Geneticists Aim to Unravel Where Chimp and Human Brains Diverge

Nov 13, 2006

Six million years ago, chimpanzees and humans diverged from a common ancestor and evolved into unique species. Now UCLA scientists have identified a new way to pinpoint the genes that separate us from our closest living relative – and make us uniquely human. The Proceedings of the National Academy of Sciences reports the study in its Nov. 13 online edition.

“We share more than 95 percent of our genetic blueprint with chimps,” explained Dr. Daniel Geschwind, principal investigator and Gordon and Virginia MacDonald Distinguished Professor of Human Genetics at the David Geffen School of Medicine. “What sets us apart from chimps are our brains: homo sapiens means ‘the knowing man.’

“During evolution, changes in some genes altered how the human brain functions,” he added. “Our research has identified an entirely new way to identify those genes in the small portion of our DNA that differs from the chimpanzee’s.”

By evaluating the correlated activity of thousands of genes, the UCLA team identified not just individual genes, but entire networks of interconnected genes whose expression patterns within the brains of humans varied from those in the chimpanzee.

“Genes don’t operate in isolation – each functions within a system of related genes,” said first author Michael Oldham, UCLA genetics researcher. “If we examined each gene individually, it would be similar to reading every fifth word in a paragraph – you don’t get to see how each word relates to the other. So instead we used a systems biology approach to study each gene within its context.”

The scientists identified networks of genes that correspond to specific brain regions. When they compared these networks between humans and chimps, they found that the gene networks differed the most widely in the cerebral cortex -- the brain’s most highly evolved region, which is three times larger in humans than chimps.

Secondly, the researchers discovered that many of the genes that play a central role in cerebral cortex networks in humans, but not in the chimpanzee, also show significant changes at the DNA level.

“When we see alterations in a gene network that correspond to functional changes in the genome, it implies that these differences are very meaningful,” said Oldham. “This finding supports the theory that variations in the DNA sequence contributed to human evolution.”

Relying on a new analytical approach developed by corresponding author Steve Horvath, UCLA associate professor of human genetics and biostatistics, the UCLA team used data from DNA microarrays – vast collections of tiny DNA spots -- to map the activity of virtually every gene in the genome simultaneously. By comparing gene activity in different areas of the brain, the team identified gene networks that correlated to specific brain regions. Then they compared the strength of these correlations between humans and chimps.

Many of the human-specific gene networks identified by the scientists related to learning, brain cell activity and energy metabolism.

“If you view the brain as the body’s engine, our findings suggest that the human brain fires like a 12-cylinder engine, while the chimp brain operates more like a 6-cylinder,” explained Geschwind. “It’s possible that our genes adapted to allow our brains to increase in size, operate at different speeds, metabolize energy faster and enhance connections between brain cells across different brain regions.”

Future UCLA studies will focus on linking the expression of evolutionary genes to specific regions of the brain, such as those that regulate language, speech and other uniquely human abilities.

Source: University of California, Los Angeles

Explore further: Salmon forced to 'sprint' less likely to survive migration

add to favorites email to friend print save as pdf

Related Stories

Sequencing the genome of salamanders

9 hours ago

University of Kentucky biologist Randal Voss is sequencing the genome of salamanders. Though we share many of the same genes, the salamander genome is massive compared to our own, about 10 times as large.

Histones and the mystery of cell proliferation

Aug 19, 2014

Before cells divide, they create so much genetic material that it must be wound onto spools before the two new cells can split apart. These spools are actually proteins called histones, and they must multiply ...

Bioengineers create functional 3-D brain-like tissue

Aug 11, 2014

Bioengineers have created three-dimensional brain-like tissue that functions like and has structural features similar to tissue in the rat brain and that can be kept alive in the lab for more than two months.

Recommended for you

Orb-weaving spiders living in urban areas may be larger

4 hours ago

A common orb-weaving spider may grow larger and have an increased ability to reproduce when living in urban areas, according to a study published August 20, 2014 in the open-access journal PLOS ONE by Eli ...

User comments : 0