Do New Fossils Soften the Cambrian Explosion?
Look at the picture of fossils in an article on PhysOrg. The discoverers claim these fossils from Gabon are 2.1 billion years old, and provide evidence that multicellular organisms began evolving long before the Cambrian explosion. “Until now, it has been assumed that organized multicellular life appeared around 0.6 billion years ago and that before then the Earth was mainly populated by microbes (viruses, bacteria, parasites, etc.),” the article said. “This new discovery moves the cursor of the origin of multicellular life back by 1.5 billion years and reveals that cells had begun to cooperate with each other to form more complex and larger structures than single-celled organisms.”
The original paper in Nature shows detailed photos of the structures.1 The largest are 12 centimeters long, but most are smaller. Many have a radial growth pattern, and the centers of some show a fold, indicating the organisms were composed of flexible sheets of cells. The fossils, however, show no cellular differentiation, gut, limbs, or other complex structures characteristic of the Cambrian phyla. The best that El Albini et al could claim is that the structures suggest colonies of organisms that were more organized than mere microbial mats. To have grown into such shapes, “They require cell-to-cell signalling and coordinated responses, akin to that required for multicellular organization.” Most of the paper was concerned with how they dated the fossils and ruled out chemical processes for their formation.
In the “News and Views” section of the same issue of Nature,2 Donoghue and Antcliffe (U of Bristol) commented on the findings. They said this find “will get palaeobiologists talking” because there is “excitement” any time fossils bigger than microbes are found before the Cambrian explosion. They began by debunking a myth about Darwin:
It is a peculiar but widely held view that Charles Darwin used the palaeontological record as one of the principal lines of evidence for biological evolution. He did not. To modern eyes, On the Origin of Species presents a shocking account of the fossil record as an archive of evolutionary history.
For instance, Darwin highlights the idea that the then earliest-known fossil-bearing rocks, from the Cambrian period, beginning about 542 million years ago, contain records of modern groups – implying an extensive prehistory teeming with life. One-and-a-half centuries of subsequent research have revealed a vast microscopic fossil record of unicellular protists and bacteria extending, some would argue, as far back as there are sedimentary rocks from which they could be recovered. But although fossils of millimetre- to metre-scale multicellular organisms characterize the 90 million years of the Ediacaran period that precedes the Cambrian, pre-Ediacaran macroscopic fossils are exceedingly rare.
In their timeline of the fossil record, Donoghue and Antcliffe show that the Ediacaran fossils appeared in a mere blip of time before the Cambrian explosion. These, however, are significantly earlier. Darwin knew of no Precambrian fossils. It really bothered him. “It was Darwin’s view that absence of organisms in these early intervals of Earth’s history would prove his theory of biological evolution wrong.” Although they concluded that Darwin would be vindicated now (“The discovery and continuing elucidation of the Precambrian fossil record has met Darwin’s predictions on the extent and structure of evolutionary history”) they also pointed out that “Interpreting truly ancient fossils is an especially tricky business.”
Much of the evolutionary significance of these fossils depends on whether they represent true eukaryotic multicellular life, with division of labor and signalling between the cells. “The fossils are not much to look at,” though, they admitted, and “Out of their geological context, these structures are unremarkable and would probably have been ignored.” Dating of the fossils, therefore, is another requirement for assigning them any evolutionary significance. “The null hypothesis, however, has to be that these remains represent bacterial colonies.” Are they any more significant than stromatolites dated earlier? Do they represent anything as remarkable as the later Ediacaran biota?3
The discoverers ended on a note that stimulates another question. “Although we cannot determine the precise nature and affinities of the 2.1-Gyr macroorganisms from the Francevillian B Formation of Gabon,” they said, “we interpret these fossils as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later.” Combined with Donoghue and Antcliffe’s statement that “pre-Ediacaran macroscopic fossils are exceedingly rare,” this makes one wonder what took evolution so long to do anything with its new experiment in multicellularity. Why did multicellular life expand so rapidly at the Cambrian? Readers should note that all the spectacular evolution of toucans, platypus, dinosaurs, horses and humans occurred in one third of the timeline after the Gabon fossils, assuming the evolutionary dating. If after a century and a half of looking, these rare fossils from one tiny place on the globe are all that paleontologists can find, a statement by Donoghue and Antcliffe in their final paragraph seems understated: “This latest discovery raises more questions than it answers.”
1. El Albani et al, “Large colonial organisms with coordinated growth in oxygenated environments 2.1?Gyr ago,” Nature 466, 100-104 (1 July 2010) | doi:10.1038/nature09166.
2. Philip C. J. Donoghue & Jonathan B. Antcliffe, “Early life: Origins of multicellularity,” Nature 466, 41-42 (1 July 2010) | doi:10.1038/466041a.
3. For background on the Ediacaran biota in relation to the Cambrian explosion, see 12/23/2002, 08/19/2004, 04/23/2006, and 07/14/2009.
Under the most generous concessions to the Darwinists, these fossils can only be described as enigmatic. Under more realistic assumptions, however, they are no help at all. First, consider their rarity. Why isn’t the globe teeming with fossils of multicellular experiments and transitional forms in Precambrian strata? We’re talking about 3.4 billion years of dice-throwing since the first life appeared in their saga. If (as they believe) microbial fossils appeared “as far back as there are sedimentary rocks from which they could be recovered,” evolution had no trouble doing the grunt work of creating cells and spreading them over the globe. Those cells, according to the Darwin fundamentalists, had already mastered genetic coding, transcription, translation, regulation, cell division, signaling and networks run by thousands of molecular machines. Are we to believe that evolution could not do the much easier task of stitching cells together into more complex colonies? Given humans, it’s not hard to envision them forming a club in short order. Given cells with communication tools and remote sensing, it’s also not hard to envision them coming together in social groups, and profiting from division of labor. Coming up with the humans and the cells to begin with is the big leap. Given the explosion of diversity later, why did evolution struggle for most of the habitable history of the planet to cross that threshold?
Second, these fossils are of dubious interpretation. They may be nothing more than fairy-ring colonies growing outward like bacteria in a Petri dish. Perhaps the matlike remains were flexible enough to fold on the inside in some cases. There is no indication of a coelom or tissue differentiation. They do not appear transitional to Ediacaran fossils, let alone to Cambrian animals.
Third, the dating is incestuous to evolutionary geological assumptions. Donoghue and Antcliffe spoke glibly about “speculative hypotheses on the co-evolution of life and the chemistry of the oceans” that tempt them to think the fossils fit “elegantly” within tales of a Great Oxidation Event and other evolutionary sub-myths (12/10/2006). If one does not accept the Darwinian premises, all such talk is circular.
Finally, the structures, even under generous concessions that they represent multicellular experiments far back in the Precambrian, do nothing to mitigate the Cambrian explosion. These fossils have none of the jointed limbs, digestive systems, reproductive systems, eyes, antennae, fins, and other complex organs seen in the earliest animal fossils. As the must-see film Darwin’s Dilemma illustrates powerfully, complex body plans bespeak even more complex developmental programs able to direct cells at the right place at the right time into tissues, organs, and functioning organisms. The only theory that can explain hierarchical organization with goal-directed assembly is intelligent design.
For these reasons, this discovery represents Darwinian wishful thinking. They are grasping at straws, trying to fill a Grand Canyon of a gap in their theory with pebbles. It’s almost humorous watching the tension in their rhetoric between the obligations of scientific restraint and the wish to see a huge embarrassment relieved. “This latest discovery raises more questions than it answers,” they said. One question we’d like to add is, “When are you guys going to concede defeat?”