Rosenberg et al. [29] give a detailed discussion of the issue, and of the question of whether clines or clusters are a better description of human genetic variation.
http://plosgenetics.org/article/info:doi/10.1371/journal.pgen.0020190#article1.body1.sec3.p2
In this sentence, the reference given as [29] should be [31]. The correct reference is :- Rosenberg N, Mahajan S, Ramachandran S, Zhao C, Pritchard J, et al. (2005) Clines, clusters, and the effect of study design on the inference of human population structure. PLoS Genet 1 (6): e70.
