Reasons to Believe

Modern Brains Emerged in the Cambrian Explosion

The Avalon and Cambrian explosions, events that marked the sudden appearance of myriad complex life-forms, present two of the biggest challenges to the evolutionary theory. Now a new discovery makes the Cambrian explosion an even more profound difficulty for evolutionists to account for.

In examining fossils from this mass speciation event, it was discovered that Cambrian animals not only possessed modern eye designs but also modern brain designs. For decades, the only evidence for ancient brains came from animals preserved in amber, dated no earlier than 230 million years ago. Then in 2008, a team of Chinese paleontologists found components of a central nervous system in shrimp-like fossils extracted from the Chengjiang Cambrian shale deposits. Upon examining these components in 2012, Nicholas Strausfeld, a neuroscientist at the University of Arizona, recognized that they comprised a three-part brain, similar to that found in many arthropod animals today.

Skeptics, however, complained that Strausfeld’s conclusion was based on just one fossil specimen; they expressed doubt that fossil evidence for a brain could be preserved for longer than a half billion years. Two findings addressed these criticisms. The first was the discovery of seven additional specimens revealing evidence for a three-part brain.1 The second was a laboratory experiment demonstrating that the brains of marine worms and terrestrial cockroaches can be preserved indefinitely, if buried under seawater-soaked clay (similar to the soils in the Cambrian fossil beds) that is subjected to gradually increasing pressure.2

Brain Appearance Challenges Evolution

These new findings undermine the idea that arthropod brains evolved slowly into their present modern forms from primitive nerve tissue over 300 million years. Rather, evidence suggests these brains emerged immediately in their modern forms, as seen in the first arthropods that appeared in the Cambrian explosion.

This is not the first time that mass speciation events have presented evolutionary theory with a conundrum. Animal bodies and plans (phyla), including specific features such as skeletons and eyes, appeared suddenly and in a vast array—rather than over a gradual, slow process such as one would expect from unguided evolution.

At the Avalon explosion (575 million years ago), Earth’s population leapt forward from only unicellular life-forms to include animals with body sizes up to two meters across. As soon as the atmospheric oxygen level (increasing from 1 to up to 8 percent) permitted the existence of Avalon animals, they appeared.

Just before the Cambrian explosion (545 million years ago), atmospheric oxygen rose to 10 percent. The resulting alteration in sea chemistry permitted the formation of the first skeletons. The Cambrian saw every known kind of skeleton design appear. In fact, more basic body plans (phyla) were present at the Cambrian explosion than exist today, including 80 percent of all physically and mathematically conceivable skeletal designs.3 

The Cambrian explosion included the sudden appearance of the first animals to feature hard body parts, a mouth, a digestive tract, and eyes. Nearly every eye design that exists today has been found in Cambrian organisms, including compound eyes with numerous hexagonal facets, freely movable eyes on top of both short and long stalks, and inset eyes.4 These multiple eye designs all appear in the fossil record at the same time.

To say that scientists were and still are astounded by the challenge Cambrian fossils pose to evolutionism would be an understatement. For example, evolutionary biologist Gregory Wray wrote:

The Cambrian “explosion” of body plans is perhaps the single most striking feature of the metazoan fossil record. The rapidity with which phyla and classes appeared during the early Paleozoic coupled with much lower rates of appearance for higher taxa since, poses an outstanding problem for macroevolution.5  

A team of evolutionary biologists led by Kevin Peterson concluded:

Elucidating the materialistic basis of the Cambrian explosion has become more elusive, not less, the more we know about the event itself.6

As impossible as it is for evolutionists to explain the sudden arrival of complex skeletons and eyes out of nowhere, they are now faced with another conundrum: the sudden emergence of brains, again out of nowhere. I would argue that the new evidence reveals the handiwork of God as described by the Bible. It appears He wasted no time in filling Earth with complex animals as diverse as physical conditions allowed. As Isaiah declares, “He [God] did not create it [Earth] to be empty; but formed it to be inhabited.”7

Subjects: Cambrian Explosion, Earth/Moon Design

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. Read more about Dr. Hugh Ross.


  1. Xiaoya Ma et al., “Preservational Pathways of Corresponding Brains of a Cambrian Euarthropod,” Current Biology 25 (November 2015): 2969–75.
  2. Gregory D. Edgecombe, Xiaoya Ma, and Nicholas J. Strausfeld, “Unlocking the Early Fossil Record of the Arthropod Central Nervous System,” Philosophical Transactions of the Royal Society B 370 (December 2015): id. 20150038, doi:10.1098/rstb.2015.0038.
  3. R. D. K. Thomas, Rebecca M. Shearman, and Graham W. Stewart, “Evolutionary Exploitation of Design Options by the First Animals with Hard Skeletons,” Science 288 (May 2000): 1239–42.
  4. Xi-guang Zhang and Brian R. Pratt, “The First Stalk-Eyed Phosphatocopine Crustacean from the Lower Cambrian of China,” Current Biology 22 (November 2012): 2149–54; Christopher Castellani et al., “Exceptionally Well-Preserved Isolated Eyes from Cambrian ‘Orsten’ Fossil Assemblages of Sweden,” Paleontology 55 (May 2012): 553–66.
  5. Gregory A. Wray, “Rates of Evolution in Developmental Processes,” American Zoologist 32 (February 1992): 131.
  6. Kevin J. Peterson, Michael R. Dietrich, and Mark A. McPeek, “MicroRNAs and Metazoan Macroevolution: Insights into Canalization, Complexity, and the Cambrian Explosion,” BioEssays 31 (July 2009): 737.
  7. Isaiah 45:18.