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Ignoring Other Research, New Study Explains (Away) the Origin of New Body Plans

Günter Bechly

Body Plans

Every now and then a new scientific paper takes on a particularly daunting challenge. The challenge is to explain the discontinuous origin of new body plans in the history of life on earth, for example, as observed in the sudden appearance of the animal phyla during the Cambrian explosion about 530 million years ago. Most of these attempts fail miserably. That is because the proposed causes are clearly not apt to generate new biologic complexity and diversity. Notorious examples are the slime theory and the oxygen and cancer theories that have already been discussed at Evolution News.

A New Pseudo-Explanation

Recently, a team of British paleontologists added a new pseudo-explanation. Deline et al. (2018) studied the presence and absence of thousands of features from all living animal groups, which allowed them “to create a shape space for animal body plans, quantifying their similarities and differences” (Donoghue in the press release by the University of Bristol 2018). The authors claim: “Our results show that fundamental evolutionary change was not limited to an early burst of evolutionary experimentation. Animal designs have continued to evolve to the present day — not gradually as Darwin predicted — but in fits and starts, episodically through their evolutionary history.”

This is interesting indeed, because it exactly confirms my own argument (Bechly & Meyer 2017) that the history of life is a series of numerous discontinuous abrupt origins (“explosions”), contradicting the fundamental prediction of gradualism implied by Darwin’s theory of evolution through random variation and natural selection. As Richard Dawkins (2009) emphasized in his bestselling book The Greatest Show on Earth: “Evolution not only is a gradual process as a matter of fact; it has to be gradual if it is to do any explanatory work.” Darwin’s theory does not pass this empirical test of its predictions. So far so good (or rather so bad for neo-Darwinism). We already knew this.

Furthermore, the paper states: 

Our results challenge the view that maximum variation was achieved early in animal evolutionary history by nonuniformitarian mechanisms. Rather, they are compatible with the view that the capacity for fundamental innovation is not limited to the early evolutionary history of clades…. Our mapping of metazoan morphospace has shown that, even though some animal phyla demonstrate maximal initial disparity, others, notably chordates, arthropods, annelids, and mollusks, have progressively expanded on the limits of phylum and kingdom level morphospace post-Cambrian.

Thus post-Cambrian evolution has seen body plan innovation, which is hardly controversial. After all, insects, tetrapods, birds, mammals, and other body plans did not exist 530 million years ago. But this point does not negate at all the crucial fact that extreme biological innovation occurred rapidly in the Cambrian. Nor does it negate the fact that when later body plan innovations appear, they typically also do so abruptly.

However, Deline et al. also claim, “The ‘clumpiness’ of morphospace occupation by living clades is a consequence of the extinction of phylogenetic intermediates, indicating that the original distribution of morphologies was more homogeneous.” In a previous article at Evolution News (Anonymous 2018b) this ad hoc hypothesis has already been criticized, because it unashamedly maintains that exactly where the hypothetical intermediates are proposed to have existed, they remain forever inaccessible. How convenient!

An Even More Fundamental Problem

But there is an even more fundamental problem with this new study. As one of their major results, the authors claim that the origin of new body plans did not require the origin of new DNA code for new proteins. Instead, tweaking gene regulatory networks has been a main causal factor in the origin of metazoan disparity. Strangely, the authors completely ignore the work of Paps and Holland (2018) and do not even cite this important paper in their references section. Deline et al. submitted their manuscript on June 26, but the Paps & Holland study was published on April 30, allowing plenty of time to incorporate, or at least to mention those new results, unless these were too inconvenient truths that would have blown their own paper out of the water. 

Paps and Holland reconstructed the ancestral genetic nodes at which different types of animals diverged, and showed that those nodes involved major genetic and genomic innovations compared to other nodes. This clearly refutes one of the major conclusions of Deline et al.’s paper! Thus, Deline et al. are following in the path of Charles Marshall’s failed attempt to downplay the degree of genetic innovation that was necessary in the Cambrian (see Anonymous 2018a). The omission of Paps and Holland gets a truly bizarre twist in the review of Deline et al.’s work by Paps (2018) himself, who praises the new paper to the skies, but does not bother to mention the omission of his own contradicting study. This is a bit fishy.

A Classical Fallacy

The paper also seems to commit the classical fallacy of confusing correlation with causation. It states: “Causal hypotheses of morphologic expansion include time since origination, increases in genome size, protein repertoire, gene family expansion, and gene regulation.” The authors find a correlation with genome size and microRNA repertoire, but no correlation with protein domain diversity, and they conclude that gene regulation was more influential in shaping metazoan disparity. This of course overlooks that the lack of a general correlation between increasing morphological disparity and protein domain diversity does not imply that novel proteins do not play a crucial role in the origin of new body plans, as suggested by Paps and Holland. Apart from that, like all cladistic studies, this paper suffers from the general problem of biased and more or less arbitrary character selection and delimitation (Bechly 2000) in its data for measuring the disparity morphospace in the first place.

Last but not least, the new paper of course does absolutely nothing to explain how on earth random changes in gene regulatory networks could ever produce highly integrated and complex novel organ systems such as arthropod compound eyes, bird feathers, or the countercurrent heat exchange cooling system for the testes in whales. As a causal process, it is as unlikely to generate the phenomenon in question as oxygen levels or cancer.

In short: While certainly an interesting study, Deline et al. delivers just another failed attempt at an explanation for the origin of new body plans and biological disparity. Next?

Literature:

  • Anonymous 2018a. “Groundbreaking Paper Shows Thousands of New Genes Needed for the Origin of Animals.” Evolution News June 7, 2018.
  • Anonymous 2018b. “A Beautiful, Wonderful Solution to the Cambrian Puzzle?” Evolution News, September 7, 2018.
  • Bechly G 2000. “Mainstream Cladistics versus Hennigian Phylogenetic Systematics.” Stuttgarter Beiträge zur Naturkunde Serie A 613, 1–11. (PDF)
  • Bechly G, Meyer S 2017. “The Fossil Record and Universal Common Ancestry.” Chapter 10 in Moreland JP et al. (eds). Theistic Evolution: A Scientific, Philosophical, and Theological Critique. Crossway, Wheaton, pp. 331–362.
  • Deline B, Greenwood JM, Clark JW, Puttick MN, Peterson KJ, Donoghue PCJ 2018. “Evolution of metazoan morphological disparity.” PNAS preprint, September 4, 2018.
  • Paps J 2018. “How animals went from single cells to over 30 different body types.” The Conversation, September 4, 2018.
  • Paps J, Holland PWH 2018. “Reconstruction of the ancestral metazoan genome reveals an increase in genomic novelty.” Nature Communications 9:1730. (PDF)
  • University of Bristol 2018. “Evolutionary origins of animal biodiversity.” Science Daily, September 3, 2018.

Image source: CNX OpenStax [CC BY 4.0 ], via Wikimedia Commons.