When the neurons that release the neurotransmitter dopamine die, people develop Parkinson's disease. Roger J. Bick &/Brian J. Poindexter / UT-Houston/Science Source hide caption

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Roger J. Bick &/Brian J. Poindexter / UT-Houston/Science Source

Brain Cell Transplants Are Being Tested Once Again For Parkinson's

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A human embryo kept alive in the lab for 12 days begins to show signs of early development. The green cells seen here in the center would go on to form the body. This embryo is in the process of twinning, forming two small spheres out of one. Courtesy of Gist Croft, Cecilia Pellegrini, Ali Brivanlou/Rockefeller University hide caption

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Courtesy of Gist Croft, Cecilia Pellegrini, Ali Brivanlou/Rockefeller University

Embryo Experiments Reveal Earliest Human Development, But Stir Ethical Debate

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In a cluster of glowing human stem cells, one cell divides. The cell membrane is shown in purple, while DNA in the dividing nucleus is blue. The white fibers linking the nucleus are spindles, which aid in cell division. Allen Institute for Cell Science hide caption

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Allen Institute for Cell Science
Maria Fabrizio for NPR

Researchers Question Safety, Value Of Untested Stem Cell Treatments

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In this file photo, a professor holds a tray of stem cells at the University of Connecticut. The NIH plans to lift a moratorium on funding studies using human stem cells in animal embryos. Spencer Platt/Getty Images hide caption

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Spencer Platt/Getty Images

The Chimera Quandary: Is It Ethical To Create Hybrid Embryos?

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Pablo Ross of the University of California, Davis, inserts human stem cells into a pig embryo as part of experiments to create chimeric embryos. Rob Stein/NPR hide caption

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Rob Stein/NPR

NIH Plans To Lift Ban On Research Funds For Part-Human, Part-Animal Embryos

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Jeannie Phan for NPR

In Search For Cures, Scientists Create Embryos That Are Both Animal And Human

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Human stem cells, in this case made from adult skin cells, can give rise to any sort of human cell. Some scientists would like to insert such cells into nonhuman, animal embryos, in hopes of one day growing human organs for transplantation. Science Source hide caption

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Science Source

Should Human Stem Cells Be Used To Make Partly Human Chimeras?

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Image of a mini-kidney formed in a dish from human induced pluripotent stem cells. Minoru Takasato/Nature hide caption

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Minoru Takasato/Nature

Scientists Grow Primitive Human Kidneys In A Dish

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In 1954, Dr. Frederick C. Robbins, then chief of pediatrics and contagious diseases at Cleveland Metropolitan General Hospital, was one of three winners of that year's Nobel Prize in medicine. The scientists' work, which led to a vaccine against polio, was performed in human fetal cells. AP hide caption

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AP

Research On Fetal Tissue Draws Renewed Political, Scientific Scrutiny

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Loki's Castle, the field of deep sea vents between Norway and Greenland, is home to sediments containing DNA from the newly discovered archaea. R.B. Pedersen/Centre for Geobiology, Bergen, Norway hide caption

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R.B. Pedersen/Centre for Geobiology, Bergen, Norway

Missing Link Microbes May Help Explain How Single Cells Became Us

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Isabella Beukes, of Santa Rosa, Calif., has been legally blind for more than 40 years. An experimental treatment derived from embryonic stem cells seems to have enabled her now to see not just color but also some shapes. Tim Hussin for NPR hide caption

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Tim Hussin for NPR

Embryonic Stem Cells Restore Vision In Preliminary Human Test

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