Contradictory messages in phylogenies

Jul 30 2012 Published by under Uncategorized

We are often told that a picture is worth a thousand words, and so I guess that mis-communication will be several-fold greater with a diagram than with a sentence. This certainly seems to be true in evolutionary biology, which is a pity because the visual representation of a phylogeny is such a powerful tool for communication.

I have emphasized in previous posts that the principal problem interpreting a phylogeny is seeing a single linear sequence of evolution rather than seeing an inter-connected set of lineages. I am sorry to say that many phylogenies are drawn so that it is very easy to discern a single lineage from within the set of lineages, which is thus almost guaranteed to be a source of mis-communication.

This issue seems to have started with Ernst Haeckel in the late 1800s. Haeckel was an important scientist as well as a popularizer of science (and also a brilliant artist). He coined many words that are common today in evolutionary biology (including "phylogeny"), because he was the first to study several new fields. He is often credited as the first person to publish phylogenetic trees following the publication of Charles Darwin's Origin of Species, but he was actually beaten by several people (including Franz Martin Hilgendorf, St George Jackson Mivart and Albert Gaudry). However, it is definitely true that "more people by the turn of the century had learned of evolutionary theory through Haeckel's depictions than even from Darwin's own writings" (Richards 2011).

Haeckel's first phylogenies (published in 1866) were drawn as multi-branched bushes, rather similar to the diagram that Darwin himself had published. These diagrams were intended to represent ideas about continuity of descent through time, and the role of speciation in increasing biodiversity and extinction in counter-balancing this. They thus emphasized the branching nature of variational evolution.

From Haeckel (1866). Note that Homo is on a side-branch in the top right-hand corner.

However, Haeckel then veered away from this approach when explicitly discussing the evolution of humans. Here, he drew trees with a distinct central trunk and much smaller side-branches (presumably modeled on an oak tree, rather than a bush). This image emphasizes one particular lineage at the expense of the others, because there is one taxon obviously sitting at the crown of the tree while the others are relegated to side-branches. As Richards (2011) has noted: "Haeckel regarded these two types of diagrams as having different purposes. The first represented ... a proper stem-tree, one highly branched. The latter diagram simply looked back from a given organism — in this case man — to its lineal progenitors. It's as if one began with the first kind of tree and traced back the series of man's direct ancestors — and this would result in that second kind of tree."

From Haeckel (1874). Note that Homo is at the top of the central trunk.

It should be obvious that the second diagram is much more prone to be incorrectly interpreted as transformational evolution than is the first diagram. Indeed, it is very close to a "tree" version of Huxley's human evolution diagram as discussed in my earlier blog post. And like Huxley's picture, Haeckel's tree has made it into the 20th century, as shown in the next picture.

From Smallwood et al. (1948). Note that Homo is at the top of the central trunk.

This approach to drawing a phylogeny can be used to put any chosen organism at the crown of the tree, not just human beings, as illustrated by the following diagram from James Scott (which looks like it is modeled on a pine tree). This is a fundamental characteristic of a phylogeny — it can be drawn so that any part of the diagram is at the crown. However, to be accurate it should always be drawn so that no one lineage is emphasized over any other one — there should be no taxa sitting at the crown.

From Scott (1986). Note that butterflies are at the top of the central trunk.

The issue here is that emphasizing one lineage at the expense of the others is inappropriate. The phylogeny shows the relationships of all of the taxa, and those relationships are reciprocal (brothers and sisters are equal). Emphasizing a single lineage seems to add information to the phylogeny (one taxon is more important than the others), but that extra information is false. The phylogeny is thus mis-interpreted.

If you are interested to see a modern version of human evolution that does not emphasize any one lineage, then one of the best examples is the phylogeny of ~3,000 species, based on ribosomal-RNA gene sequences, produced by the people in the Hillis/Bull laboratory at the University of Texas. You can see (and download, since it is not small!) the diagram here. Note that the diagram says "You are here", to indicate the location of the Homo lineage.

Finally, trees with a central trunk also occur outside biology. Most parts of human culture have a history of some sort that is analogous to variational evolution, with many descendant lineages arising from a single ancestor. This next diagram shows the history of jazz music in the U.S.A. Note that it is drawn as a tree with a central trunk, thus implying that each form of jazz was derived from a single previous form. This is incorrect, as any jazz afficionado will tell you, because the evolutionary history of jazz is more complex than this. Furthermore, all that the side branches are doing in this example is listing some of the practitioners of each type of jazz. This is not what the branches should mean in an evolutionary diagram.

The Story of Jazz in the U.S.A.

My basic point in this post is that evolutionists often present ambiguous evolutionary diagrams, ones that leave themselves open to an unintended transformational interpretation in addition to the intended variational one. It is the branching sequence that matters in a phylogeny, but it is incorrect to "see" the diagram as a tree with side-branches — all lineages are equally important in a phylogenetic bush because they are all equally part of the genealogical history.

In the next post I will look at more subtle ways that a single lineage can be "extracted" from a phylogeny, thus resulting in evolutionists mis-communicating with their audience.

References

E. Haeckel (1866) Generelle Morphologie der Organismen. Reimer, Berlin.

E. Haeckel (1874) Anthropogenie oder Entwickelungsgeschichte des Menschen. Engelmann, Leipzig.

R.J. Richards (2011) Images of evolution. American Scientist 99: 165-167.

J.A. Scott (1986) The Butterflies of North America: a Natural History and Field Guide. Stanford University Press, Stanford.

W.M. Smallwood, I.L. Reveley, G.A. Bailey, R.A. Dodge (1948) Elements of Biology. Allyn & Bacon, Boston.

 

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