Origins of the tree of life (re-post)

August 27, 2010
The chicken or egg blog family is on holiday in Germany during August, so I probably won’t have a chance to write any new posts.  To keep you all entertained, I’ll be re-posting some of my earlier (pre-Sciblogs) articles. This post is from August 2009.

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.

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.


Tuatara: one species or two? (re-post)

August 21, 2010
The chicken or egg blog family is on holiday in Germany during August, so I probably won’t have a chance to write any new posts.  To keep you all entertained, I’ll be re-posting some of my earlier (pre-Sciblogs) articles. This post was written in July 2009.

New Zealand’s most iconic reptile, the tuatara, is currently regarded as two separate species – Sphenodon guntheri, which is found naturally only on North Brother Island in Cook Strait, and Sphenodon punctatus, which are found on other islands in Cook Strait and off the north-east coast of the North Island.  However research just published online in Conservation Genetics shows that Sphenodon guntheri is not as genetically distinctive as first thought, and suggests tuatara should be regarded as one species.  Read the rest of this entry »

Chemical attraction? (re-post)

August 12, 2010

The chicken or egg blog family is on holiday in Germany during August, so I probably won’t have a chance to write any new posts.  To keep you all entertained, I’ll be re-posting some of my earlier (pre-Sciblogs) articles.  This one is the very first post I wrote for this blog, from March 2009.

Research published in last month’s Chemistry and Biodiversity journal heralded the discovery of a new compound “tuataric acid”. Yes, isolated from our very own tuatara.

Stefan Schulz and his colleagues at University of Braunschweig, and collaborator Paul Weldon at the Smithsonian Institution, have analysed the constituents of the cloacal secretions in tuatara and found an unexpectedly diverse array of compounds. As tuatara have no external sexual organs, the cloaca is the “one stop shop” opening at their posterior end, with prominent skin glands on either side of the opening that secrete a greasy white substance. When the tuatara secretions were analysed, Schulz and colleagues found over 150 different types of glyceride-based molecules, including one never-before seen compound, which they dubbed “tuataric acid”.
Read the rest of this entry »


Human handedness – inherited or developed?

August 3, 2010

This post is a little off the topic of what I normally write about, but its something I’ve been wondering about lately as the little munchkin grows up. She’s 6 months old now and is starting to use her hands a lot, going through that grabby stage where anything within arms length is grabbed and shoved in the mouth.  I’ve noticed that more often than not she’s using her left hand for this exploring.  It’s her left hand that grabs her left foot, and her left hand that grabs the spoon during my attempts to introduce her to the wonderful world of solid food.

Does this mean she’s going to be left-handed?  Coming from an extended family of determinedly right-handed people this comes as a bit of a surprise, and makes me wonder if there is an inherited component to handedness, or if there is some trigger during development that makes babies favour one hand over the other. Read the rest of this entry »