New theory for evolution of brain power

Monday June 9 2008

“Human intelligence has little to do with having a big brain”, the_ Daily Mail_ suggested today. The newspaper report is based on a study that compared human brains with the brains of other species. The study found that “mammals have a higher percentage of proteins” in the regions where nerves connect to each other, called synapses. The researchers found that of the 600 proteins found in mammalian synapses, half were found in invertebrates, and only a quarter in single-celled organisms, which don’t have nerves.

The newspaper quoted the lead researcher as saying, “This work leads to a new and simple model for understanding the origins and diversity of brains and behaviour in all species. We are one step closer to understanding the logic behind the complexity of human brains.”

This complex study contributes to knowledge about the differences in one important group of proteins between the species. This study did not compare the relative contributions of differences in these proteins and brain size to intelligence in humans or any other species, therefore it is not possible to draw any conclusions about their relative importance. The brain is hugely complex, and there will be many internal and external factors contributing to differences in behaviour and learning both between and within species.

Where did the story come from?

Dr Richard Emes and colleagues from Keele University, Edinburgh University, the Wellcome Trust Sanger Institute, and the Okinawa Institute of Science and Technology carried out the research. The study was funded by Wellcome Trust, the Medical Research Council, Edinburgh University, GlaxoSmithKline, the e-Science Institute, and the European Molecular Biology Organisation. The study was published in the peer-reviewed medical journal: Nature Neuroscience.

What kind of scientific study was this?

In this computer and laboratory-based study, the researchers looked at whether differences between synapses in different species, ranging from single celled organisms to humans, might give clues to how the synapses evolved and why different species have different levels of behavioural complexity. They say that despite being “fundamentally involved in neural information processing”, existing discussions of how the brain and behaviour evolved typically do not take into account “the possibility of synaptic molecular evolution”.

To do this, the researchers looked at the proteins that are located in a specific part of the synapse, called the postsynaptic region, in the different species.

To begin with, the researchers took the sequences of the genes which contained the blueprints for 651 proteins found in the postsynaptic regions of mice. They then used computers to find similar sequences in the genetic codes of 19 different species. This included very simple species that do not have nervous systems, such as brewer’s yeast (a single-celled organism), and a range of organisms with nervous systems, including invertebrates (such as insects and worms), non-mammalian vertebrates (such as fish), and mammalian vertebrates (including rats, chimpanzees, and humans).

The researchers looked at the function of these proteins in yeast. They then looked at which proteins were found in the postsynaptic regions of fruit flies, and compared this with the mice. Finally, they looked at where in mice’s brains these different proteins were found.

What were the results of the study?

The researchers found genes encoding proteins similar to the mouse postsynaptic proteins in all of the species, even yeast. There were clear differences in the numbers of varieties of these proteins between the yeast, invertebrates and vertebrates. As organisms become more complex, they contain a greater variety of postsynaptic proteins. In yeast, which do not have nerves, these proteins were involved in a range of jobs within the cell, such as making and breaking down proteins, moving substances around the cell, and responding to the environment.

Comparing mouse and fruit fly postsynaptic proteins showed that the mouse had a more complex range of postsynaptic proteins. Different regions of the mouse’s brains had different combinations and levels of these proteins. This suggests that they may be responsible for some of the different functions in these different areas of the brain.

What interpretations did the researchers draw from these results?

The researchers say that their findings suggest that the basic proteins that make up the synapse have evolved over time to become more complex, and this has contributed to differences in cognitive abilities between different species and to the adaptation of different regions of the brain for different functions.

What does the NHS Knowledge Service make of this study?

This study contributes to knowledge about the differences in one group of proteins between the species. The brain is hugely complex, and there will be many differences between species that contribute to differences in their cognitive abilities and behaviour.

Sir Muir adds...

Everything in life is to do with relationships; "only connect", as E.M. Forster said.

Analysis by Bazian
Edited by NHS Choices