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.
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!
PS, 27 February 2013. Ingeborg Reichle just alerted me to this wonderful book Trees of Life: A Visual History of Evolution by Theodore W. Pietsch
Image (taken by B Nerlich): Nottingham, Arboretum