Cambrian Explosion Began with Big Brains

Posted on October 11, 2012 in Darwin and Evolution, Dating Methods, Fossils, Marine Biology, Mind and Brain

A fossil Cambrian arthropod shows a large complex brain, prompting evolutionists to propose that evolution ran backwards from there.

Complex brains evolved much earlier than previously thought, 520-million-year-old fossilized arthropod confirms” is how PhysOrg headlined a press release from University of Arizona that found “remarkably well-preserved brain structures” in a fossil from China.  A similar headline is found on Science Daily:  “Cambrian Fossil Pushes Back Evolution of Complex Brains.”  Science Now announced, “Spider ancestor had big brain.”  The press release continued the un-Darwinian refrain:

The remarkably well-preserved fossil of an extinct arthropod shows that anatomically complex brains evolved earlier than previously thought and have changed little over the course of evolution. According to University of Arizona neurobiologist Nicholas Strausfeld, who co-authored the study describing the specimen, the fossil is the earliest known to show a brain.

Cambrian arthropods, including trilobites, clearly had brains, but this one preserved the imprint of soft brain matter so clearly that scientists were able to trace the neural pathways from the brain to the eye stalks.  The press release states that it “represents an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan.”  They must mean “primitive” with respect to age on the evolutionary timeline, else why would a “primitive” animal need a complex brain?  One of the researchers, Nicholas Strausfeld, said, “In principle, Fuxianhuia’s is a very modern brain in an ancient animal.”  Live Science suggested “primitive” equates with “simple” – “The rest of the animal is incredibly simple, so it’s a big surprise to see a brain that is so advanced, as it were, in such a simple animal,” Strausfeld told Live Science.

In the press release, Stausfeld, a neurobiologist at the University of Arizona, made other statements that run counter to evolutionary expectations, even though he assumed the brain evolved:

The fossil supports the idea that once a basic brain design had evolved, it changed little over time, he explained. Instead, peripheral components such as the eyes, the antennae and other appendages, sensory organs, etc., underwent great diversification and specialized in different tasks but all plugged into the same basic circuitry.

It is remarkable how constant the ground pattern of the nervous system has remained for probably more than 550 million years,” Strausfeld added. “The basic organization of the computational circuitry that deals, say, with smelling, appears to be the same as the one that deals with vision, or mechanical sensation.”

Another evolutionary expectation was shattered by this fossil.  Fuxianhuia protensa is a malacostracan, a group with complex brains, including crabs and shrimp.  Evolutionists preferred to believe that insects evolved from simpler-brained branchiopods (including brine shrimp).  The discovery of a complex brain deep in the Cambrian explosion shatters not only that expectation but turns evolution backwards:

Because the brain anatomy of branchiopods is much simpler than that of malacostracans, they have been regarded as the more likely ancestors of the arthropod lineage that would give rise to insects.

However, the discovery of a complex brain anatomy in an otherwise primitive organism such as Fuxianhuia makes this scenario unlikely. “The shape [of the fossilized brain] matches that of a comparable sized modern malacostracan,” the authors write in Nature. They argue the fossil supports the hypothesis that branchiopod brains evolved from a previously complex to a more simple architecture instead of the other way around.

The paper in Nature by Stausfeld, a Londoner and two Chinese colleagues stated that “early-diverging arthropods have scarcely been analysed in the context of nervous system evolution.”  This was, therefore, the first and clearest opportunity to analyze it with Fuxianhuia, “exhibiting the most compelling neuroanatomy known from the Cambrian.”  The authors had to make the astounding claim that later branchiopods underwent an “evolutionary reduction” in brain structure instead of the progressive increase as would have been expected.  “The early origin of sophisticated brains provides a probable driver for versatile visual behaviours, a view that accords with compound eyes from the early Cambrian that were, in size and resolution, equal to those of modern insects and malacostracans,” the abstract stated. (Ma, Hou, Edgecomb and Strausfed, “Complex brain and optic lobes in an early Cambrian arthropod,” Nature 490, 11 Oct 2012, pp. 258–261, doi:10.1038/nature11495.)

However they sliced it, the authors had to conclude that “the brain and optic lobes of Fuxianhuia suggest that the arthropod nervous system acquired complexity by the early Cambrian.”  The editor’s summary of the paper stated again what this fossil means for evolutionary theory:

The Cambrian explosion refers to a time around 530 million years ago, when animals with modern features first appeared in the fossil record. The fossils of Cambrian arthropods reveal sophisticated sense organs such as compound eyes, but other parts of the nervous system are usually lost to decay before fossilization. This paper describes an exquisitely preserved brain in an early arthropod from China, complete with antennal nerves, optic tract and optic neuropils very much like those of modern insects and crustaceans. This suggests that if insects evolved from quite simple creatures such as branchiopod shrimps, then modern branchiopods have undergone a drastic reduction in the complexity of their nervous systems.

The authors found about 50 specimens in various orientations, leading them to infer that “the eye stalk assemblage possessed a considerable degree of rotational freedom and thus allowed active vision”.  The preservation was so remarkable that they were easily able to compare structures with those from living malacostracans, insects and chilopods, each group having a similar tripartite brain.  “Indeed, it is expected that optic lobes would have already evolved sophisticated circuits even more deeply in the arthropod stem-group, enabling high-level visual processing of the kind presumed to be associated with large compound eyes belonging to the stem-group arthropod Anomalocaris.”

Spin Doctoring

In the same issue of Nature, Graham E. Budd tried to rescue evolution from this evidence, using the worn-out cliche that the fossil “may shed new light” on how brain tissues evolved.  His opening paragraph is a masterpiece of spin doctoring, listing various unexpected fossil surprises as triumphs for evolution:

Even to palaeontologists, the fossil record can resemble the chaotic attic of an eccentric relative, stacked with ancient bric-a-brac of dubious usefulness. But the record has recently been throwing up some surprises that are bringing new order to this jumble. Our concept of dinosaurs, for example, has evolved from what were essentially bolted-together lumps of bone into living creatures covered in graceful feathers — and in colour too. Other fossil finds have brought changes to the scale of our understanding of evolution. For example, the discovery of exceptionally well-preserved fossil muscle fibres throughout the record and fossilized embryos from at least the Cambrian period, some 500 million years ago, have provided remarkable insight into the fine-scale evolution of these tissues and life stages. Now, on page 258 of this issue, Ma and colleagues describe preserved nervous tissue from the Cambrian — a find that grants palaeontologists access to the exclusive zoological club of those who study the brain and nervous system.

None of these “surprises” were anticipated by evolutionists, yet Budd described them all as providing “insight into the fine-scale evolution” of life stages.  But clearly, in his own words, the only thing that has “evolved” is their “concept” of how evolution works.  How complex muscle fibers and embryos from the earliest parts of the record could provide “insight” into evolution was left unexplained.  His reference to dinosaurs covered in colorful feathers is also dubious.

From there, Budd disputed the authors’ claim that complex brains appeared early in the arthropod lineage.  His alternative?  “Convergent evolution” (see 10/08/2012) or else a grab bag of rearrangement options:

However, there are two potential alternatives to this far-reaching conclusion. It is possible that the arrangement in Fuxianhuia is convergent to that in the modern crustaceans or insects; in other words, similar brain assemblies to that reported for Fuxianhuia evolved again in later arthropods. Or it may be that we need to rethink the systematic position of Fuxianhuia. That latter option would entail a substantial rearrangement of our present understanding of early arthropod evolution — not least in the highly vexed issue of the ‘great appendage problem’. This refers to the controversial identity of a large anterior appendage found in many Cambrian arthropods, and seemingly also in the Fuxianhuia specimen described here. Discovering which part of the brain this structure is innervated from will add vital information to this debate. Either way, Ma and colleagues’ findings will prompt hasty re-examination of many old specimens, and quite possibly some recasting of recent theories.

(Graham E. Budd, “Palaeontology: Cambrian nervous wrecks,” Nature 490, 11 October 2012, pp. 180–181, doi:10.1038/490180a.)

We want to help our buddy Budd recast some recent theories without having to do any hasty re-examination of old specimens.  Appealing to the fossil evidence, we point out abrupt appearance of all the animal body plans in the Cambrian explosion, with complex brains evident in the early Cambrian and no transitional forms.  From there, diversification and simplification occurs according to built-in variability and adaptation mechanisms, but the original complex designs endure.  This theory of descent is known as intelligent design.  Reference: Darwin’s Dilemma.

 

 

 

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