Monday, April 22, 2013

Mighty mites...or mighty misleading?

The April 11 broadcast of BBC 4's Material World included a discussion of the rapid evolution of mites.  A paper published online on April 8 in Ecology Letters described an experiment in which researchers at the University of Leeds brought soil mites into the lab, put them into 18 test tubes at high population densities, removed 40% of the adults from 6 tubes, 40% of the juveniles from a further 6 test tubes, and didn't harvest any from the remaining tubes.

As described by,
Researchers found significant genetically transmitted changes in laboratory populations of soil mites in just 15 generations, leading to a doubling of the age at which the mites reached adulthood and large changes in population size.
The results have important implications in areas such as disease and pest control, conservation and fisheries management because they demonstrate that evolution can be a game-changer even in the short-term.
Said a post-doctoral collaborator on the project, “The age of maturity of the mites in the tubes doubled over about 15 generations, because they were competing in a different way than they would in the wild. Removing the adults caused them to remain as juveniles even longer because the genetics were responding to the high chance that they were going to die as soon as they matured. When they did eventually mature, they were so enormous they could lay all of their eggs very quickly.”

"Our study proves that the evolution effect--
the change in the underlying biology in
response to the environment--can happen
 at the same time as the ecological
response.  Ecology and evolution are
intertwined," says Tim Benton.
(Credit: University of Leeds, via
Now, the experiment and its results sound interesting.  If the investigators did their genetics right, they showed that a number of genes, 7 of which they said they'd identified, contribute to the life-history change.  So these results might provide worthwhile results in terms of understanding the control of metamorphosis or growth etc. in this species, and probably therefore beyond it.

However, in our view this story totally misrepresented what it had found, in a way that reflects the current mesmerization of science as well as the public, in terms of making huge unwarranted claims and invoking genetic determinism way beyond reason.  Why do we say this?

The author of the study who was interviewed seemed to claim, and the interviewer accepted without question, that his results cast doubt on the central Darwinian tenet that evolution is a very very slow, gradual process.  This is dramatically wrong in at least three respects.

First, this was not natural selection, imposed blindly by the natural ecology of any species, but instead was imposed intentionally from the outside in a way thoroughly controlled by the investigator and made very intense.  It is, in fact, artificial rather than natural selection. Darwin used artificial selection as his model for natural selection, claiming that the same process that farmers and dog or pigeon breeders used to achieve desired states was what occurred in nature, if at a generally invisibly slow pace.

The mite experiment is different from agricultural, orchid, tulip, pigeon race-horse, or pigeon breeding in that the investigators, unlike breeders, apparently didn't specify in advance what trait they were selecting for.  They let the natural genetic variation in their mites determine the responses to the crowding and unnatural dietary conditions.  But the selection was comparably intense (in one experiment, only half the introduced mites survived to reproduce), and intentionally and consistently imposed.

Second, slow gradualism is by all reasonable evidence a typical but not the only way that selection can occur in nature.  Drought, infection and so on can certainly cause rapid evolution in nature.  It just seems to be relatively unusual.  And major changes that Darwin was referring to were those that led to the production of new, complex adaptive traits--like bats flying despite having non-flying mammalian ancestors.  Mite life-span calibration differences are not like that in that there is no reason to think fundamental reorganization was required, or some novel trait.  We have vast amounts of data far more consistent with gradualism as the general pattern than with highly speeded-up adaptation, but even for the latter we have long had theoretical understand of when and how that can occur.  If life is about anything, it's about exceptions rather than rigid rules.

Third, only the most ideological Darwinist these days refuses to recognize that much of evolution occurs without any substantial, much less systematic natural selection.  Genes and the traits to which the contribute can evolve 'neutrally', changing over time just by chance.  So a modern Darwinian has to recognize that the degree of natural selection, and the tightness of adaptation are fluid, variable, and often far less deterministic than Darwin himself seemed generally to believe.   After all, he had vastly less data on time, paleontology, comparative biology, or genetics than we do today.  Anyone who sticks too closely to Darwin's own ideas (and it was the investigator himself who contrasted his results to Darwin), is like someone sticking to the Bible to explain the world:  Darwin was a brilliant world-changing scientist, but he made mistakes and the 150 years since his main work have greatly modified much of what he said. 

Scientists and the journalists who report their work seem simply unable to restrain their exaggeration.  There are many reasons for this, and we're all only human.  But it should be resisted because misrepresentation, intentional or otherwise, or misapplication of theory or even the concept of theory can be very misleading.  We should strive to do better ourselves, and to restrain our own natural tendencies to gild our work and ideas.  It's hard to do, but important.

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