Mixotrophs – An Evolutionary “Nice Try”

Mixotrophs – An Evolutionary “Nice Try”

Amid all the celebration last year over the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of his most famous book, On the Origin of Species,1 I heard little or no mention of how often attempts to explain life’s history from an evolutionary perspective have provided stunning new evidence for creation. One recent example springs from a proposed explanation for life’s remarkable recovery after mass extinction events.

For several decades evolutionists have asserted that mass extinction events were actually less destructive than physicists and geologists claimed. While acknowledging such events did drive many species to extinction, they’ve argued for the likely survival of several members of each order and family. Then, according to the proposed scenario, once conditions on Earth improved, the survivors naturally proliferated and evolved––hence, the mass speciation events observed in the fossil record following each mass extinction.

The latest research, however, paints a different picture.2 First, the debate over what caused the biggest of the mass extinction events—asteroids, volcanoes, wildfires, tsunamis, sea level drops, release of methane from clathrates, anoxic events, or hydrogen sulfide emissions—was finally settled. Sophisticated modeling showed that the impact of a large asteroid (>10 kilometers) crashing into Earth would, in itself, generate most, if not all, of these deadly effects.

A team led by the geophysicist Owen Toon calculated that a large impactor would not only block out the light required for photosynthesis but also generate blinding smoke, dust, and sulfate.3 Animals would be unable to see and even to breathe. In addition, fires would ignite on a global scale and the ocean’s surface water would be globally acidified. Further damage would accrue to coastal regions, struck by tsunamis cresting above 100 meters (330 feet). As Toon’s team concluded, “The combination of all these physical effects would surely represent a devastating stress on the global biosphere.”4

The most devastating of mass extinction events in Earth’s recent history, the Permian-Triassic catastrophe, occurred just 251.4 million years ago and lasted nearly 80,000 years.5 This one disaster resulted in the loss of 96% of all marine species and exterminated nearly every species of land plant, reptile, amphibian, and even insect. A measure of the devastation comes from the “fungal spike” observed at the Permian-Triassic boundary. For a while the fungi population exploded as various fungal species gobbled up the vast quantities of dead vegetation and animal life without restraint from their former competitors, the insects.

Recognition that events such as the Permian-Triassic disaster can exterminate photosynthetic life-forms and wipe out all surface-dwelling animals has caused at least some evolutionists to realize that their models are seriously, if not catastrophically, challenged. So, in the wonderful way science works, researchers have begun looking for natural answers to the challenge.

One research team, a group of British biologists, recently published a paper in which they proposed that “mixotrophs” might have rescued life from these massive extinctions.6

Mixotrophs are organisms with the ability to switch between nutritional sources. They can make their own food through photosynthesis, or they can feed on other life-forms. Thus, when photosynthesis shuts down for whatever reason, mixotrophs can transition to feeding on the decaying remains of dead plants and animals. Later, when the smoke, dust, and sulfate aerosols clear, the mixotrophs can go back to surviving by photosynthesis.

Here’s the proposed scenario in more detail: At least some unicellular and small-bodied mixotrophs somehow survived the mass extinction event, perhaps by being buried in sediments. They lived off dead organic matter until the atmosphere cleared sufficiently, and then returned to photosynthetic activity. Next these mixotrophs rapidly evolved into specialist phototrophs (exclusively photosynthetic organisms) of all types and sizes. The rapid appearance of all these phototrophs then somehow stimulated the equally rapid evolution of the few tiny-bodied animal species that managed to survive the mass extinction event, perhaps through deep hibernation, into a panoply of creatures—all kinds and sizes.

This hypothesis raises a host of new questions and challenges: How many mixotroph species could realistically survive a major extinction event? How rapidly could the survivors evolve into specialized phototrophs? By what means could simple, small-bodied, specialized phototrophs speedily evolve into complex, large-bodied phototrophs? How many tiny-bodied animal species could realistically survive a major extinction event? How could tiny-bodied survivors emerge from deep sleep (or cocoons) and rapidly evolve into complex ecosystems of small- and large-bodied animals?

Given what the fossil record reveals about the speed and diversity with which life proliferates after mass extinction events, researchers should be able to design real-time field experiments capable of answering these questions.

The team of British biologists deserves credit for taking up that challenge—and here are the preliminary results. Initial experiments indicate that some mixotroph species can survive up to a six-month period of intense darkness and then resume photosynthetic activity. As yet, however, experimental conditions fail to approach the full severity and duration a major mass extinction event would engender. Nor have experiments yet addressed the survivability of other plant and animal life-forms. While initial experiments have begun to address survivability questions, none has addressed how the survivors could have evolved fast enough and extensively enough not only to avoid eventual extinction but also to account for prolific speciation. Theoretical speciation models say they could not have, at least not by natural means.7

Future field and laboratory experiments (akin to the Long Term Arbuscular Mycorrhizal Fungi Experiment8and the Long-Term Evolution Experiment9) may soon help settle this creation-evolution question. I remain confident the evidence will point compellingly toward the Creator’s involvement.

  1. Charles Darwin, On the Origin of Species: A Facsimile of the First Edition (Rockville, Maryland: Wildside Press, August, 2003).
  2. Nan Crystal Arens and Ian D. West, “Press-Pulse: a General Theory of Mass Extinctions,” Paleobiology 34 (December 2008): 456-471; wiseGEEK, “What Caused the Permian-Triassic Extinction Event?” (2009): https://www.wisegeek.com/what-was-the-permiantriassic-extinction-event.htm; Lee R. Kump, Alexander Pavlov, and Michael A. Arthur, “Massive Release of Hydrogen Sulfide to the Surface Ocean and Atmosphere During Intervals of Oceanic Anoxia,” Geology 33 (May 2005): 397-400; Michael Gillman and Hilary Erenler, “The Galactic Cycle of Extinction,” International Journal of Astrobiology 7 (January 2008): 17-26; Changqun Cao et al., “Biogeochemical Evidence for Euxinic Oceans and Ecological Disturbance Presaging the End-Permian Mass Extinction Event,” Earth and Planetary Science Letters 281 (May 2009): 188-201.
  3. Owen B. Toon et al., “Environmental Perturbations Caused by the Impacts of Asteroids and Comets,” Reviews of Geophysics 35 (January 1997): 41-78.
  4. Owen B. Toon et al, 41.
  5. Rosalind V. White, “Earth’s Biggest ‘Whodunnit’: Unravelling the Clues in the Case of the End-Permian Mass Extinction,” Philosophical Transactions of the Royal Society of London, Series A 360 (2002): 2963-85.
  6. Harriet Jones et al., “Experiments on Mixotrophic Protists and Catastrophic Darkness,” Astrobiology 9 (July/August 2009): 563-71.
  7. See the review and the original source citations in my book, More Than a Theory (Grand Rapids: Baker, 2009), 149-79.
  8. Gail W. T. Wilson et al., “Soil Aggregation and Carbon Sequestration Are Highly Correlated With the Abundance of Arbuscular Mycorrhizal Fungi: Results From Long-Term Field Experiments,” Ecology Letters 12 (May 2009): 452-61.
  9. Zachary d. Blount, Christina D. Borland, and Richard E. Lenski, “Historical Contingency and the Evolution of a Key Innovation in an Experimental Population of Escherichia coli,” Proceedings of the National Academy of Sciences USA 105 (June 10, 2008): 7899-7906.