It seems to me that for Darwin the pulsing of evolutionary rates was a strictly vertical phenomenon.

ISBN 0-674-63906-5. In 1939 he was elected a Corresponding Member of the Royal Australasian Ornithologists Union. 1007/BF01640607.

Ernst Mayr approached the problem with a new definition for the concept of species. Ernst Walter Mayr (July 5 1904 – February 3 2005) was one of the 20th century's leading evolutionary biologists.