title: Evolution: how do characters evolve?
abstract: Ricklefs claims to show that morphological evolution in birds is associated with speciation events--that is, it is punctuational--by inference from data on only species number, clade age and character variance from a range of passerine clades. He suggests that variance increases in proportion with clade age under gradual change, but in proportion to the logarithm of species number if change is punctuational. Here I show that both clade age and the logarithm of species number independently predict variance under both gradual and punctuational change, rendering Ricklefs' results uninformative about his central hypothesis.
authors.affiliation: Department of Biological Sciences, Imperial College London, Silwood Park Campus, Ascot, Berks SL5 7PY, UK. a.purvis@imperial.ac.uk
authors.forename: Andy
authors.initials: A
authors.lastname: Purvis
mesh_terms: D000375:Aging / Q000502:physiology; D000818:Animals; D044822:Biodiversity; D005075:Biological Evolution; D014644:Genetic Variation / Q000235:genetics; D008136:Longevity / Q000502:physiology; D008954:Models, Biological; D010802:Phylogeny; D015203:Reproducibility of Results; D012107:Research Design; D020308:Songbirds / Q000033:anatomy & histology* / Q000145:classification / Q000235:genetics / Q000502:physiology*; D013045:Species Specificity; D013997:Time Factors