A paper appearing today in PLoS Biology suggests that new genes play a bigger role than previously thought in explaining the complex functions of the human brain. Researchers at the University of Chicago Department of Ecology and Evolution reached this conclusion by comparing the age of genes with transcription data from humans and mice. Where are new genes most often expressed? In humans, it’s in the brain. Even more interestingly, it’s in the developing brain of the fetus and the infant.
One of the researchers, Yong E. Zhang, was motivated to ask these questions because he accompanied his pregnant wife to prenatal ultrasound appointment, according to a press release issued by the University of Chicago Medical Center. According to Zhang, “Newer genes are found in newer parts of the human brain.” The press release also quotes co-author Patrick Long: “What’s really surprising is that the evolutionary newest genes on the block act early….The primate-specific genes act before birth, even when a human embryo doesn’t look very different from a mouse embryo. But the actual differences are laid out early,” Long explained.
In the language of the PLoS Biology paper, the authors “observed an unexpected accelerated origination of new genes which are upregulated in the early developmental stages (fetal and infant) of human brains relative to mouse.” In other words, compared to all the genes in the human genome, younger genes are significantly more involved in those parts of the brain that make us distinctly human. More than that, these genes play a greater than expected role in prenatal and infant development, the very period in which the brains of humans develop so rapidly compared to the brains of other species.
How did these new genes arise? By all the various means by which new genes arise—by various processes of duplication and by de novo origination. Rather remarkably, the authors make this observation: “…young genes created by all major gene origination mechanisms tend to be upregulated in [the] fetal brain. Such generality suggests that a systematic force instead of a mutational bias associate with a specific origination mechanism contributed to the excess of young genes in the fetal brain.”
What “systematic force”? Clearly, the authors are not speculating about anything more than a statistical correlation. But their work will give rise to new questions for research. What role do these young genes actually play in the developing brain? What role did natural selection play in the evolution of these genes? Does this surprising correlation shed any light at all on our rapid rise as a species and the stunning complexity of the human brain?
The paper, "Accelerated Recruitment of New Brain Development Genes into the Human Genome," is published in the October 18 issue of PLoS Biology [10.1371/journal.pbio.1001179].