The Venus Flytrap: A Major Enigma for Evolution
Among the wonders of the natural world are plants that eat animals, and the best known example is the Venus flytrap Dionaea muscipula. In Charles Darwin’s book on insectivorous plants, he described the plant and its ingenious design in great detail, but did not offer even a clue about its possible evolution (Darwin, 1896, pp. 286-320). He even called the plant “one of the most wonderful plants in the world” (p. 286).
This carnivorous plant is found growing in peaty sandy soil mainly in one small place, the extreme far east coast of North Carolina (Schnell, 2003, p. 85). It catches its prey, mostly ants, beetles, spiders and other crawling arachnids, with a complex, well designed, mitt-shaped trapping mechanism located at the terminal portion of the plant’s leaf (Ellison, 2006; Ellison and Gotelli, 2009).
The trap is triggered by tiny hairs on the mitt’s surface. When an insect or spider brushes against one of its six hairs, the trap closes, but normally only if a different hair is contacted within twenty to forty seconds of the first one (Schnell, 2003, p. 90). The redundant triggering requirement serves as a safeguard against wasting energy due to closing from stimuli such as rain, dust or wind. Truly, this is a finely tuned system.
The Trapping Mechanism
The Venus flytrap is one of a small group of plants capable of rapid response to stimuli, including the legume Mimosa (sensitive plant) which folds its compound leaves inward in response to touch , the legume Desmodium motorium (telegraph plant) which moves small lateral leaflets in order to sample the sun’s intensity so that an associated large leaf can orient itself in the best light, Drosera (sundews) which catch insects with sticky fluid and then bends projecting tentacles around the prey to hold it fast and digest it, and Utricularia (bladderworts) which develop tiny bladders under water. When attached trigger hairs are brushed by a tiny aquatic animal, a trap door swings up and the victim is sucked in by the vacuum in the interior cavity. The trap door snaps shut and the victim is digested.
The trap closing mechanism in Venus flytrap involves a complex interaction between elasticity, turgor, and growth. To help attract prey, the plant’s flytrap secretes sugars and other attractants. In the open, un-tripped state, the trap lobes are convex (bent outwards) but concave (bent inwards) in the closed state, forming a small cavity (Williams, 2002). The complex mechanism and biochemistry used to trigger the rapid closing—about a tenth of a second—is still poorly understood (Sarfati, 2007).
It is known that when the trigger hairs are stimulated, an action potential, mostly involving calcium ions, is generated. A threshold of ion buildup is required for the Venus flytrap to react (Ueda, 2010). To cause rapid closure of their trap walls hydrogen ions are moved into the individual cells, lowering the pH. This causes them to swell rapidly by allowing water to flow into the cells, which changes the trap lobe’s shape, resulting in the trap’s closure.
One extensive Harvard University study of the trapping mechanism concluded the question that motivated Darwin’s life work, namely how did the mechanism evolve, is still unresolved. The study documented that these plants are nature’s ultimate hydraulic engineers (Forterre, et. al, 2005, p. 421).
Proposed Evolutionary History
The carnivorous diet, a very specialized form of feeding, is used by only a very few plant kinds living in soil poor in nutrients. Evolutionists theorize that their carnivorous traps evolved to allow these organisms to survive in harsh environments. The “snap trap” mechanism characteristic of Venus flytrap is shared with only one other carnivorous plant genus, the aquatic and unusual Aldrovanda, a relationship thought by evolutionists to be due to convergent evolution. Another proposal is that both Venus flytrap and Aldrovanda snap traps evolved from a flypaper trap similar to the living Drosera regia.
The model proposes that plant snap-traps evolved from the flypaper traps driven by natural selection for larger prey size, thereby providing the plant with more nutrients. The problem is that large insects can more easily escape the sticky mucilage of flypaper traps. Evolution of the snap-trap mechanism would prevent both escape and kleptoparasitism, theft of captured prey from the plant before it can derive benefits from it. It would also permit a more complete digestion (Gibson and Waller, 2009).
Faster closing allows less reliance on the flypaper model, thus larger insects, instead of flying to the trap, usually walk over to the traps, and are more likely to break free from sticky glands. Therefore, a plant with wider leaves, like Drosera falconeri, is theorized to have evolved a trap design that maximizes its chance of capturing and retaining such prey. Once adequately “wrapped,” escape is far more difficult.
Ultimately, the plant relied more in closing around the insect rather than using stickiness. Thus something like sundew might eventually lose its original function altogether, and in so doing develop the trap “teeth” and trigger hairs, which evolutionists claim are examples of natural selection hijacking pre-existing structures for new functions. At some point in its evolutionary history, the plant would have to develop the complex digestive gland system inside the trap, rather than using dew on the stalks for this purpose, further differentiating it from the Drosera genus.
The theory that Venus flytrap evolved from an ancestral carnivorous plant that used a sticky trap instead of a snap trap seems logical, but is not based on evidence. The theory is the sticky leaf traps consume many smaller, aerial insects, and the Venus flytrap consumes a few larger terrestrial bugs, which then allow it to extract more nutrients from these larger bugs. The claim is this gives Dionaea an advantage over their ancestral sticky trap form (Gibson and Waller, 2009). The problem with this theory is that both plants survive quite well, and both obtain close to the same total amount of needed nutrients. Another problem is the plant would have to, not only evolve the trapping mechanism, but also would have to completely redesign the flypaper system, including loss of the complex adhesive used to trap the insects.
Some molecular evidence indicates a close relationship between snap traps and fly-paper traps (Cameron, et al., 2002, p. 1503). However, evaluation of a few genes, as used in this study, tells us very little about evolutionary relationships. Scores of genes are normally regulated as a set to produce a trait, requiring both comparisons of hundreds of genes as well as comparisons of many plants. This entire account is a just-so story which is not based on fossil or other evidence. The split second nature of the trapping method is too precise to have developed spontaneously.
The major difficulty for evolution is the trap system would not allow for obtaining food until all of the essential parts were functional and in place. It would seem that, given the Venus flytrap’s very short root system, natural selection would select for a much larger and deeper root system rather than evolve an enormously complex trapping system that is still not fully understood today in spite of decades of scientific research.
The total lack of fossil evidence concerning the many steps that would link Venus flytrap and their common ancestor such as Drosera, is explained away by rationalizing that carnivorous plants are generally herbs that do not readily form fossilizable structures, such as thick bark or wood. Therefore, evolutionists must extrapolate an evolutionary history from studies of extant genera (Gibson and Waller, 2009). The problem with this speculation is the soft parts of plants, such as leaves, are very abundant in the fossil record (Zhou, 2003).
A major dilemma for evolution is that the Venus flytrap plant can thrive quite well in its natural habitat of moist peat moss without ever consuming insects. Botanist George Howe regulated their diet by using large glass jars to prevent the plant’s accidental consumption of insects (Howe, 1978, p. 40). Since the plant is able to obtain all of the nutrients it requires from the soil and atmosphere, Charles Darwin’s idea for the natural selection mechanism essential to his concept of evolution is, in this case, based on a totally erroneous foundation. Obviously the Venus flytrap did not evolve, but was beautifully designed for its role in the ecosystem.
Cameron, Kenneth M. et al. 2002. American Journal of Botany, 89(9): 1503–1509.
Darwin, Charles. 1896. Insectivorous Plants. New York: Appleton.
Ellison, Aaron M. 2006. Biology, 8:740–747.
Ellison, Aaron M. and N.J. Gotelli. 2009. Experimental Botany, 60(1):19-42.
Forterre, Yoël et al. 2005. Nature, 433(7024):421-425, January 27.
Gibson, T. C. and D. M. Waller. 2009. New Phytologist, 183(3): 575–587.
Howe, George. 1978. Creation Research Society Quarterly, 15(1):39-40, June.
Sarfati, Jonathan. 2007. Creation, 29(4):36-37, September-November.
Schnell, Donald. 2003. Carnivorous Plants of the United States and Canada. Portland, OR. Timber Press. Second Edition.
Ueda, Minoru. 2010. ChemBioChem. Wiley.
Williams, S. E. 2002. Proceedings of the 4th International Carnivorous Plant Society Conference. Tokyo pp. 77-81.
Zhou, Zhonghe, et al. 2003. Nature. 421: 807-814. February, 20.
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