Posts Tagged ‘pangenesis’

Charles Darwin, desperate to discover how evolution keeps going, in 1865, sent his good friend, Thomas Huxley, a thirty-page manuscript under the heading “The Hypothesis of Pangenesis.” Huxley’s response must have been discouraging, since Darwin replied, “I do not doubt your judgment is perfectly just and I will persuade myself not to publish. The whole affair is much too speculative.”

Pangenesis extended Aristotle’s concept of “spontaneous generation,” later popularized by French naturalist Jean-Baptiste Lamarck. Still anxious, two years late in 1867 Darwin sent a letter to American scientist, Asa Gray at Harvard University -

The chapter on what I call Pangenesis will be called a mad dream, and I shall be pretty well satisfied if you think it a dream worth publishing; but at the bottom of my own mind I think it contains a great truth.

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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

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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Pangenesis was Darwin’s hypothetical mechanism for the origin of variation and inheritance through particles called gemmules. This “provisional hypothesis” on the origin of variation was presented in his 1868 work The Variation of Animals and Plants under Domestication through gemmules acquiring new variations that brings “together a multitude of facts which are at present left disconnected by any efficient cause”.

The etymology of pangenesis comes from the Greek words pan (a prefix meaning “whole”, “encompassing”) and genesis (birth) or genos (origin). Gemmules were thought to learn from experiences.

The origin of new variations was critical for Darwin’s theory since the “slight, successive” changes in evolution requires a constant stream of new variations for the actions of natural selection. Gemmules were imagined particles. These learned gemmules particles sent from every cell (pan) in the body with new variations (genos) accumulated in the germ cells and had a ‘vote’ in the constitution of the offspring (genesis).

This hypothesis provided a possible mechanism for the inheritance of acquired characteristics, as proposed by Jean-Baptiste Lamarck, which Darwin believed to be the origin of new variations in living organisms.

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.

Although, Mendel’s discovery went unnoticed until the turn of the twentieth century, German biologist August Weismann, at the University of Freiburg, launched the first scientific evidence directly challenging Darwin’s theory. Now known as the “Weisman Barrier,” in 1883, Weismann cut off the tails of mice from 21 generations. Seeing that the 22^nd generation still had tails, Weismann concluded that the evidence contradicted Darwin’s theory of pangenesis despite obvious reasons for change in the mice, “continuity” was observed, not new variations.

Ernst Mayr, Darwin’s twentieth-century bull-dag, stated Weismann as “The second most notable evolutionary theorist of the 19th century.” What is still unresolved now 150 years later is—what is the origin of variation?