Science & Technology

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Copyright 2016 Fresh Air. To see more, visit Fresh Air.

TERRY GROSS, HOST:

Copyright 2016 Fresh Air. To see more, visit Fresh Air.

TERRY GROSS, HOST:

It's one of the biggest medical mysteries of our time: How did HIV come to the U.S.?

By genetically sequencing samples from people infected early on, scientists say they have figured out when and where the virus that took hold here first arrived. In the process, they have exonerated the man accused of triggering the epidemic in North America.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

This presidential election year has tested the limits of free speech on Twitter. It's a prime political platform for Republican candidate Donald Trump, for the correspondents covering both presidential candidates, and for the purveyors of hate speech.

Emily Bell is the director for the Tow Center for Digital Journalism at the Columbia Journalism School. NPR's Steve Inskeep talked with Bell about the challenges Twitter faces.


Interview Highlights

On the quality of debate on Twitter

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