Study traces the evolution of the human brain

Women can take comfort from the discovery that it is the quality of connections in the brain, not the overall size, that really matters.

	It is increase in the number of synapses in larger animals that allows more sophisticated thought

For decades, men have gloated over how they have bigger brains, and thus must be smarter, a simple side effect of how they tend to have bigger bodies.

Now female intuition that this is simplistic, misleading, even just plain wrong, has been found by new research on the evolutionary origins of the brain and how it evolved into the remarkably complex structure found in humans.

The research in the journal Nature Neuroscience by Professor Seth Grant, Head of the Genes to Cognition Programme at the Wellcome Trust Sanger Institute, suggests that it is not size alone that gives more brain power.

Instead, he found that, during evolution, increasingly sophisticated molecular processing of nerve impulses - notably by providing more connections in the brain - allowed development of animals with more complex behaviours.

"We are one step closer to understanding the logic behind the complexity of human brains," he said.

Current thinking suggests that the protein components of nerve connections - called synapses - are similar in most animals from humble worms to humans and that it is increase in the number of synapses in larger animals that allows more sophisticated thought.

But this has been challenged by the study done at the Sanger Institute, with colleagues at Edinburgh and Keele Universities.

"Our simple view that 'more nerves' is sufficient to explain 'more brain power' is simply not supported by our study," explained Professor Grant.

"Although many studies have looked at the number of synapses, none has looked at the molecular composition of synapses. We found dramatic differences in the numbers of proteins in the synapses between different species.

"We studied around 600 proteins that are found in mammalian synapses and were surprised to find that only 50 percent of these are also found in invertebrate (creatures without a backbone, such as insects) synapses, and about 25 percent are in single-cell animals, which obviously don't have a brain.

"The number and complexity of proteins in the synapse first exploded when multicellular animals emerged, some billion years ago. A second wave occurred with the appearance of vertebrates, perhaps 500 million years ago"

Since the evolution of complex, 'big' synapses occurred before the emergence of large brains, it may be that these molecular evolutionary events were necessary to allow evolution of the human brain..

"The molecular evolution of the synapse is like the evolution of computer chips - the increasing complexity has given them more power and those animals with the most powerful chips can do the most," continues Professor Grant.

Synapses are the junctions between nerves where electrical signals from one cell are transferred through a series of biochemical switches to the next.

However, synapses are not simply soldered joints, but mini-processors that give the nervous systems the property of learning and memory. Remarkably, the study shows that the origins of thinking like in feeling: some of the proteins involved in synapse signalling and learning and memory are found in yeast, where they act to respond to signals from their environment, such as stress due to limited food or temperature change.

"It is amazing how a process of Darwinian evolution by tinkering and improvement has generated, from a collection of sensory proteins in yeast, the complex synapse of mammals associated with learning and cognition," said Dr Richard Emes, Lecturer in Bioinformatics at Keele University, and joint first author on the paper.

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