South Wairarapa Rebus Club   

The Guest Speaker at our February meeting, after our Annual General Meeting, was Dr Michael Woodhams, a phylogenist, late of the University of Tasmania, Hobart and one of a number of research workers around the world who were exposed to the power of phylogeny and trained to its subtleties at the Allan Wilson Centre at Massey University.

Phylogeny is the evolutionary history of species, or groups of species, with particular reference to the lines of descent and relationships among broad groups of organisms. A diagram of these relationships is often referred to as an “evolutionary tree”. The root is the shared ancestor and branches and twigs are descendant species exhibiting the genetic differences that led to their separation from neighbouring branches. 

Michael illustrated this with an account of a very cunning experiment done by some Australian scientists on a gum tree. They took leaf samples from the ends of eight different branches on the tree and analysed the DNA sequences. In a physical tree, although mutations do not cause the tree to branch, any mutation that occurs after a physical branching has taken place should be apparent in all the descendant cells but not in the cells of other branches. 

Using mutations, identified as changes in the DNA sequence of the bases (A, G, C & T), the researchers examined more than 135,000 different evolutionary trees to determine the most efficient line(s) of descent, the most probable tree(s). Unlike every other evolutionary tree inferred from DNA sequence analysis, in this case the whole history of the evolution being inferred was present physically, as a gum tree! Three “most likely” evolutionary trees were calculated, one of which was congruent with the branches of the gum tree itself and the other two were very close. 

As an example of genetic diversity, in the illustrated tree, the long-lived yellow box, the branch on the left, yielding samples 1, 2 and 3, is genetically resistant to defoliation by so-called Christmas beetles; the rest of the tree is not resistant to this herbivore attack.

In a similar way the evolution (successive mutation) of Polynesian languages can generate an “evolutionary tree” that traces Polynesian exploration and occupation of the Pacific back to Taiwan to find the shared ancestral language.

Before morning tea the club held its AGM, its 4^th as a Rebus Club and its 29^th since it was set up as South Wairarapa Probus Club in 1990. Officers and committee members were elected for the coming year. The quality of the addresses from guest speakers during 2019, each of which was reviewed in this column, was acknowledged. The annual subscription remains at $25.

The South Wairarapa Rebus Club meets in the South Wairarapa Working Men’s Club on the fourth Friday morning of each month. Anyone in the retired age group who may be interested in our Rebus Club is welcome to come along to a meeting as a visitor.  Please contact David Woodhams 306 8319.