Tag Archives: Common Descent

Do non-coding segments of the genome provide evidence for common ancestry?

From Evolution News.


Darwin’s tree of life might be visible in DNA, if DNA didn’t conspire to scramble the signal.

Now that quite a few genomes have been published, a team from Australia and France went on a Darwin fishing trip in the gene pool. In the largest study of its kind to date, they examined microsatellite markers (tandem-repeated DNA motifs of 1-6 base pairs) that are widespread in eukaryotic genomes. If neo-Darwinism is correct, these non-coding stretches of DNA should reflect the tree of common ancestry by showing similar mutational patterns in related groups.

Well, they don’t. The paper by Meglecz, Neve, Biffin and Gardner in PLoS ONE is titled, “Breakdown of Phylogenetic Signal: A Survey of Microsatellite Densities in 454 Shotgun Sequences from 154 Non Model Eukaryote Species.” What went wrong?

As the title implies, the team checked 154 “non-model” species. Darwinian evolutionists tend to focus on the model species, like a particular roundworm, the fruit fly Drosophila melanogaster, and a species of watercress, because their genomes are complete and most researchers use them in experiments. Problem: they may or may not be representative:

Although information for model species is accumulating rapidly, it is insufficient due to a lack of species depth, thus intragroup variation is necessarily ignored. As such, apparent differences between groups may be overinflated and generalizations cannot be inferred until an analysis of the variation that exists within groupshas been conducted. In this study, we examined microsatellite coverage and motif patterns from 454 shotgun sequences of 154 Eukaryote species from eight distantly related phyla (Cnidaria, Arthropoda, Onychophora, Bryozoa, Mollusca, Echinodermata, Chordata and Streptophyta) to test if a consistent phylogenetic pattern emerges from the microsatellite composition of these species.

Sounds like a good test. After all, scientists shouldn’t generalize on overinflated signals, right? The team expected to find nicely behaved data interpolated between the model species. It wasn’t to be:

It is clear from our results that data from model species provide incomplete information regarding the existing microsatellite variability within the Eukaryotes. A very strong heterogeneity of microsatellite composition was found within most phyla, classes and even orders. Autocorrelation analyses indicated that while microsatellite contents of species within clades more recent than 200 Mya tend to be similar, the autocorrelation breaks down and becomes negative or non-significant with increasing divergence time. Therefore, the age of the taxon seems to be a primary factor in degrading the phylogenetic pattern present among related groups. The most recent classes or orders of Chordates still retain the pattern of their common ancestor. However, within older groups, such as classes of Arthropods, the phylogenetic pattern has been scrambled by the long independent evolution of the lineages.

There are two ways to interpret this anomaly. One is that microsatellites mutate too fast to maintain the phylogenetic signal. (This is known as a “post hoc rationalization.”)

The other is that Darwin was wrong. Data do not show a phylogenetic pattern; they show common design with some variation.

Read the rest here. I’m a skeptic on common ancestry, but not for religious reasons. I just don’t think that it’s compatible with the progress of science.

Is common descent supported by evidence from biogeography?

Just FYI, I am delaying my mean anti-feminist post until 6 PM at least to check it over.

Mysterious Jonathan writing at Uncommon Descent.

Here’s his thesis:

Recently on this blog, I have been exploring and examining some of the genomic arguments for common descent. As I have been documenting in recent weeks, while the case for common ancestry — on the face of it — looks mightily strong, closer inspection reveals that the arguments don’t, in fact, stand up under more rigorous scrutiny. In the vast majority of instances, the corroborative data is very carefully cherry picked from the pertinent data set, and the non-congruent evidence is discarded or ignored.

And here’s a snippet:

One popular argument for common descent is the case from the discipline of biogeography — that is, the study of the geographical and historical distribution of species in relation to one another. The argument is based largely around the observation that species are related in accordance with their geographical proximity with respect to one another.

And here is the problem – this is dynamite:

So, when the biogeographical data does not accord with the predictions and expectations made by common descent, one always has ‘oceanic dispersal’ as an ad hoc fudge factor — including the rather remarkable claim that Monkeys made it across the Atlantic from Africa to South America! As Casey Luskin notes here, molecular studies claim that the South American monkeys diverged from the African monkeys around 35 million years ago. But Africa became an isolated island continent around 80 million years ago!

Apparently, monkeys rode on the back of the Flying Spaghetti Monster from Africa to South America.

I actually thought that the evidence for common descent was fairly good, because Behe accepts it and he is not a Darwinist. I didn’t like it, but facts are facts. But I’m glad that Jonathan is shedding some light on this issue. I would like to be able to argue against it, if the evidence is there.

Assessing the evidence in favor of common ancestry

An article from Evolution News that takes a statement from an evolutionist who supports common descent, and then then refutes it point by point.

Here’s the case for common descent:

UCA is now supported by a wealth of evidence from many independent sources, including: (1) the agreement between phylogeny and biogeography; (2) the correspondence between phylogeny and the palaeontological record; (3) the existence of numerous predicted transitional fossils; (4) the hierarchical classification of morphological characteristics; (5) the marked similarities of biological structures with different functions (that is, homologies); and (6) the congruence of morphological and molecular phylogenies.

(Douglas L. Theobald, “A formal test of the theory of universal common ancestry,” Nature, Vol. 465:219-222 (May 13, 2010).)

And here’s a response to each of those points:

Before I read this post, I only knew about 3, 4, 5 and 6.

I thought that I would post this because I haven’t said much about common descent before. I’m against it.