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Charles Darwin & the Evolutionary Tree of Life
his three major theory approaches

Charles Darwin made three major approaches to the Tree of Life concept in his evolutionary theory.

A one-time theology student in training to become a minister of religion, albeit one with a passionate interest in natural history field studies, Darwin was informally recruited as a geological advisor to accompany british naval Captain Fitzroy on a surveying voyage to South America and the Pacific Ocean.

This voyage, on board HMS Beagle, lasted some five years from 1831 to 1836 and helped to transform the would-be country parson into a theologically skeptical man of science.

Darwin - Tree of Life Approach 1 - his "Eureka" moment?
His notebook sketch of 1837

Charles Darwin's Tree of Life Sketch 1837
Charles Darwin's Tree of Life sketch shows his early theoretical insight of how a genus of related species might originate by divergence from a starting point (1).

The text annotations read:-

I think

Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction.

Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction. Thus genera would be formed. — bearing relation (page 36 ends - page 37 begins) to ancient types with several extinct forms...

From Darwin's Notebook B now stored in Cambridge University library

Darwin - Tree of Life Approach 2 - an aide to his argument?
His diagram from The Origin of Species of 1859

This diagram, which is a significant updating of Charles Darwin's original Tree of Life sketch of 1837, is the only illustration in the Origin of Species and is referred to develop several key arguments:-

... After the foregoing discussion, which ought to have been much amplified, we may, I think, assume that the modified descendants of any one species will succeed by so much the better as they become more diversified in structure, and are thus enabled to encroach on places occupied by other beings. Now let us see how this principle of great benefit being derived from divergence of character, combined with the principles of natural selection and of extinction, will tend to act.
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Darwin quotes
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Thomas Henry Huxley
Darwin's Bulldog

 

The accompanying diagram will aid us in understanding this rather perplexing subject.

The Tree of Life diagram already just mentioned is referred to extensively, as an aide to his scientific / conceptual argument, in Chapter IV., entitled Natural Selection, of Darwin's seminal work Origin of Species of 1859.

This section from the chapter on Natural Selection from Darwin's Origin of Species is available here:-

Tree of Life diagram with accompanying text : Origin of Species 1859

Darwin - Tree of Life Approach 3 - His chapter summary
"Chapter IV. Natural Selection" - Origin of Species 1859


Chapter IV., entitled Natural Selection, from The Origin of Species is ended with an explicit chapter summary by Charles Darwin himself in these words:-

The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have at all times overmastered other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was young, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear the other branches; so with the species which lived during long-past geological periods, very few have left living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these fallen branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only in a fossil state. As we here and there see a thin, straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.

 

 

Another Sketch about Life


If Charles Darwin were alive today we at Age-of-the-Sage would be urgently seeking to interest him in our discovery of the fact that there is close agreement between several major World Faiths, Plato, Socrates, Pythagoras and Shakespeare in suggesting that Human Wisdom / Spirituality is relative to Human Desire / Materialism and to Human Wrath / Ethnicity.

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Charles Darwin & the Tree of Life
his three major approaches