Liu, Jean
Milne, Glenn A.
Kopp, Robert E. http://orcid.org/0000-0003-4016-9428
Clark, Peter U.
Shennan, Ian
Article History
Received: 15 May 2015
Accepted: 10 November 2015
First Online: 21 December 2015
Competing interests
: The authors declare no competing financial interests.