Primer: ‘Complexity of the Cell’

by TFN

This is Part III in a series of four posts in which TFN Insider had university scientists analyze problematic changes the State Board of Education made to science curriculum standards for Texas public schools in 2009. This year publishers will submit — and the state board will approve or reject — instructional materials based on these flawed standards. The following entry examines the current version of Texas Essential Knowledge and Skills (7)(G), which reads as follows:

(7)  Science concepts. The student knows evolutionary theory is a scientific explanation for the unity and diversity of life. The student is expected to:

(G)  analyze and evaluate scientific explanations concerning the complexity of the cell.

(Other entries in series: TEKS (3)(A) — All Sides of Scientific Evidence; TEKS (7)(B) — Sudden Appearance; TEKS (9)(D) – Self-Replicating Life)


This standard was a new addition to the Texas science TEKS in 2009. It originated at the March 26, 2009, board meeting in an amendment proposed by Don McLeroy, R-Bryan, a self-identified young earth creationist. The original wording of McLeroy’s original amendment was as follows:

(G) analyze and evaluate the sufficiency or insufficiency of natural selection to explain the complexity of the cell.

During the board debate, McLeroy explained that this standard:

“…questions the two key parts of the great claim of evolution, which is [sic] common ancestry by unguided natural processes.”

The board approved McLeroy’s amendment by a vote of 8-6.

The following day (March 27, 2009) Lawrence Allen, D-Houston, moved to strike this standard entirely, and by a vote of 8-7, the board approved his motion. However, Bob Craig, R-Lubbock, immediately proposed “compromise” language for this standard that was approved by a vote of 13-2. This compromise language was the final version adopted by the board.

Scientific and Pedagogical Problems with Standard

By Dr. John Wise, Research Associate Professor of Biological Sciences and Adjunct Associate Professor of Biological Sciences at Southern Methodist University in Dallas

The language of this standard comes directly out of the intelligent design/creationism movement and represents  discredited and scientifically falsified hypotheses. The expectation that students are required to “analyze and evaluate scientific explanations concerning the complexity of the cell” potentially opens the classroom and textbooks to discussions of thoroughly refuted creationist claims of the “irreducible complexity” of the cell’s components, an idea most recently popularized by Discovery Institute Fellow Michael Behe.

Behe was the primary witness for the defense in the 2005 Dover intelligent design trial, which ruled that intelligent design is simply creationism relabeled.1 The cross examination of Behe by the plaintiffs’ attorney during this trial provides an important context for the appearance of the phrase “complexity of the cell” in the Texas science standards.2 During the trial Behe testified that there were no explanations in the scientifically peer-reviewed literature that could explain how random mutation and natural selection, the cornerstones of evolutionary theory, could build a complex system. Unfortunately for the intelligent design creationist movement, however, this claim was patently proven false during cross examination. For a short and non-exhaustive listing of the scientifically falsified claims of Behe’s “irreducible complexity” hypothesis, including examples for the eukaryotic cilium, bacterial flagellum, blood clotting cascade, and the mammalian immune system, see endnotes 3,4. Mechanisms for the evolution of biological complexity by fully naturalistic, evolutionary mechanism have been postulated and are supported by experimental, observational and inferential evidence. (See endnote 5 for a survey article.) These mechanisms include the incremental additions model, the scaffolding model, the co-option model and the emerging complexity model.

Good science education in general – and the writing of good science textbooks in particular – requires that the educator and author select hypotheses that are well supported by experimental and observational evidence. Any examples utilized as a part of this instruction should focus on successful scientific analyses of natural phenomena to explain particular details about the natural world and how it works. To allow the incorporation of falsified hypotheses such as those of Michael Behe’s “irreducible complexity” hypothesis into the Texas public school curricula and textbooks, for any reason other than as examples of bad scientific thought that has been conclusively rejected, does an injustice to our children. The time allotted for our students to learn real science is preciously short and should not be diluted with falsified information from nonscientific, intelligent design/creationist sources.

How Publishers Can Responsibly Address Standard
By Dr. Ben  Pierce, Professor of Biology and holder of the Lillian Nelson Pratt Chair at Southwestern University in Georgetown

This standard requires that students analyze scientific explanations concerning the complexity of the cell—it does not require that publishers introduce nonscientific explanations, such as intelligent design arguments that complex cells can only be explained by invoking an intelligent designer.

Although “complexity” is not defined in this standard, it is often interpreted in terms of the number of parts, number of genes, number of interactions between parts, or number of hierarchical levels. Publishers can discuss the scientific evidence for the evolution of cellular complexity, which is extensive and comes from a number of sources, including physical, biochemical, cellular, DNA, and fossil evidence.6,7 Scientific understanding of key steps in the evolution of cellular complexity has been greatly facilitated in recent years by progress in reconstructing the tree of life, which consists of the evolutionary branching patterns among all living organisms.8 Fossil evidence has also played an important role, providing calibration for events inferred by evolutionary trees, as well as independent verification of conclusions based on the evolutionary trees.

One of the most important steps in evolution of cellular complexity is the evolution of eukaryotic cells, which possess nuclear membranes and membrane-bound organelles lacking in simpler prokaryotic cells. One way that publishers can meet standard (7)(G) is by discussing scientific evidence for this key evolutionary transition.  Much evidence supports the idea that eukaryotic organelles originated from free-living bacteria that were ingested by early cells and lived inside the cell as endosymbionts. This idea, called the endosymbiotic theory, proposes that the endosymbionts eventually evolved into chloroplasts, mitochondria, and perhaps even nuclear membranes.9 The endosymbiotic theory is supported by considerable biochemical, cellular, and genetic data.10 Other studies provide scientific explanations for how the first cells evolved.11,12

Although creationists often argue that evolution cannot explain complex cellular structures, the ability of natural selection and other evolutionary forces to generate complex adaptive features has been demonstrated theoretically,13,14, by computer simulation15, and in the laboratory.16 For example, a recent study demonstrated through ancestral gene reconstruction how the functional integration between a hormone and hormone receptor evolved through the process of Darwinian evolution17.


1 See Judge John Jones, III decision: (accessed February 18, 2011).
2 See, and especially for transcripts of the cross-examination of Behe. The latter concentrates on Behe’s irreducible complexity claim. (accessed February 18, 2011).
3 See Niall Shanks and Karl Joplin. 2000. Reports of the National Center for Science Education 20 (1-2) 25-30. (accessed Feb. 18, 2011).
4 See “Big Problems with Intelligent Design” website at (accessed Feb. 19, 2011).
5 Pond, Finn. 2006. Reports of the National Center for Science Education 26 (3) 22, 27-31. (accessed Feb. 19, 2011).
6 Cavalier-Smith, T.  2006.  “Cell evolution and Earth history: stasis and revolution.”  Philosophical Transactions of the Royal Society B 361:969-1006.
7 Woese, C. R.  2002.  “On the evolution of cells.” Proceedings of the National Academy of Science 99:8742-8747.
8 See (Accessed March 2, 2011).
9 Margulis, L.  1970.  Origin of Eukaryotic Cells.  Yale University Press, New Haven.
10 Futuyma, D. J.  2009.  Evolution, 2nd Edition.  Sinauer Associates, Sunderland, MA.
11 Sole, R. V.  2008.  “Evolution and self-assembly of protocells.” The International Journal of Biochemistry and Cell Biology 41:274-284.
12 Martin, W. and M. J. Russell.  2011.  “On the origin of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells.” Philosophical Transactions of the Royal Society B 358:59-85.
13 Fisher, R. A.  1930. Genetical History of Natural Selection.  Oxford University Press, Oxford.
14 Force, A. et al.  2005. “The origin of subfunctions and modular gene regulation.” Genetics 170: 433–446.
15 Lenski, R. E.  et al.  2003.  “The evolutionary origin of complex features.” Nature 423: 139-144.
16 Elana, S. F. and R. E. Lenski.  2003.  “Microbial genetics: Evolution experiments with microorganisms: the dynamics and genetic bases of adaptation.” Nature Reviews Genetics 4: 457-469.
17 Bridgham et al.  2006. “Evolution of hormone-receptor complexity by molecular exploitation.” Science 312:97-101.