HONG KONG (AP) — A Chinese researcher claims that he helped make the world’s first genetically edited babies — twin girls born this month whose DNA he said he altered with a powerful new tool capable of rewriting the very blueprint of life.

If true, it would be a profound leap of science and ethics.

A U.S. scientist said he took part in the work in China, but this kind of gene editing is banned in the United States because the DNA changes can pass to future generations and it risks harming other genes.

Many mainstream scientists think it’s too unsafe to try, and some denounced the Chinese report as human experimentation.

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Also see: He did it: uproar over Chinese gene-edited babies

In the video, Dr. He Jiankui, who has stated he genetically altered twin girls among others, explains his work. His demeanor is so pleasant it is hard to feature him as a Dr. Jekyll.