Image copyright Keith Karracker Image caption Steve Silberman is an award-winning science writer

Author Steve Silberman has won the £20,000 Samuel Johnson Prize for Non-Fiction for his book about autism.

The judges said Neurotribes: The Legacy of Autism and How to Think Smarter About People Who Think Differently was a "tour de force" of journalistic and scientific research.

It is the first popular science book to win the prize in its 17-year history.

The shortlist had included Jonathan Bate's Ted Hughes: The Unauthorised Life and Robert Macfarlane's Landmarks.

Historian Anne Applebaum, chair of the judges, praised Silberman's "compassionate journalism" and said he excelled at using stories and anecdotes to explain complex medical issues to a wide audience.

The American author, who is based in San Francisco, has been a science writer for Wired and other magazines such as the New Yorker, the MIT Technology Review, Nature and Salon for more than 20 years.

"We admired Silberman's work because it is powered by a strongly argued set of beliefs: that we should stop drawing sharp lines between what we assume to be 'normal' and 'abnormal', and that we should remember how much the differently-wired human brain has, can and will contribute to our world," Applebaum said.

"He has injected a hopeful note into a conversation that's normally dominated by despair."

Neurotribes, she added, was "a tour de force of archival, journalistic and scientific research, both deeply researched and widely accessible".

In its review of Silberman's book, The Guardian described Neurotribes as "a gripping narrative written with journalistic verve".

The £20,000 Samuel Johnson Prize was won last year by Helen Macdonald's H is for Hawk.

Image copyright Samuel Johnson Prize

The Samuel Prize 2015 shortlist: