N. H. Barton, “Differentiation,” in Encyclopedia of Biodiversity, 2nd ed., Elsevier, 2013, pp. 508–515.

B. Halliday, N. H. Barton, and G. Hewitt, “Electrophoretic analysis of a chromosomal hybrid zone in the grasshopper Podisma pedestris,” Biological Journal of the Linnean Society, vol. 19, no. 1. Oxford University Press, pp. 51–62, 1983.