Genomicron: Phylogenetic fallacies: "early branching equals primitive".

Posted 16 April 2008 by PvM

T Ryan Gregory at Genomicron who is an evolutionary biologist specializing in genome size evolution at the University of Guelph in Canada educates us (and perhaps some ID proponents) about some of the common pitfalls in phylogeny. In this case, the posting discusses the findings in a recent paper which argues that the comb jellies and not sponges are the earliest branch. Some have uncritically repeated the LiveScience report "Shock: First animal on Earth was surprisingly complex"

Earth's first animal was the ocean-drifting comb jelly, not the simple sponge, according to a new find that has shocked scientists who didn't imagine the earliest critter could be so complex.

as Ryan points out

This interpretation illustrates a common misconception about evolutionary trees, one that I addressed in a recent paper on the topic (Gregory 2008b). Specifically, it draws the false conclusion that a modern member of an early branching lineage is very similar to the distant ancestor that it shares with other lineages. In actuality, the species under consideration are all modern species whose lineages have been evolving for exactly the same amount of time since their divergence from a common ancestor. The comb jelly lineage may have branched first, but the common ancestor from which it and the other animals lineages diverged probably looked nothing like a comb jelly. It is entirely possible that comb jellies are highly derived (i.e., very different from their early ancestor), just as other animal lineages are.

It should come as no shock to most of us that the LiveScience report was uncritically quoted even though they actual paper and the LiveScience report explains the impact of the findings. Even less of a surprise is that the authors who uncritically quoted the LiveScience report were our idnet.com.au friend at Uncommon Descent as well as Mike Gene at TelicThoughts (also here) and our friend Casey Luskin at EvolutionNews.org What a nice display of "Stupid is as stupid does", these ID proponents read something which appears to contradict earlier science findings, see the word 'complex' and immediately jump to the (wrong) conclusion. Is this the kind of 'science' you want to be taught in schools? Genomicron is an excellent science website and the following papers seem quite interesting. Gregory, T.R. 2008a. Evolution as fact, theory, and path. Evolution: Education and Outreach 1: 46-52. Gregory, T.R. 2008b. Understanding evolutionary trees. Evolution: Education and Outreach 1: 121-137

5 Comments

Nomad · 16 April 2008

Thanks for the info. I read the story on yahoo news (look, I know they're not going to be a great source of science news, but I get it on my cell phone easily and it makes for something good to read when I need to pass some time) and just KNEW that the way it was being reported wasn't telling me everything I needed to know about it, I'm starting to get a feel for when something has been oversimplified to the point that it's no longer useful.

I also knew that the ID crowd would be all over the usage of the term complexity. Like moths to a flame they are inevitably drawn in.

Nigel D · 16 April 2008

This reminds me of something I read a while back, about how evolutionary biologists stopped using the terms "primitive" and "advanced" decades ago because they are so misleading. Every lineage on Earth has the same timespan of evolutionary history behind it.

Thuis story illustrates another common misconception, that as soon as a lineage has diverged from its ancestor, its members are the same as (or closely similar to) their modern descendents. This is obviously nonsense, because the first distinct member of the comb jelly lineage (for example) must have resembled the metazoan common ancestor in many ways, being a recent descendent of it. Early members of a long lineage do not necessarily closely resemble their extant modern descendents.

wamba · 16 April 2008

T Ryan Gregory at Genomicron who is an evolutionary biologist specializing in genome size evolution at the University of Guelph in Canada educates us (and perhaps some ID proponents) about some of the common pitfalls in phylogeny.

Here's some folks who could use some education: The Guelph Creationists

David Stanton · 16 April 2008

Nigel,

The correct terms are basal and derived. The important thing in a tree is not where your branch originated, it is whether you are on a terminal branch and extant or on an interior branch and extinct. The ladder of progress idea went out a long time ago. Why do creationists always argue against 2,000 year old ideas?

Richard · 18 April 2008

You can relate some of these ideas to the evolution of mammals. Monotremes are often referred to as a 'primitive' mammal group because their evolutionary line diverged earliest, but their only notable primitive feature is the fact that they still lay eggs. In respects to other aspects of their morphology, they're really highly derived (bills, quills etc).

By contrast, shrews are a derived mammal group and have a derived reproductive mode, but their general morphology seems to be very conservative.