Hopeful monsters

Prosegue sul New York Times in blog dell'evoluzionista inglese Olivia Judson. Questa settimana Judson rivaluta l'idea degli hopeful monsters (o mostri speranzosi) del genetista Richard Goldschmidt.

Negli anni 30, insoddisfatto delle spiegazioni sulla origine di nuovi tratti morfologici fornite dalla sintesi moderna, che favoriva ipotesi basate sul lento accumulo di mutazioni con piccoli effetti fenotipici, Goldschidt avanzo' l'ipotesi che nuovi tratti morfologici potessero originare rapidamente attraverso macromutazioni (spesso causate da riarrangiamenti cromosomici e/o da mutazioni avvenute durante lo sviluppo). Secondo Goldschmidt la maggior parte di queste mutazioni avrebbe portato rapidamente alla morte degli organismi "mostruosi", ma una piccola percentuale dei mutanti si sarebbe trovata ad essere piu' adattata al proprio ambiente dei suoi conspecifici, e il fortunato mutante in quel caso diverrebbe il fondatore di una nuova linea filogenetica. Le idee di Goldschmidt non furono mai accettate dai suoi colleghi, e per decenni il suo nome e' stato accuratamente evitato da quasi tutti i principali teorici dell'evoluzione (Steven J. Gould fu una delle poche eccezioni). Negli ultimi anni progressi in discipline come genetica dello sviluppo ed epigenetica (che indicano quali meccanismi regolano l'origine di tratti fenotipici) hanno portato molti a rivalutare alcune delle idee di Goldschidt.

L'articolo di Judson puo' essere letto presso il suo sito web e fornisce una breve ma ottima lista di referenze bibliografiche.

Chi fosse interessato a saperne di piu' su Goldschidt e sulla riscoperta delle sue idee puo' anche consultare i seguenti articoli:
American Zoologist Volume 40, Issue 5 (October 2000) pp. 738-747
From Hopeful Monsters to Homeotic Effects: Richard Goldschmidt's Integration of Development, Evolution, and Genetics
Michael R. Dietrich
Richard Goldschmidt's research on homeotic mutants from 1940 until his death in 1958 represents one of the first serious efforts to integrate genetics, development, and evolution. Using two different models, Goldschmidt tried to show how different views of genetic structure and gene action could provide a mechanism for rapid speciation. Developmental systems were emphasized in one model and a hierarchy of genetic structures in the other. While Goldschmidt tried to find a balance between development and genetics, critics, such as Sewall Wright, urged him and eventually helped him incorporate population dynamics into his models as well. As such, the history of Goldschmidt's research on homeotic mutants highlights the continuing challenge of producing a balanced and integrated developmental evolutionary genetics.
Genome 46(6): 963-967 (2003)
Epigenetics and the renaissance of heresy
Susannah Varmuza
Classic neo-Darwinian theory is predicated on the notion that all heritable phenotypic change is mediated by alterations of the DNA sequence in genomes. However, evidence is accumulating that stably heritable phenotypes can also have an epigenetic basis, lending support to the long-discarded notion of inheritance of acquired traits. As many of the examples of epigenetic inheritance are mediated by position effects, the possibility exists that chromosome rearrangements may be one of the driving forces behind evolutionary change by exerting position effect alterations in gene activity, an idea articulated by Richard Goldschmidt. The emerging evidence suggests that Goldschmidt's controversial hypothesis deserves a serious reevaluation.
Genome 46: 968-972 (2003)
Comment on "Epigenetics and the renaissance of heresy"
Rama S. Singh
Lamarckian inheritance (i.e., inheritance of acquired character) and Richard Golschmidt´s concept of "systemic mutations" and their role in macroevolution have been two of the most controversial topics in the history of evolutionary biology. The concept of Lamarckian inheritance was put to rest first by Weismann´s germplasm theory and experiment and later by the discovery of Mendelian inheritance. Goldschmidt´s theory of macroevolution by systemic mutations was put to rest by the discovery of DNA´s structure and subsequent demonstration showing allelic variation as the basis for genetic and phenotypic differences observed among organisms. Some authors are using recent demonstrations of epigenetic inheritance in higher organisms to support Lamarckian inheritance and Golschmidt´s theory of macroevolution by systemic mutations. In this paper, I show that the recent discoveries related to mutations, such as the so called "directed" mutations in bacteria, and epigenetic inheritance in higher organisms are basically an extension of the notion of "mutation" and thus of the concept of "heritable variation" required for evolution. While the new discoveries of the laws of developmental transformations are enriching our knowledge of the intricate relationship between genotype and phenotype, the findings of epigenetic inheritance do not challenge the basic tenets of the neo-Darwinian theory of evolution, as other than producing new variation no new processes of evolutionary change have been added to the ones we already know - mutation, migration, selection, and drift.
Genome 46: 973 (2003)
Reply to the comment by R.S. Singh on "Rehabilitation of Lamarck and Goldschmidt or renaissance of heresy?"
Susannah Varmuza

Francesco Santini