According to a new study, young genes that appeared after the primate branch split off from other mammal species are more likely to be expressed in the developing human brain. The correlation, published online on October 18 in the open access journal PLoS Biology, suggests that evolutionarily recent genes may be responsible for constructing the uniquely powerful human brain.
Recent genes have so far been largely ignored by scientists, but senior author Manyuan Long, PhD, Professor of Ecology & Evolution at the University of Chicago says:
"We found that there is a correlation between new gene origination and the evolution of the brain. There are some 50 to 60 human-specific genes in the frontal cortex of the brain, the part that makes humans diverge with other non-human primates."
Since ancient history scientists have been puzzled by the question how the complex and unique evolution of the human brain separates humans from their primate ancestors. Scientists have turned to genetics to answer questions about our primate relatives and other species since the completion of The Human Genome Project and the increasing availability of genome sequences. Based on these studies, many scientists developed the hypothesis that the spectacular difference of the human brain compared to other species is due to differential regulation of conserved genes shared across species, instead of the arrival of new, species-specific protein-encoding genes.
Long's laboratory however discovered in a 2010 study that the younger, species-specific genes might prove just as significant to the development of an organism, as older, conserved genes.
For the new study lead author Yong Zhang, PhD. and his team merged a database of gene age with transcription data from humans and mice to observe when and where young genes are expressed for each species.
Their findings revealed that the percentage of young genes being expressed in the brain was higher in primate-specific young genes compared with mouse-specific young genes. The researchers also discovered that there was a higher potential for human-specific young genes appearing in fetal brains during the organ's development and also in elaborated brain structures unique in primates, such as the neocortex and prefrontal cortex.
The researchers point out that their discovery is only based on a correlation between the appearance of young, human-specific genes and the evolutionary appearance of advanced brain structures. Future research will assess the function of these genes and the impact they may have had in structuring the unique human brain.
One feature that raises the scientists' curiosity is that many of the new genes seem to code for unique proteins instead of just tweaking the regulation of older, conserved proteins.
"Traditionally, people don't believe that a new protein or new gene can play any role in an important process. Most people only pay attention to the regulation of genes. But out of a total of about 1,300 new genes, only 13 percent were involved in new regulation. The rest, some 1,100 genes, are new genes that bring a whole new type of function."
Written by Petra Rattue