We are grateful to Penny Spikins and Andy Needham and Denis Noble for advice and encouragement, to Geoff Bailey for comments on an earlier draft and to anonymous reviewers for helpful suggestions. We also thank Heather Winder for proofreading assistance. We would like to acknowledge the European Union for funding under contracts 308601 (FP7 COMPLEX project) and 269586 (ERC DISPERSE project). Figure 1 first appeared in Winder N.P. and Winder I.C.(2013), while Figures 2 and 3 originally appeared in Winder and Winder (2014).