Grab that glutamate
This month's Nature Genetics (subscription required) has a cool short communication by Fabien Burki and Henrik Kaessmann about a gene that is most likely only expressed in the brain, and is only found in humans and apes. This gene, GLUD2, and its more widespread relative, GLUD1, encode proteins which help break down glutamate. Glutamate is an important neurotransmitter in the brain, and can be released in large amounts during intense neural activity. However too much released glutamate can be toxic, and these two genes are important for control of glutamate levels.
The gene GLUD2 has a fascinating natural history. It originated relatively recently in the hominid lineage as a retro-duplication, an event in which retroviral proteins grab host gene products known as mRNA, transcribe them back into DNA, and tuck them back into to the genome in a new location. These retro-duplications create a partial copy of the original host gene, lacking the "control panel" of DNA sequences which are responsible for gene activity and other features of most genes. These copies are called pseudogenes, because most often they are never made into mRNA.
The insertion site of GLUD2 somehow came under the control of elements that allow it to be expressed only in the brain. In addition, selective evolutionary pressure allowed the protein encoded by GLUD2 to accumulate mutations improving functioning in the brain environment relative to the parent gene, for example functioning well at low pH and in the presence of high GTP. The result is that humans and apes have an evolutionarily new enzyme to metabolize glutamate in the brain.
Pseudogenes are very numerous in the human genome, and can be analysed in great detail now that the human genome has been sequenced. All of this copying, shuffling, and refurbishing can give natural selection plenty of differences to act upon, meaning that little stories like that of GLUD2 can be a big part of the evolutionary process.