A scientist in China claims to have created the first genetically modified humans.
The research, led by HeJianku of Shenzhen, took embryos for seven couples during fertility treatments, which resulted in the birth of twin girls, named Lulu and Nana.
Shenzhen claims to have used a genome-editing tool, called CRISPR, to modify the genes of the babies so that they will have a resistance to the AIDS virus.
This kind of gene editing is banned in the United States because it risks harming other genes.
Scientists around the world are concerned about this use of CRISPR. It has been used by many researchers to modify animal DNA, but never in this way.
"It's troubling because we don't have an international consensus on how this type of research could or should be ethically conducted," said Kimberly Cooper, an assistant professor at the University of California, San Diego.
Cooper said before CRISPR, it would have required up to 700 animals to get the same effects scientists can get in a single animal now.
"As soon as CRISPR was implemented in a variety of species it cust the costs," said Cooper, "And made it almost trivial to make many other mutations that model disease and help us understand how genes work in cells."
Separate from CRISPR, Cooper's research at UCSD is one of the only labs in the world that is studying the genetics of Jerboa rodents to find out how disease forms.
She hopes that the research will help lead to future cures for diseases like Alzeheimer's and diabetes in humans.