In the first installment of this series, we encountered the common misconception that the order of the terminal nodes ("tips") on an evolutionary tree reflects the actual relatedness among the species represented. Simply rotating some internal nodes without affecting the branching order ("topology") of the tree -- and thus, making no change to the relationships among species -- showed that that the order of tips on a tree is actually arbitrary. What matters is the way that the species are connected through their common ancestors.

Microbiologist Carl Woese is well known as an iconoclast. Indeed, few biologists have so thoroughly shaken the tree of life as he did when he proposed that there are not two major branches -- prokaryotes, whose cells lack nuclei, and eukaryotes who possess nuclei, including all animals, plants, fungi, and protists -- but rather three. "Prokaryotes", Woese argued, do not represent a cohesive category, and should be split into two deeply divergent lineages: the Bacteria, with which everyone is reasonably familiar, and the Archaea, superficially similar organisms that are less commonly encountered as many of them reside in extreme environments. What's more, studies of genetic data suggested that the Archaea are actually more closely related to eukaryotes -- including humans -- than they are to bacteria.

Woese's three-domain tree of life. From Wikimedia Commons.

At 79 years of age, Woese is still shaking things up. Most recently, he stated in an interview with Wired that,

My feeling is that evolution shouldn't be taught at the lower grades. You don't teach quantum mechanics in the grade schools. One has to be quite educated to work with these concepts; what they pass on as evolution in high schools is nothing but repetitious tripe that teachers don't understand.

The Korean War lasted from June 1950 to July 1953. It served as the basis of the 1968 book MASH: A Novel About Three Army Doctors by Richard Hooker (pen name of former army surgeon H. Richard Hornberger), describing the experiences of surgeons at a Mobile Army Surgical Hospital during the war. This was adapted into a film (MASH) starring Donald Sutherland in 1970, which in turn inspired the TV series M*A*S*H starring Alan Alda.

A single figure graces the pages of Charles Darwin's groundbreaking work On the Origin of Species, first published in 1859. The figure in question depicts a tree-like sequence of branchings through time as hypothetical lineages diverge and new species arise. To be sure, the metaphor of a tree was important in Darwin's thinking about the history of life. He wrote in the Origin,

As large, visually-oriented mammals, we have long had a tendency to consider biological diversity primarily in terms of what we can see. There is, however, an entire world of creatures rarely encountered but no less unique and intriguing for it. Sometimes, one only needs the right tools, or the proper motivation, to recognize a group of organisms well worth our attention.

It is in this spirit that I am pleased to introduce you to Hypsibius dujardini, one of about 700 known species in the Phylum Tardigrada, commonly known as a "water bears" due to their ursine appearance.

It is commonly suggested by anti-evolutionists that recent discoveries of function in non-coding DNA support intelligent design and refute "Darwinism". This misrepresents both the history and the science of this issue. I would like to provide some clarification of both aspects.