FILE - In this Oct. 25, 2018, file photo, Rep. Mark Meadows, R-N.C., speaks to media on Capitol Hill in Washington. Lawmakers clashed over science, ethics and politics Thursday, Dec. 13, at a House hearing on using fetal tissue in critically important medical research, as the Trump administration reviews the government’s ongoing support for such studies. “Most of my constituents don’t understand when you harvest baby parts, why that is OK,” said Meadows, who chaired the hearing by the Oversight & Government Reform committee. (AP Photo/Carolyn Kaster)

In this Oct. 9, 2018, photo, Zhou Xiaoqin installs a fine glass pipette into a sperm injection microscope in preparation for injecting embryos with Cas9 protein and PCSK9 sgRNA at a lab in Shenzhen in southern China's Guandong province. China's government on Thursday, Nov. 29, 2018, ordered a halt to work by a medical team that claimed to have helped make the world's first gene-edited babies. (AP Photo/Mark Schiefelbein)

FILE- In this April 26, 2006 file photo, John Kelly Jr. fishes for striped bass in Boston Harbor. A canary in a coal mine? How about a flounder in a harbor? Offering a rare bit of good environmental news, scientists have documented a dramatic rebound in fish health they say shows how once horribly polluted Boston Harbor has cleaned up its act. (AP Photo/Elise Amendola, File)

FILE - In this Sept. 8, 2015 file photo, a reluctant student is pulled into the first day of kindergarten at an elementary School in Clio, Mich. A study shows the youngest children in a classroom are more likely to be diagnosed with attention deficit hyperactivity disorder. It’s an intriguing finding for parents considering what’s called “kindergarten redshirting,” or delaying school entry. Researchers say doctors should be aware of how classroom comparisons shape diagnosis. The paper was published Wednesday, Nov. 28, 2018, by the New England Journal of Medicine. (Christian Randolph/The Flint Journal via AP, File)

In this Oct. 9, 2018 photo, Zhou Xiaoqin, left, loads Cas9 protein and PCSK9 sgRNA molecules into a fine glass pipette as Qin Jinzhou watches at a laboratory in Shenzhen in southern China's Guangdong province. Chinese scientist He Jiankui claims he helped make world's first genetically edited babies: twin girls whose DNA he said he altered. He revealed it Monday, Nov. 26, in Hong Kong to one of the organizers of an international conference on gene editing. (AP Photo/Mark Schiefelbein)

In this Monday, April 21, 2008 file photo, a U.S soldier looks through the scope of his weapon during a night patrol in Mandozai, in Khost province, Afghanistan, seen through night vision equipment. About 400,000 veterans had a PTSD diagnosis in 2013, according to the Veterans Affairs health system. (AP Photo/Rafiq Maqbool)

FILE - In this Thursday, Oct. 11, 2012 file photo, a pedestrian talking on a cellphone is silhouetted in front of a fountain in Philadelphia. Two U.S. government agencies are giving conflicting interpretations of a safety study on cellphone radiation: One says it causes cancer in rats. The other says there's no reason for people to worry. (AP Photo/Matt Rourke)