Darwins Tree Of Life Metaphor Essays

Given that most people do not have advanced degrees in mathematics or the sciences, debates and discussions surrounding evolution and creationism appear in the public square in the form of competing metaphors, similes, and extended analogies.

In other words, we use metaphors, similes, and extended analogies to simplify and grasp issues that might be otherwise inaccessible to us.

Hence we can keep a look-out for the ways in which our use of language, especially metaphorical language, frames and structures discussions of evolution and creationism.

Today’s metaphor comes from the end of chapter 4 of Charles Darwin’s Origin of Species (1859), and concerns Darwin’s description of life as “a great tree.”

A tree or plant that confers long, or even eternal, life upon those who eat of it has long associations in Western cultural history—going back, in Mesopotamia, to the Epic of Gilgamesh, and in the Levant, to the Book of Genesis (2:9).

In the New Testament, the writer of Revelation makes a promise, in the voice of Jesus, to persecuted Christians:

To him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God. (2:7)

In all cases in ancient Western literature, access to life-giving plants or a “tree of life” is allusive. The tree of life is not something that one is a part of, or embedded in, but something to which one is outside of, and strives toward, in the hope of gaining its fruit.

It is thus ironic that Charles Darwin’s metaphor of life as a “great tree” should be built on death and mass extinction, and implicitly embed humans, whether we like it or not, into one of its branches.

Darwin’s metaphor of life as a “great tree” thus marks a stark break from traditional Western cultural and religious associations of trees with life.

But Darwin’s extended analogy of life on earth with a great tree is extraordinarily beautiful, arguably the most beautiful passage in all of his Origin of Species, and Darwin even suggests that the simile so closely matches the actual reality of things that it should be taken literally; that is, as the substantial truth regarding the way things really are. Here’s Darwin’s passage in full:

The affinities of all 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 each former year 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 tried to overmaster 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 small, budding twigs; and this connection 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 all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representative, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down on a tree, and which by some chance has been favored and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Leidosiren, 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.

The conclusion of this passage is particularly jarring, for Darwin equates the tree’s dropped off branches, overlaid with soil and sinking into the earth, with the fossil record—and calls this process of creation and destruction “beautiful.”

It is thus difficult not to hear in the conclusion of the passage a sly attempt by Darwin to trigger pleasurable associations of death and eros, as in the frequent Victorian artistic portrayals of the dying away of beautiful maidens, such as Shakespeare’s Ophelia and King Charles’s fourteen year old daughter on the Isle of Wight.

And Darwin’s actual using of the phrase “Tree of Life”—set in capital letters—allowed his analogy to carry with it, at its climax, all the religious and traditional associations—and counter-associations—that one might be tempted to make with it. 

This passage thus shows that Darwin was not just a great scientist—he was also a skilled writer who knew how to use language to powerful rhetorical and emotional effect.

In the 21st century, Darwin’s once potentially scandalous analogy has reached the status of cliche—and it is difficult today not to think of life in this manner.

Darwin’s tree simile is part of the basis, not just for evolutionary thinking, but ecological thinking.

And when first pointed out to us, it is hard not to respond with recognition, as if encountering a revelation:

Of course life is interconnected and like a branching tree. How did the world miss this observation for so long?

This is the power of metaphorical language.

Below is the image of a tree in which an artist has carved animals. And beside it is a more traditional image of the Tree of Life, from Assyria, early in the first millenium BCE, in which two divine beings guard the Tree of Life:

In thinking about these two images, it occurs to me that science attempts to explain to us why we are part of one tree, and religion attempts to explain why we have been excluded from another one.

The great human existential quest is how to move from the tree of Darwinian life to the tree of eternal life (or some form of immortality).

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This entry was posted in Uncategorized and tagged agnostic, atheist, biology, Charles Darwin, creation, evolution, intelligent design, John Macarthur, literature, metaphor, poetry, Santi Tafarella. Bookmark the permalink.

October 22, 2012, by Brigitte Nerlich

Metaphor, image and now visualisation: Darwin’s tree of life

Yesterday I came across this tweet: “Richard Dawkins ‏@RichardDawkins Zooming into the Tree of Life. Magnificent piece of software, brilliantly intuitive visualisation of the tree of life http://bit.ly/PJyox3 Retweeted by Eric Sawyer”

This led me to a fascinating interactive and fractal representation of the tree of life (or phylogenetic tree or evolutionary tree) created by Imperial College which went ‘live’ on 16 October. The interactive website is called OneZoom™. This in turn made me reminisce about the long way this tree has come, how it grew and how it might be growing in the future, making science, in this case evolutionary biology, public along the way.

[Here is a nice description by Jerry Coyne; added 30 April 2016]

Trees growing between fields

As a historian of historical linguistics I have always been interested in trees, especially trees that grow between fields…. Let me explain. I once delved into the history of historical linguistics, especially the time at the beginning of the nineteenth century when August Schleicher, William Dwight Whitney, Arsène Darmesteter and Michel Bréal (amongst others) speculated about the life and growth of language(s) and the life and growth of words etc. They were inspired by what was happening in geology and biology at the time especially with relation to the works of George Cuvier, Jean-Baptiste Lamarck, Charles Lyell, Charles Darwin, Hensleigh Wedgwood, Ernst Haeckel and others.

Central to the thinking of all those scholars was finding out about what one may call branching patterns of either biological or linguistic ‘organisms’ (real or metaphorical). Using the branching or tree metaphor to represent patterns in the evolution of species, Darwin is well-known for having drawn the first phylogenetic tree with the little caveat beside it: ‘I think’. Darwin was using a verbal and a visual metaphor: ‘the tree of life’. Now, metaphor can be said to be “a conjecture on the nature of reality” (Du Preez, 1991). In this case we are dealing with a very big conjecture on the nature of reality, the reality of nature and the nature of life. One of the most profound conjectures in the history of science, perhaps. August Schleicher too drew a tree, a family tree or ‘Stammbaum’, of language families. You can find images of both trees in this nice blog by a historical linguist, Lisa Minnick, underneath the rather wonderful blog title ‘Darwin and Schleicher sitting in a tree’. As Lisa Minnick points out, Schleicher created one of the most enduring linguistic metaphors, namely that of the phylogenetic tree for mapping language descent and relatedness. Trees were in the air at the time, it seems.

Darwin drew his tree in a notebook in 1837, unbeknownst to Schleicher and it went public in 1859 with the publication of On the Origin of Species. Schleicher (an amateur botanist, by the way) drew his tree in 1853 unbeknownst to Darwin. They later came to know of each other and their respective trees through Haeckel, and Darwin mentioned Schleicher in The Descent of Man.

A tree growing in the open

However, the tree metaphor didn’t endure in linguistics as much as it did in biology.  It was replaced by wave, web and other models and metaphors. By contrast, Darwin’s conjecture, metaphor and drawing grew into a theory and the theory came to be bolstered by data, increasingly BIG DATA. This is where the tree meets modernity, so to speak, in the form of modern data visualisation technologies. There are many attempts to visualise the tree of life, such as this visualisation by the Wellcome Trust for example and there are probably many others. Most importantly perhaps, there is now the Open Tree of Life Project. The tree of life has its roots now in cyberspace and in the cyber-community. It is open access and open source.

This brings us back to the OneZoom visualisation of the tree of life. Darwin and Schleicher drew their trees on paper with pen and ink and their trees were distributed using the printing press. Today’s tree is a post-ink tree, so to speak. In the OneZoom press release this is made clear: “The traditional tree of life is generally drawn starting with a thick trunk that represents the first life on earth. The trunk then splits into large boughs for different categories of life such as plants and animals, then ever smaller branches for groups such as insects, fish, birds and mammals. The amount of information the tree can show is usually constrained by the size of the paper it’s viewed on, but Dr Rosindell saw a way to overcome this problem, taking advantage of the unlimited space in the digital world.”

It should be pointed out that OneZoom only features the tree of mammals at the moment but the content and the tree will grow in the future as more data become available, especially through projects such as the Open Tree of Life Project.

I can’t wait!

Added 27 February 2013. Ingeborg Reichle just alerted me to this wonderful book Trees of Life: A Visual History of Evolution by Theodore W. Pietsch

Added 13 August 2014. Natalio Krasnogor retweeted a tweet mentioning a fascinating book: Aristotle’s Ladder, Darwin’s Tree: The Evolution of Visual Metaphors for Biological Order

Added 4 March 2015: A new visualisation of the tree of life as a (cosmological) spiral: http://phys.org/news/2015-03-grand-tree-life-clock-like-trend.html

Added 27 April 2015: Interesting paper by Shaaron Ainsworth etc. on using tree of life in museums settings and teaching of evolution!

Added 2 August 2015: The tree of life gets a make-over HT @carlzimmer

Image (taken by B Nerlich): Nottingham, Arboretum

Posted in evolutionary biologyMetaphorsopen accessvisualisation

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