Posts Tagged ‘Weismann Barrier’

Vestiges: Evidence for Evolution? Part III

 

Vestiges  are tauted as evidence for biological evolution based on the Larmarckian concept of “use and disuse” that Charles Darwin reluctantly, yet fully accepted by the 6th edition of The Origin of Species in 1872.

In the 1st edition Darwin wrote that“use and disuse seem to have produced some effect” that was later changed to “use and disuse seem to have produced a considerable effect” in the 6th edition. For Darwin, the importance of “use and disuse” increased from “some effect” to “considerable effect.”

In this series, we are examining the concept that the human appendix is a vestige structure through the process of “disuse.” Vestiges are thought to be biological elements that have lost their function through “disuse.” At issue is—what is the evidence that the process of “disuse” can actually produce vestiges?

In the decade following the publication of the 6th edition, German biologist August Weismann, at the University of Freiburg, launched the first scientific inquiry to directly challenging Darwin’s theory. Now known as the “Weisman Barrier” in 1883 Weismann cut off the tails of mice from twenty-one generations. Seeing that the twenty-second generation still had tails, Weismann concluded that the evidence contradicted Darwin’s theory of “disuse” and that despite obvious reasons for change in the mice, “continuity” was observed, not new variations.

The concept of the Weismann Barrier became central to the emerging  Modern evolutionary synthesis. “Disuse” alone simply does not result in vestige structures. Ernst Mayr, known as Darwin’s bulldog of the twenty-first century, called Weismann “the second most notable evolutionary theorist of the nineteenth century, after Charles Darwin.”

Evidence from the Weismann Barrier continues to stand unchallenged, now for over 100 years. Even more to the point, after thousands of years of circumcision, “disuse” has failed to any effect on human anatomy. Without scientific experimental evidence demonstrating that “disuse” can result in any biological changes, the concept of vestige as evidence for evolution remains untenetable.

Other known vestige problems for evolution include, 1) the appendix is not found systematically found through nature, even in mammals; 2) “vestige” structures are now known to be functional. These evolutionary contradictions for vestiges continue to undermining evidence for evolution.

In the up-coming posts, we will continue to explore why these last two problems have completely undermined the concept that the human appendix is a vestige structure.

Pangenesis

I Think Cropped-1Pangenesis 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 22nd 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?



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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; encapsulating 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’s life, climaxing with the search for a natural law of evolution, is investigated in the context of the scientific evidence since discovered in the fossil record, embryology, molecular biology and genetics. Darwin The and Now is a historical chronicle of the rise and fall of biological evolution.

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