It’s not what we have, but what we don’t have. A team of researchers from the US has found that the human genome lacks some key aspects compared with the genomes of other primates. According to their new study, this could have played an equally important role in the development of human beings. In other words, what we lost from our genome may be just as important as the genetic additions that occurred during our evolutionary history.

The study fills a big gap in what’s known about changes to the human genome. Over time, scientists have been able to identify unique additions to the human genome, including a gene that played a crucial role in the development of human speech. However, much less attention has been given to what’s absent from the genome.

“Often we think new biological functions must require new pieces of DNA, but this work shows us that deleting genetic code can result in profound consequences for traits make us unique as a species,” Steven Reilly, an assistant professor of genetics at Yale School of Medicine and senior author of the paper, said in a statement.

Looking into the human genome

It’s been two decades since the initial rough draft of the human genome, consisting of three billion genetic letters of DNA coiled up inside the majority of our cells, was compiled by scientists. Despite this lengthy period, researchers are still facing challenges in deciphering it. Now, a new research endeavor aims to tackle some of these issues.

Researchers at Yale and the Broad Institute of MIT and Harvard looked at primate DNA and found the loss of about 10,000 bits of genetic information over our evolutionary history differentiates humans from chimpanzees – our closest primate relative. Some of these bits relate to genes involved in neuronal and cognitive functions, the team said.

However, certain genetic deletions didn’t interfere with human biology, the researchers said. Instead, they produced novel genetic codes that removed elements that typically suppress gene expression. Reilly compares this process to removing three characters — “n’t” — from the word “isn’t” to create a new word, “is.”

The researchers used a technology known as Massively Parallel Reporter Assays. It enables the screening and measurement of the function of genetic changes across various species. According to Reilly, this tool can help in identifying the multiple molecular small components that contribute to our distinctiveness as a species.

The study was one of several published by the Zoonomia Project, a research partnership that catalogs the diversity in genomes by comparing DNA sequences from 240 species of mammals that exist today. One of the papers, for example, focused on how we can use DNA information to predict which species are more likely to face extinction.

Altogether, the database from the Zoonomia Project is actually a starting point to better understand what makes us human. “We are identifying segments unchanged across all species, as well as segments changed in just a few, and discovering both the genomic basis of traits essential for all animals,” the researchers wrote on the project’s website.

The study was published in the journal Science.