Friday, November 27, 2009

A Twig on the Evolutionary Tree


Over Thanksgiving daughter Michelle showed me a different, (and new to me) evolutionary tree. We have all seen evolutionary trees. There is one in Darwin's notebooks from 1834.

Some of us are familiar with using DNA to determine parentage of domesticated plants, animals, or indeed children, for example finding the parents of prized wine grapes by sequencing them.

Classic evolutionary trees were drawn by Haechel, and there are several on Wikipedia.

I was surprised to see how different a quantitative tree like the one at right is from a qualitative one or the traditional one from grade school.

The quantitative tree comes from analysis of the 16s rDNA which is an important ribosome enzyme. Its function has been preserved since before the latest common ancestor of all existing plants and animals, and deviations in it provide a measure of evolution.

On this chart one change per base pair is about 8 centimeters along the line.  This is from "Tree of Life" published by Norm Pace in 1997. See this site. Pace is at U of Colorado where Michelle studies.


People are covered under homo as in homo sapiens and are on the bottom hook near the left. We are right next to coprinus, which is a kind of mushroom, and zea which is a family of grasses that includes corn (maize). Other mammal species are going to be even more closely related.

The implication is that a great deal of evolution occurred prior to the differentiation between plants, animals and fungus.



Cynical biologists assert that yeast or oak trees are just as evolved as people, but simply for different things. I say, why not put people on top of the tree? Something has to be on top, and most everyone is going to try to find homo sapiens -- put them on top to make it easy.

The second point is that mammals and "higher" plants are getting a lot of differentiated performance out of some fairly similar genes.

This makes me wonder about saving rain forests for genetic diversity.  There is probably more genetic diversity in pond scum than in a forest of trees.