Origins of the tree of life

 Darwin is usually credited with being the first person to describe relationships among species as a tree.  I’ll admit I always thought this was the case, until this week when some discussion on an evolution email list I subscribe to enlightened me.

Darwin used this tree figure in The Origin of Species to illustrate his idea of “descent with modification”, with the branches representing the diversity of species all interconnected back through time. 

Darwin's tree of life - the only figure in The Origin of Species.

Darwin's tree of life - the only figure in The Origin of Species.

However, some 50 years earlier, in fact in the year of Darwin’s birth 1809, Jean-Baptiste Lamarck used a tree of sorts to depict evolution in his book Philosophie Zoologique.  Lamarck is best known for wrongly believing that evolution happened by the inheritance of acquired characteristics, but he should be given credit for being the first scientist to develop a theory of evolution – unfortunately he just had the mechanism wrong. 

But ideas about trees were around even before Lamarck’s time.  Perhaps the earliest description of a tree of life comes from Russian naturalist Peter Simon Pallas, in 1766:

But the system of organic bodies is best of all represented by an image of a tree which immediately from the root would lead forth out of the most simple plants and animals a double, variously contiguous animal and vegetable trunk; the first of which would proceed from mollusks to fishes, with a large side branch of insects sent out between these, hence to amphibians and at the farthest tip it would sustain the quadrupeds, but below the quadrupeds it would put forth birds as an equally large side branch.

The earliest published tree diagram likely comes from 1801, when French botanist Augustin Augier published his Arbre Botanique, a detailed tree diagram complete with leaves that depicted his view of the relationships between members of the plant kingdom. 

Arbre Botanique

Of course the theory of evolution has advanced somewhat since Darwin’s time and we now know that the idea of a tree of life is a little too simplistic.  As explained in a recent article in New Scientist (which was published with the outrageously inflammatory cover “Darwin was wrong” that no doubt excited a few creationists), some species relationships, particularly of the earliest organisms, are better described by a network rather than a tree, which acknowledges that hybridisation and horizontal gene transfer play a big role in evolution.

If you want to read more on the history of the tree of life, have a look at this article by David Archibald from San Diego State University.

About these ads

One Response to Origins of the tree of life

  1. david w says:

    Deeply, deeply, geekish confession: I have a T-shirt with Darwin’s ‘first’ tree (http://commons.wikimedia.org/wiki/File:Darwin_tree.png) printed on it in bright red.

    I also found those EvolDir messages interesting, I’d known about Lamarck’s ‘tree’ from SJ Gould but the others were news to me.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

%d bloggers like this: