Evolution

Guide to Darwins Theory of Common Descent



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In 1859, Charles Darwin wrote his famous book “On The Origin of Species.” Darwin was a deeply religious man who put forth his ideas after a long voyage on the H.M.S. Beagle spent observing a variety of animals. It revolutionized thinking and, in some circles, can still cause controversy today. It put forth two theories, common descent and natural selection, as the mechanisms through which evolution occurred.

The common descent theory states that all living creatures are ultimately descended from a single primordial form. Over time this form was subjected to different conditions in different locations. Random mutations at the genetic level influenced the survival of the organism. The beneficial mutations increased the chances of the organism succeeding in reproducing. Negative mutations cut the organism’s life short and reduced its capacity for reproduction. The accumulation of beneficial mutations ultimately results in a new organism sufficiently different from the original to be classified as a whole new species. This is how natural selection works.

The theory of common descent has been supported by evidence of transitional forms found in the fossil record. Transitional forms are animals that are in the process of becoming a new species. Evidence of common elements in all living things at the molecular level has also supported Darwin’s theory.

Most recently, a Brandeis biochemist named Douglas Theobald did a series of experiments that examined proteins found in all three domains of life–bacteria, archaea and eukarya. Archaea are unicellular organisms with free-floating DNA within the cell (they have no nucleus). Bacteria, although different from Archaea, are also unicellular with no nucleus. The eukarya include all animals with a cell nucleus that contains their DNA. His results proved Darwin’s theory conclusively.

This put to rest the opposing theory of an evolutionary web that had a few different species at its root, as opposed to Darwin’s single species from which all have descended. This is quite significant in that, in Darwin’s time, there was no way of proving any of this. Genetic and molecular biology studies were unknown.

Anaximanda, an ancient Greek philosopher, proposed that humans descended from animals long before Darwin wrote his famous book. The idea that life began from non-living elements also belonged to Anaximanda. Common descent, however, is uniquely Darwin’s. Although some will always find it difficult to accept evolutionary theory, Theobald’s studies have provided the long-sought-after proof that Darwin had it right. All life descended from a single organism by the mechanism of natural selection. 

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