It’s also a human-wide innovation. Dougherty noted that despite HYDIN2’s relatively recent origins, it is now found in every living person. That’s especially surprising because it landed in a particularly turbulent part of the genome, which often gets rearranged or outright deleted. It had every chance to be lost, and yet has stood the test of time.

The original HYDIN gene plays roles in many parts of the body, including the brain. “We think that original function has been partitioned,” says Evan Eichler, who led the study. He speculates that the ancestral gene still carries out its usual jobs in other tissues, which is why mutations in HYDIN lead to a rare disease of the lungs and airways. Meanwhile, HYDIN2 may have taken over the brain jobs, which is why it is exceptionally active in neurons. And its origins at the very dawn of the Homo lineage, before our brains ballooned to their current large size, make this potential role that much more exciting.

The team still need to confirm that the HYDIN2 gene is truly functional. But if Eichler is right, HYDIN2 would join a small but growing club of genes that arose through duplications, are unique to humans, and perform important functions in the brain. “The fact that these human-specific genes are still being discovered, years after the Human Genome Project, is pretty frickin’ amazing to me,” says Eichler.

Eichler has been obsessed with duplicated genes ever since he was a graduate student in the 1990s. In 2002, he produced a duplication map of our DNA, a cartography of copied genes. Since then, his team have been characterizing these sequences in many different species, and they’ve started to realize how weird the human ones are.

Duplicated genes make up some 5 percent of the human genome. Many of them have arisen in the last 10 to 15 million years, since humans, chimps and gorillas started going our separate evolutionary ways. In fact, we—the great African apes—have ended up with far more duplicated genes than, say, orangutans or macaque monkeys. No one fully understands why.

What’s clearer is that these genes are organized in a very unusual way. For example, in other mammals like elephants, rats, and platypuses, the copies tend to sit next to the originals in a tandem series. But in humans, chimps, and gorillas, they disperse across the genome.

They also have a unique architecture. Imagine a gene, G1, which gets copied into a different part of the genome, producing G2. Now, another duplication event copies G2, creating yet another copy of G1 along with some of the new DNA surrounding it. This happens again and again; with each new duplication event, the core genes picks up more flanking material. “It builds an inverse Oreo cookie,” he says, while holding his hands out and pulling them further and further apart.