July 22, 2008 | David F. Coppedge

Mangrove as Metaphor

The mangrove – that shoreline tree with the salt-tolerant roots that grows into dense thickets – is the fulcrum of two unrelated news stories.  It never met a force it couldn’t handle.  It also provides metaphors for evolution and creation.
    PhysOrg reported that the mangrove is a key to saving lives.  “The replanting of mangroves on the coasts of the Philippines could help save many of the lives lost in the 20-30 typhoons that hit the islands annually,” the article said.  Mangrove forests help people in two ways: they create rich ecosystems that benefit local fisheries and the economy, and they absorb the energy of typhoons and tsunamis (02/18/2005).  Tragically, many of the native mangrove forests have been depleted.  In Mexico, National Geographic reported, mangrove forests are being destroyed by resort development.  This is dooming fisheries and ravaging the local economy.  “The government has overvalued such development and grossly undervalued the vital role mangroves play” in the ecology that benefits humans, a report found.  Asian governments are beginning to understand the value of mangroves.  The PhysOrg article showed that expensive rehabilitation projects are not required.  Often, locally-led, low-budget attempts work best.
    On a completely different topic, science writer Carl Zimmer considered the mangrove as one possible metaphor for what has happened to Darwin’s tree of life.  Its appearance of a tangled thicket represents a little closer the kind of relationships among microorganisms that recent research has discerned, contrary to the sketch of a branching tree Darwin produced in his early notebooks.  Writing for Discovery Magazine, in “Festooning the Tree of Life,” Zimmer illustrated concepts from a paper by Tal Dagan (U of Dusseldorf) in PNAS.1  Dagan and colleagues analyzed 181 microbe genomes and determined that lateral gene transfer has been a major contributor to the diversity of microbes.  This means that “much of the history of life may not fit the tree metaphor very well any more,” Zimmer said.
    Zimmer produced a series of illustrations of the original Darwinian branching tree getting all tangled up.  He showed that lateral gene transfer produces cross-connections that scramble the data so thoroughly, the tree pattern is no longer discernible.  After crossing out tree, bush and mangrove thicket, Zimmer selected “Gordian Knot” as the best metaphor for the result.  “This new picture is a far cry from Darwin’s sketch, and thank goodness for that,” he ended.  “A science that doesn’t move forward for 150 years isn’t much of a science at all.  But we may need some new metaphors to help us catch up with it.”

1.  Tal Dagan, Yael Artzy-Randrup, and William Martin, “Modular networks and cumulative impact of lateral transfer in prokaryote genome evolution,” Proceedings of the National Academy of Sciences USA, published online before print July 16, 2008, doi: 10.1073/pnas.0800679105.

Science has moved forward, all right.  It has moved so far forward since Darwin’s time, his speculative worldview of design without a designer has been thoroughly scrambled.  A Gordian knot is not the illustration Darwin projected about how life changes.  Look at Zimmer’s last diagram.  It requires faith to see any tree at all.  Why even maintain the metaphor?  Zimmer’s own reasoning has falsified the original tree diagram and made it superfluous.
    A mangrove thicket, by contrast, is a tightly-knit community of trees, birds, fish, insects and animals all living together simultaneously and harmoniously as a system.  Who really needs to believe they evolved from one another’s microbe ancestors over mythical millions of years?  If you want a worldview that has withstood wave after wave of scientific discoveries, think creation.

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Categories: Genetics

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