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Darwin’s Finches: An Icon Gets Retouched


Some scientists at Georgia Tech collected bacteria from a lake near their campus and “helped” them evolve in a test tube. From their results, they made major pronouncements about the tempo and mode of evolution on the faraway Galápagos Islands. For this, they got funding from the National Science Foundation.

That pretty much sums up John Toon’s write-up for the Georgia Tech News Center, “‘First Arrival’ Hypothesis in Darwin’s Finches Gets Some Caveats.”

What exactly do lake bacteria have to do with Darwin’s finches, you ask? Well, the evolutionary scientists wanted to follow up on the famous study by David Lack in 1947. He had proposed a theory about “first arrivals” in a new ecosystem, but his study lacked some important details.

Among his hypotheses was that the birds were successful in their adaptive radiation — the evolutionary diversification of morphological, physiological and behavior traits — because they were early colonizers of the islands. The finches filled the available ecological niches, taking advantage of the resources in ways that limited the ability of later-arriving birds to similarly establish themselves and diversify, he suggested. [Emphasis added.]

If the early bird gets the evolutionary advantage, what happens if the late bird is a better competitor? It changes the iconic story somewhat. “Being first in a new ecosystem provides major advantages for pioneering species, but the benefits may depend on just how competitive later-arriving species are.” The late bird might just peck the lights out of the early bird.

To find out what happens, the Darwin team under Jiaqi Tan put their lake bacteria into test tubes to watch the games play out.

Tan and other researchers in the laboratory of Georgia Tech Professor Lin Jiang tested that hypothesis using P. fluorescens, which rapidly evolves into two general phenotypes differentiated by the ecological niches they adopt in static test tube microcosms.  Within the two major phenotypes — known as “fuzzy spreaders” and “wrinkly spreaders” — there are additional minor variations.

The researchers allowed the bacterium to colonize newly-established microcosms and diversify before introducing competing bacterial species. The six competitors, which varied in their niche and competitive fitness compared to P. fluorescens, were introduced individually and allowed to grow through multiple generations. Their success and level of diversification were measured by placing microcosm samples onto agar plates and counting the number of colonies from each species and sub-species.

Not surprisingly, the results were complicated. The bacteria reproduce much faster than finches, but they reproduce asexually. Their mutation rates are also probably much different. “Still, Jiang and Tan believe their study offers insights into how different species interact in new environments based on historical advantages.”

“If the diversifying species and the competing species are very similar, you can have a strong priority effect in which the first-arriving species can strongly impact the ability of the later species to diversify,” said Jiang, a professor in Georgia Tech’s School of Biological Sciences. “If the species are different enough, then the priority effect is weaker, so there would be less support for the first arrival hypothesis.”

David Lack’s famous book lacked this crucial realization: the first arrival hypothesis works, except when it doesn’t. Evolutionists will now “need to think about the surrounding ecological context of the evolutionary process.”

The paper in Evolution shows that the trajectory of evolution is contingent upon the historical context, which seems to say that anything can happen when the first bird lands on an island:

In the first-arrival hypothesis, David Lack emphasized the importance of species colonization history for adaptive radiation, suggesting that the earlier arrival of a diversifying species would allow it to radiate to a greater extent. Here, we report on the first rigorous experimental test of this hypothesis, using the rapidly evolving bacterium Pseudomonas fluorescens SBW25 and six different bacterial competitors. We show that the earlier arrival of P. fluorescens facilitated its diversification. Nevertheless, significant effects of colonization history, which led to alternative diversification trajectories, were observed only when the competitors shared similar niche and competitive fitness with P. fluorescens. These results highlight the important role of species colonization history, modified by their ecological differences, for adaptive radiation.

Interesting phrase: “alternative diversification trajectories” are possible. The possibility for storytelling just grew exponentially.

It seems unbelievable that nobody performed a rigorous test of David Lack’s hypothesis for seventy years. But it doesn’t matter, because neither study — David Lack’s or Georgia Tech’s –provides any help for Darwinian evolution. The birds hybridize. No origin of species has occurred. The varieties of finches are “trapped in an unpredictable cycle of Sisyphean evolution,” according to McKay and Zink, quoted by Jonathan Wells in his new book Zombie Science (pp. 69-70).

This means that, like the old king Sisyphus of Greek mythology, condemned by the gods to roll a stone up a hill that always escapes and rolls back down, requiring him to repeat the cycle forever, Darwin’s finches are going nowhere.

So here’s what we know in 2017 about Darwin’s finches, one of Jonathan Wells’ original ten Icons of Evolution.

  • Some finches wound up on the Galápagos Islands sometime.
  • Darwin captured some on his visit, but never used them to promote his theory.
  • The finches can freely hybridize.
  • The only major difference between them is the size and shape of the beak.
  • When the weather is dry, bigger-beaked birds do better.
  • When the rain returns, smaller-beaked birds return to previous levels.
  • No speciation has occurred. (This is called “adaptive radiation.”)
  • There exists a nebulous idea called “fitness,” measured by number of offspring.
  • Fitness changes from year to year, as circumstances change.
  • Varieties of finches exchange places as “fittest” from year to year.
  • The first arriver gets priority, unless a fitter bird arrives later.
  • Nobody can know in advance what bird will stay the fittest for how long.
  • The NSF will let you use bacteria as a proxy for birds.

Yes, “Adaptive radiation is an important evolutionary process,” just like the paper begins. Thanks for the money, NSF!

In Zombie Science, Wells points out that in a 1999 pro-evolution booklet for schools, the U.S. National Academy of Sciences called Darwin’s finches “a particularly compelling example of speciation.” He also points out that after 17 years since he exposed the flaws in this evolutionary icon, the “zombie” keeps coming back from the dead, reviving and stalking in biology textbooks. Here, the zombie makes another appearance: research that goes nowhere, proves nothing, and yet pretends that Darwin’s finches, despite “some important caveats,” provide insight into the origin of species.

It’s hard to kill a zombie when the federal government funds its handlers.

Photo: Collecting bacteria from a lake near campus, by Qianna Xu, via Georgia Tech.

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Adaptive RadiationbacteriaDarwin's FinchesevolutionGalápagos IslandsGeorgia TechJiaqi TanJonathan WellsPseudomonas fluorescensZombie Science