More than 150 ‘made-from-scratch’ genes are in the human genome. 2 are totally unique to us.

Humans and chimpanzees split from a common ancestor roughly 6 million years ago, when we set off down separate branches on the evolutionary tree of life. Humans continued to birth completely new genes after that split, some of which arose from regions of the genome long thought to be “junk,” a new study highlights.

In the new research, which was published Tuesday (Dec. 20) in the journal Cell Reports (opens in new tab), scientists scoured the human genome for evidence of brand-new genes being “born.” Specifically, they looked for so-called de novo genes that don’t arise through the usual process, in which genes pick up letter changes, or mutations, as cells make copies of their DNA. This modified DNA gives rise to different versions of the proteins than was made from the original version of the gene.