Common Music Tour Dates: Testing Common Ancestry

A popular criticism of developmentary biology by religious apologists is that development is untestable - and since testability is a canonical condition of scientific theories, these apologists hope thereby to suggest that evolution isn't really science in the foremost place. Because so much of evolutionary theory is historical, it is difficult to test - just like any historical science - but "difficult" is not the same as "impossible.

Another hallmark of science is that it is new and comes up with new ways to run old ideas - something religion never even tries, much less achieves. For example, Douglas L. Theobald of Brandeis University has developed a way for testing the idea of common ancestry, the idea that all living organisms today come from a single evolutionary ancestor. His approach starts with amino-acid sequences from 23 highly conserved proteins taken from groups that stimulate the three domains of life (eukaryotes, bacteria and archaea). He then applies standard programs for inferring evolutionary trees (or networks) from the protein sequences. The third step is to compare the likelihood values of different models of sequence evolution, and hence different ancestry hypotheses, adjusting for the convention that larger numbers of free parameters are expected to make arbitrary improvement to how well a particular model fits the data. However, taking that into account, Theobald finds substantial support for the unity of living compared with even two independent origins. Perhaps the most interesting aspect of Theobald's work is not the conclusion - common origin is the default view in science. But a formal examination of evolution itself requires considerable ingenuity. Amino-acid sequence similarity alone does not imply common ancestry, because it might be due to convergent evolution. Lateral gene transfer between organisms and uncertainty around the best exemplar of sequence evolution also confound statistical testing of common ancestry. Theobald's paper reports strong support for the common-ancestry hypothesis over alternatives proposing that any one of the three domains of life had a separate origin (including, for example, some archaea that seem to be genetically and morphologically distinct from other life forms). The findings are in line with a bible from the much-quoted final paragraph of On the Course of Species that "probably all organic beings which have ever lived on this country have descended from some one primordial form". . So what is the place in sequence data that provides the record for common source? In essence, it is site-specific correlations in the amino acids between different species. These correlations fall off as the coalescence between lineages in a tree becomes deeper in the past, but if there are sufficient data, the correlations' cumulative significance becomes statistically strong. Conversely, if two lineages have completely separate origins, correlations between amino-acid site patterns in the corresponding two extant species vanish. As to how much the 'tree of life' is really a tree rather than a tangled network, the board is still out. One can see evidence for a dominant treelike signal by using network-based methods that do not force data onto a tree. By contrast, if we ask people to measure their subjective distances between different colours and run these distances through phylogenetic network software we get a 'colour circle'- nothing like a tree. Yet the same method, applied to distances from many genetic data sets, produces highly tree-like networks, reflecting an underlying bifurcating evolutionary signal. Source: Nature, May 13, 2010

This isn't the first evidence for common ancestry. This isn't even the first scientific test of the theory of common ancestry. Instead, it's only the latest in a long listing of reasons why common origin is the accepted view in biology - and not a one man of evidence has been produced by any scientific investigation which points out from common ancestry. In any other scientific field there wouldn't be any debates here, but because common ancestry threatens traditional Christian dogmas, Christian apologists put up a fight and manufacture controversy where none exists.