Posts Tagged ‘mutation’

In his autobiography, Charles Darwin notes, “Towards the end of the work I gave my well abused hypothesis of Pangenesis. An unverified hypothesis is of little or no value”—the First-Wave of evolutionary thought. Today, Darwin’s sentiments on pangenesis have re-emerged, however, this time on genetics.

In this week’s edition of the journal Science published by the American Association for the Advancement of Science (AAAS), the focus is on epigenetics. An on-line issue even features a video by Science editor Guy Riddihough asking a number of top researchers a simple question: “What’s your definition of epigenetics?” And, “Their answers aren’t quite so simple,” according to Riddihough. Continue Reading

In The Origin of Species, Charles Darwin uses the term information seven times. In all seven uses, information is only used in the context of gaining knowledge, “I have also reason to suspect, from information given me by Mr. W. W. Edwards, that with the English race horse the spinal stripe is much commoner in the foal than in the full-grown animal.”

Information is never used in the context of genetics. In fact, information is only used in the context of exchanging information between colleagues.  

“And it would appear from information given me by Mr. Watson, Dr. Asa Gray, and Mr. Wollaston… ”

“… as I have learnt from information and specimens sent to me by Mr. Salvin… ”

“Mr. Agassiz, to whose great kindness I am indebted for much information on the subject… ”

“This species is found in the southern parts of England, and its habits have been attended to by Mr. F. Smith, of the British Museum, to whom I am much indebted for information on this and other subjects.”

“Accordingly I wrote to Professor Miller of Cambridge, and this geometer has kindly read over the following statement, drawn up from his information.”

“… without any information in regard to their geological position, no one would have suspected that they had co-existed with sea-shells all still living.”

Little did Darwin know that even before the publication of the fourth edition of The Origin of Species in 1866, Gregor Mendel had presented the now-famous paper entitled “Experiments on Plant Hybridization,” laying the foundations of modern genetics. Continue reading

Charles Darwin lamented in his autobiography over ascribing to pangenesis in The Origin of Species - 

Towards the end of the work I gave my well abused hypothesis of Pangenesis. An unverified hypothesis is of little or no value.

While Darwin’s hypothetic pangenesis was an accepted theory in 1859, by 1864 French biologist, Louis Pasteur, had undermined pangenesis by demonstrating that life cannot arise spontaneously—life can only come from life. Darwin was right. Pangenesis is of “no value.”

By the mid-twentieth century, while Francis Crick and James D. Watson unveiled the molecular structure of DNA. In 1953, the momentum of evolution theory was rapidly defaulting to a mutation plus natural selection neo-Darwinian model, most commonly known as Modern Synthesis.
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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.

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In 1943, published in a paper entitled “Mutations of Bacteria from Virus Sensitivity to Virus Resistance,” microbiologist Salvador Luria, biophysicist Max Delbrück, and bacteriologist and geneticist Alfred Hershey discovered that mutations occur at a constant rate. In 1969, they were awarded the Nobel Prize in Physiology and Medicine “for their discoveries concerning the replication mechanism and genetic structure of virus.”

The Luria-Delbrück Experiment opened the question, are mutations inherent to microbes for the purpose of adaption to rapidly changinging environments and not for evolution? While microbe resistance through mutation is a logical mechanism for evolution, the reality is the bacteria have remained a bacteria and the virus has remained a virus. Preexistent genetic variants determine the range of mutations. Pierre-Paul Grassé, president of the French Academy of Sciences, observed, “bacteria, the study of which has formed a great part of the foundation of genetics and molecular biology … stabilized a billion years ago.”

The question is whether the mutations are the “raw material for evolution” or nature’s means for the microbes to adapt to the environment. In a 2009 review article by entitled “Darwinian evolution in the light of genomics”, published in Nucleic Acid Research, Eugene V Koonin concluded, “There is no consistent tendency of evolution towards increased genomic complexity” through mutation as expected with current evolutionary theories. Mechanisms of evolution remain beyond any known natural law.

Reflecting on the role of mutations, Grassé questioned, “What is the use of their unceasing mutations if they do not change?” Grassé concludes, “the mutations of bacteria and viruses are merely hereditary fluctuations around a median position; a swing to the right, a swing to the left, but no final evolutionary effect.” Microbes undergo constant mutations, but do not evolve – mutation stasis.

*Nucleic Acids Res. 2009 March; 37(4): 1011–1034