Fruit Fly, 100 Years Later

 

The fruit fly is celebrating 100 years of research. Charles W. Woodworth at the University of California, Berkley, at the turn of the twentieth century, was the first to use the fruit fly as model in the study of genetics. Today, Drosophila melanogaster, the common fruit fly, has become one of the most studied organisms in biological research, particularly in the field of genetics.

In 1910 following Woodworth’s footsteps, at Columbia University from the top floor of Schermerhorn Hall, now known as the Fly Room, Thomas Hunt Morgan confirmed and extended Gregor Mendel’s basic principles of genetics. A year later, Morgan published his findings in Science, establishing the foundation for the emerging neo-Darwinism movement.

Morgan, in the book entitled The Mechanism of Mendelian Inheritance (1915) demonstrated how mutations using radiation on two-winged fruit flies resulted in four-winged fruit flies. The four-winged fruit fly was widely heralded as the earliest evidence that the first evolutionary step to produce a new species was a mutation.

The question, however, centered on whether the mutated four-winged fruit fly was a new species or an unsustainable aberrational freek. By 1963 after decades of research, the question could be answered definitively. Ernst Mayr, Charles Darwin’s twentieth century Bulldog, viewed the mutated four-winged fruit flies as “such evident freaks that these monsters can be designated only as ‘hopeless.’ They are so utterly unbalanced that they would not have the slightest chance of escaping elimination.” Mutation is not the gateway to evolution.

While mutations on the two-winged fruit fly served as a window to study theroretical evolutionary genetics for decades, mutations are now known not supply the raw materials for evolution. Italian geneticist Giueseppe Sermonti explains –

One spur to research on mutations was the hope that an accumulation of these might lead to a new species. But this never happened.

The fruit fly as a model for evolution via mutations gets even worse—there are no “slight, successive” genetic changes even between over 1,400 closely related Drosophila species.

The number of nucleotide base pairs Drosophila species ranges from 127 to 800 million. The probability of constructing a Tree of Life with “slight, successive” changes in nucleotide base pairs from species to species approaches the realm of impossible.

Each species of Drosophila appears to remain distinct and unique. The following table is the number of estimated genome sizes as measured by the number of nucleotide base pairs in several different Drosophila genomes.

Pierre-Paul Grassé, past-president of the French Academie des Sciences in the book entitked  Evolution of Living Organisms concludes – “The fruit fly [Drosophila melanogaster],the favorite pet insect of the geneticists, whose geographical, biotopical, urban, and rural genotypes are now known inside out, seems not to have changed since the remotest times”—evolution never happened. 

No wonder genetic researchers at Bioinformatics Research Center, North Carolina State University now bring into question whether genes even play a role in evolution between related Drosophila species. Wen-Ping Hsieh and collegues published in Genetics

An emerging issue in evolutionary genetics is whether it is possible to use gene expression profiling to identify genes that are associated with morphological, physiological, or behavioral divergence between species and whether these genes have undergone positive selection. (1)

Genetic researchers from the Department of Ecology and Evolutionary Biology, University of Arizona, similarly discovered that “no strong evidence” in gene selection exists between Drosophila species and the respective proteins produced, “divergent expression”. Between Drosophila species, changes in genes do not correllate with changes in proteins. Jeffrey M. Good and collegues in an article published in Molecular Biology and Evolution, 2006, conclude

Overall, we found no strong evidence for an increase in the incidence of positive selection on protein-coding regions in genes with divergent expression in Drosophila (2)

Genomic research looking for the “slight, successive” genetic changes required by neo-Darwinism is no friend of evolution. The survivors of 100 years of lab torture continue just as fruit flies.

The genome of D. melanogaster was sequenced in 2000. Most surprisingly, nearly 75% of known human disease genes are now known to have a recognizable match in the genetic code of fruit flies, and 50% of fly protein sequences have mammalian homologs. Mutations are either neutral or lead to disease—not evolution.

Today, over 100 years later, Drosophila serves as a genetic model for several human diseases including the neurodegenerative disorders Parkinson’s, Huntington’s, spinocerebellar ataxia and Alzheimer’s disease.

Reflecting on the limits of genetics in establishing the validity of evolution, Italian geneticist Giuseppe Sermonti weighs in –

Science has taken on the great wager … and lost.

1.  Wen-Ping Hsieh, Tzu-Ming Chu, Russell D. Wolfinger, and Greg Gibson. Mixed-Model Reanalysis of Primate Data Suggests Tissue and Species Biases in Oligonucleotide-Based Gene Expression Profiles. Genetics. 2003. 165: 747-757

2.  Jeffrey M. Good, Celine A. Hayden, and Travis J. Wheeler. Adaptive Protein Evolution and Regulatory Divergence in Drosophila. Molecular Biology and Evolution. 2006, 23(6):1101-1103

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Darwin, Then and Now is a journey through the most amazing story in the history of science - the history of evolution. The book encapsulates who Darwin was, what he said, and what scientists have discovered since the publication of The Origin of Species in 1859.

With over 1,000 references, Darwin Then and Now is a historical chronicle of the rise and fall of the once popular theory of biological evolution.

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