Human and Ape Evolution: Why Our Faces Are Different

Ever wonder why humans don't look more like apes, our closest relatives? Well, Stanford researchers recently examined the gene expression behind facial development in order to better understand how two species with common ancestors could evolve so differently from one another.

"We are trying to understand the regulatory changes in our DNA that occurred during recent evolution and make us different from the great apes," Joanna Wysocka, an associate professor at Stanford University, said in a news release. "In particular, we are interested in craniofacial structures, which have undergone a number of adaptations in head shape, eye placement and facial structure that allow us to house larger brains, walk upright and even use our larynx for complex speech."

According to the researchers, different levels of proteins that control facial development, jaw and nose length, and skin pigmentation are expressed differently in chimps and humans.

The team of researchers studied gene-expression by mimicking steps of early primate development in their lab. They dubbed this "cellular anthropology," and focused on enhancer regions of DNA that control gene expression.

In order to zero in on the morphological differences between the two species, by looking at the genes of both, the scientists examined what are called cranial neural crest cells. "These cells are unique," Sara Prescott, the lead author and a Stanford graduate student, said in a statement. "If we want to understand what makes human and chimp faces different, we have to look to the source -- to the cell types responsible for making these early patterning decisions. If we were to look later in development or in adult tissues, we would see differences between the species but they will tell us little about how those differences were created during embryogenesis. But accessing early cell types like neural crest cells can be quite difficult, especially when studying primates."

Wysocka explained in the release that, while many of the regulatory elements found in chimps and humans are the same, there are some differences. She said 1,000 species-biased enhancer regions were found. Some of these regions are more active in one species than the other, and thus cause facial variation.

Their findings were recently published in Cell.

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