Donald I. Williamson

Donald Irving Williamson (8 January 1922, in Alnham, England – 29 January 2016, in Port Erin, Isle of Man) was a British planktologist and carcinologist.^[1]

Education

Williamson gained his first degree from the

Works

He also published speculative works on hybridisation in evolution: Larvae and Evolution^[4] (1992, a book foreworded by Lynn Margulis and Alfred I. Tauber), The Origins of Larvae^[5] (2003, a revised and extended edition of Larvae and Evolution, not to be confounded with his 2007 article of same title published in the magazine American Scientist^[6]), and some articles on the same subject.

In Larvae and Evolution

According to Williamson, these successful hybridisations would most likely occur in organisms with external fertilisation or male gamete dispersal. He acknowledges in his work Larvae and Evolution to have borrowed the idea of hybridogenesis from the well-known process of interspecific hybridisation that take place in plants. Hybrid plants generated from phylogenetically distant species can often give rise to new species if the hybrids become reproductively isolated from the progenitor populations.^[5]

In one of his articles^[7] Williamson contends that

1. there were no true larvae until after the establishment of classes in the respective phyla,
2. early animals
   species
   ,
3. the Cambrian explosion resulted from many such hybridisations,
4. modern animal phyla and classes were produced by such early hybridisations, rather than by the gradual accumulation of specific differences.

To prove the possibility of such hybridizations, Williamson claimed to have succeeded in 1990 in fertilizing sea squirt eggs with sperm from a sea urchin (a species from a different phylum). However, it was later shown that the alleged hybrids were simply sea urchins.^[8]

Williamson's hypothesis has been reviewed in the companion website for the eighth edition of the textbook Developmental Biology.^[9]

Reception of the larval transfer theory

In an article published in the esteemed journal

Williamson's hypothesis was rebutted in response papers in the same journal issue by the biologists Michael W. Hart and Richard K. Grosberg^[13][14] and Gonzalo Giribet (Curator of Invertebrates in the Museum of Comparative Zoology at Harvard University)^[15][16] and later by Arnab De and Rituparna Bose. Even though the latter authors rectified some of the signs considered by Williamson as molecular evidence of an ancestral hybridogenesis, they recommended a laboratory hybridisation study between an onychophore and a cockroach, as proposed by Williamson.^[17]

See also

References