Leonard Cockayne and evolution

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Abstract
The history of “Cockaynes” in Sheffield is first outlined as well as aspects of Leonard Cockayne's early life, his family, and the sources of his private income. Cockayne's views on the evolution of divaricatingjuvenile forms and shrubs are summarised, and then examined with special reference to the three New Zealand species of Sophora. It is concluded that Sophora microphylla with ajuvenile divaricating form did not give rise by neoteny to the divaricating shrub S. prostrata, as Cockayne suggested, but that S. microphylla is derived from hybridisation between S. prostrata and S. tetraptera. It is also suggested that all species with divaricatingjuvenile forms arose by hybridisation between a divaricating shrub and a tree. The reasons why Cockayne favoured the inheritance of acquired characters are listed, and a restatement of the problems attempted in more modem terms. The selection pressures which could have led to divarication are also discussed, and it is considered that whereas some species may have evolved in drought-prone forests, others, such as Sophora prostrata, did not. The distribution and frequency of normal and cut-leaved juvenile forms in native aralioids are described, and the cut-leaved juvenile of Schefflera digitata shown to be genetically controlled and not environmentally induced as thought by Cockayne. Extracts are given from Cockayne's letters to Sir David Prain ofKew between 1912 and 1921, showing the development of Cockayne's ideas for a book on plant evolution in New Zealand. The unpublished and incomplete manuscript, now held at the Auckland War Memorial Museum, is described. The views of Lotsy on hybridism as a factor in evolution are then examined in relation to Cockayne's later work.

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