Hopeful monsters

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

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