanding we need about how animals survive such extremes.

The molecular landscape of brain evolution and cognition has been uncovered by Michael R. McGowen, Lawrence I. Grossman and Derek E. Wildman in the Proceedings of the Royal Society B: Biological Sciences today. They carried out their research in the Detroit Center for Molecular Medicine and Evolution