A new study supports a 30-year-old theory that states: the main difference between humans and chimpanzees may be found in the way genes are expressed * Scientists publish corrections to the theory of evolution; The study will be published soon
How can humans and chimpanzees, who share 99% of the same genes, be so different?
Scientists in the United States and Australia say that changes in gene expression, and not just the genes themselves, are a large part of what differentiates humans from their closest relatives.
Expression of genes is the process in which genes are 'turned on' and 'turned off'. Not all of the estimated 30,000 genes present in humans are active at the same time in every cell.
The scientists, from Yale University and the University of Chicago in the United States, and their colleagues from the "Hall" Institute in Australia, believe that gene expression is a large part of what distinguishes chimpanzees from humans. They tested gene expression in humans, chimpanzees, orangutans and rhesus monkeys. To do this, they used a new gene array method to compare the expression level of 1,056 genes in the four species. When they looked at gene expression, they found fairly small changes in the 65 million years of evolution of macaques, orangutans and chimpanzees.
But rapid changes have subsequently occurred in specific groups of genes known as 'transcription factors', which control the expression of other genes, since humans 'split' from their ape ancestors over the past 5 million years. The rapid evolution of the transcription factors appeared only in humans, they wrote.
The study, published in the "Nature" newspaper, supports a 30-year-old theory by scientists Marie Claire-King and Ellen Wilson, which states that the main difference between humans and chimpanzees may be found in the way genes are expressed. Until the mapping of the human genome and the development of gene array technology allow large-scale analysis of gene expression, the theory cannot yet be tested.
The researchers used liver tissue samples from five living males of the four species in the study, and found that 60% of the genes had consistent expression levels in humans and higher mammals. But genes for transcription factors were more likely to change their expression patterns than the genes they regulate.
Especially in the human lineage, transcription factors change, or evolve within expressions, at a faster rate than in other lineages, especially compared to chimpanzees.
The researchers do not know what caused the change in gene expression in humans, but they suspect that it may be due to changes in the environment, the discovery of fire and a preference for cooked food.
They plan to use other types of tissue to study larger arrays of genes in future studies.
