Cutting the second slide & Dollo’s “Law”

A recent study on house dust mites has shown that the mighty mites have evolved “in reverse” from an obligate parasite into a free living organism. That is pretty cool. Yet, I find myself in the position once again of questioning the way the research is presented without questioning the quality of the research itself.

For permanent parasites and other symbionts, the most intriguing question is whether these organisms can return to a free-living lifestyle and, thus, escape an evolutionary “dead end.” This question is directly related to Dollo’s law, which stipulates that a complex trait (such as being free living vs. parasitic) cannot re-evolve again in the same form. Here, we present conclusive evidence that house dust mites, a group of medically important free-living organisms, evolved from permanent parasites of warm-blooded vertebrates. – Klimov & O’Connor 2013

The researchers present their result as a refutation of Dollo’s Law, which postulates that evolution is irreversible:

An organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors.

The lifestyle of an obligate parasite severely constrains the evolutionary options of a species. The house dust mite result certainly refutes Dollo’s Law as stated above. While identifying an example of a species evolving to be free living after it’s ancestor evolved from being free living to being an obligate parasite is very interesting, refuting Dollo’s Law itself is not particularly interesting. Furthermore, focusing on that refutation could imply to non-experts that refuting Dollo’s Law is going to cause us to rethink evolutionary theory.

“Dollo’s Law” is a hypothesis proposed in 1893, before a modern understanding of molecular biology, evolutionary biology, or, frankly, probability. The general observation that evolution is highly contingent and that the ease of transitions from one state to another are not equally easy in both directions does make it extremely unlikely that evolution will run in reverse. Unlikely, is not impossible. Unlike the original statement of Dollo’s Law from above, modern biologists understand it as a colorful expression of unlikelihood. I rarely quote Richard Dawkins, but he grasps the point that Dollo’s Law is…

…really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction.

This is the second time in a week I’ve found myself perplexed by the presentation of otherwise quality and interesting work, which has led me to wonder why researchers are trotting out these theoretical straw-men to advertise that their research is interesting, which it is, in its own right.

In my thesis lab, we had a running joke whenever one of us would give a practice talk to the group. Before the presentation would even start, someone would yell:

Cut the second slide!

The first slide is the title slide. As long as this contains your name and a marginally accurate title, it is fine. The next slide starts the introduction and our effort to convince the audience that they want to hear what we are going to say.

This second slide is where things like Dollo’s Law or the “thrifty” genotype hypothesis show up. Typically, these things are not used to indicate the seminar speaker’s research is actually geared toward testing out-dated theories. They serve as keywords – proxies for complex issues – they are not statements of real problems. In sub-fields of biology (I presume it is the same for other sciences), we have sets of straw-man arguments we use to let the crowd know what general sets of problems we are going to be talking about.

In our lab, we forced each other to avoid these cheap tricks that relied on the audience’s shared knowledge base. Instead, we pushed each other to identify the real issues and real motivations behind the research. Not only did that allow us to present our research and its importance (or lack thereof) more accurately, it allowed us to express why we were passionate about what we were doing more authentically.

As Open Access expands, scientists need to become more aware that they are not just writing for the academy, but for the public. If we think everyone has a right to access the fruits of publicly funded research, then we have to face the responsibility that our work will not only be read by people who have the experience and expertise to know what we really mean – ie, cut the second slide.


Author: Josh Witten

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