Nautilus shells: Irreducibly complex?

CLAIM: Evolution cannot explain the existence of the specialized shells of the nautilus. (Von Vett & Malone, 2017, p.213)

RESPONSE: The chambered shell of the nautilus is not so complicated it could not function if any part were removed, which is the key feature of any biological system claimed to be unable to be produced by evolution (i.e., irreducibly complex). Extensive paleontological evidence and evolutionary biology research provide a comprehensive narrative of the nautilus shell's stepwise development, effectively rendering this argument null.

IRREDUCIBLE COMPLEXITY
Irreducible complexity states that certain biological systems are composed of multiple interdependent parts, all of which are necessary for functionality. The removal of any single component would render the entire system nonfunctional, suggesting that such systems could not have evolved through successive, slight modifications since all parts must be present from the beginning of that system's existence. (Behe, 2006, p.29) Can any parts of the nautilus' shell be removed and the shell still function lacking those parts? Yes!

REDUCING COMPLEXITY
The nautilus' shell is incredibly well designed - it is compact, efficient, and optimized for hydrodynamic buoyancy control by regulating fluids and liquids within its hollow internal chambers (septa). However, these specializations can be shown to be developments on simpler designs, and those simpler designs could function without a variety of pieces present.

- Simplifying the siphuncle: A key feature of the nautilus' buoyancy system is the siphuncle, a tubular structure facilitating the regulation of gas and fluid within its chambers. While it allows for very precise buoyancy adjustments that in turn allow for greater vertical movement and access to diverse ecological niches, it is not necessary to allow for this type of mobility. (Bonacum et al., 2011) Although the siphuncle appeared very early, ancestral forms of nautiloids likely lacked this feature. Early experiments with shell shapes and buoyancy pepper the cephalopod/nautiloid fossil record before the siphuncles' development, with the nautilus' ancestors relying on body positioning and liquid-filled chambers for buoyancy. (Mutvei et al., 2007; Mutvei, 2020) While less efficient, pre-siphuncle cephalopods could rely on a combination of shell morphology, liquid manipulation, and possibly slower movement patterns to navigate. What's more, one study found that even in early siphuncle-equipped cephalopods the siphuncles' size and function varied, indicating that it was experimentally and gradually optimized across time. (Kroger, 2003)

- Simplifying the septa: Modern nautilus shell chambers are divided by 38 septa, though their specialized structure and distribution are not irreducible. More complex septa allow for enhanced resistance to hydrostatic pressure, meaning we should expect nautiloid ancestors to be less optimized for deep water and have fewer septa if they developed gradually - which is exactly what we find. Cephalopods ancestral to nautiloids, such as the Cambrian Plectronocerids, not only exhibit fewer septa that are also relatively basic but were also adapted to simple, shallow marine environments where pressures were lower, and mobility was less demanding, making the adaptations seen in modern nautiluses expected and reducible at the same time. (Lemanis et al., 2016)

- Simplifying the spiral: Lastly, even the shell's spiral shape is not irreducible, but is a built-on adaptation. Earlier cephalopods like Endoceras did not exhibit spiral shells - they had larger, soft body proportions and straight, uncoiled shells. (Peterman et al., 2019) Early nautiloids like the straight-shelled Orthoceras were less efficient, less mobile, less stable, and more vulnerable to predators based on the heavy and conspicuous shape of their shells, meaning that a natural progression away from this design would be expected. That progression is exactly what we see in the fossil record - early nautiloids from the Cambrian and early Ordovician (Plectronoceras and Orthoceras) had long, straight shells, with the later Cyrtoceras beginning to show a gentle curve, genera such as Lituites demonstrating a fairly straight shell with a "tight" coiled section at the end of the straight section, and finally the fully coiled shells seen in the ancestors of the modern nautiluses Allonautilus and Nautlius. (Bonacum et al., 2011; Mutvei et al., 2007; Peterman et al., 2019)

CONCLUSION
While the nautilus shell is an incredibly complex piece of machinery, evolutionary means easily could have produced it. The siphuncle, specialized septa, and curved shell in modern nautiluses can be modified or removed without causing a total loss of function, meaning that the nautilus is not irreducibly complex. Additionally, these features are all specializations on previous nautiloid features and can be seen in the fossil record as emerging in a pattern consistent with evolutionary predictions across time.

REFERENCES AND FURTHER READING

Behe, M. (2006) Darwin's Black Box: The Biochemical Challenge to Evolution. Free Press (2nd ed.).

Bonacum, J., Landman, N. H., Mapes, R., White, M. M., White, A. J., Irlam, J. (2011) Evolutionary Radiation of Present-Day Nautilus and Allonautilus. American Malacological Bulletin, 29(1-2), 77-93.

Kroger, B. (2003) The size of the siphuncle in cephalopod evolution. Senckenbergiana Lethaea, 83, 39-52.



Mutvei, H., Zhang, Y., Dunca, E. (2007) Late Cambrian Plectronocerid Nautiloids and Their Role in Cephalopod Evolution. Palaeontology, 50(6), 1327-1333.

Comments

Post a Comment

Popular posts from this blog

Kent Hovind and The 1879 Brewersville Giant

Image
CLAIM:   In 1879, a 9'8" human skeleton was uncovered from a stone burial mound in Brewersville, Indiana. (Hovind, 2003 , 51:49) RESPONSE:  No physical evidence supports the claim that a nearly ten-foot-tall human skeleton was ever uncovered from a burial mound in Brewersville, Indiana. The earliest mention of this skeleton I could find appears in an anonymous column in the North Vernon Plain Dealer , a local newspaper from North Vernon, Indiana, dated May 22, 1879. (Kell, 2018) The article describes the supposed discovery of a "giant chief" skeleton, measuring at eight feet tall (not ten), dressed in elaborate garments made of mica and "embalmed in charcoal". These descriptions match others commonly reported in numerous sensationalist "giant remains" newspaper articles sparked by the Cardiff Giant hoax of 1869, which had fueled public fascination with tales of prehistoric giants across the United States. (Colavito, 2025) However, these articles w...
Read more

Origins of writing and civilization: Proof of a young Earth?

Image
  CLAIM:  The length of recorded human history is too short for evolutionary timescales. Why did writing and civilization emerge at the same time only in the last few thousand years if humans had been around for hundreds of thousands of years earlier? Did it really take them that long to figure out how to invent writing? This large gap of time is clearly a discrepancy for evolution. (Batten, 2019 ) (Baugh, 1999 , p.120) (Ferrel, 2006 , p.152-156) (Humphreys, 2005 ) (Ham, 2008 , p. 44-46) (Hovind, 2003 , 1:45:29) RESPONSE:  Similar to the young-Earth argument regarding the origin of agriculture , there is no reason to expect the development of writing to occur immediately upon the emergence of anatomically modern humans. The archaeological record clearly demonstrates a prolonged developmental foundation spanning cognitive, cultural, technological, and ecological dimensions that gradually paved the way for behaviorally modern practices like agriculture, civilization, and wr...
Read more

Was Roman Emperor Maximinus Thrax a "giant"?

Image
  Note: This response is taken from a paper published by the author responding to claims made by a poster created by late young-Earth creationist Joe Taylor. The paper in its entirety can be found here . CLAIM:  The Roman Emperor “Maximus” (sic., Maximinus) was 8’6”. ( Hovind , 2003, 51:40) RESPONSE:  As part of an overarching case defending the claim that the Bible makes reference to an extinct race of gigantic humans, Kent Hovind claims that the Roman emperor "Maximus" (whose real name was Maximinus Thrax) was over eight and a half feet tall. While Maximinus Thrax was a real historical figure and was the emperor of Rome from 235-238 CE, he likely was not over eight feet tall.  This claimed height comes from the controversial Historia Augusta , which is estimated to have been written in the fifth century CE (a few hundred years after the death of Thrax), and cites a fictitious source for the height. (Langenfeld, 2017) Thrax's great height and size most likely origin...
Read more