Saturday, 7 December 2013

"20 scientific facts seldom taught to students" critically reviewed #8 The evolution of the brain

Collyer’s 8th ‘fact’ is the claim that “each human brain contains about one hundred thousand billion electrical connections (more than can be found in all the world's electrical appliances), a complexity that could not possibly have been produced by chance.” Once again, his ‘fact’ is yet another reflection of his ignorance of practically every facet of the subjects on which he comments:

  • Yet again it is an argument from personal incredulity
  • It shows a considerable ignorance of neurophysiology and neuroscience as these synaptic connections are not ‘programmed’ into the genome, as there are not enough genes in the human genome to specify the formation of the brain down to the last synapse. Synapse formation in fact is being modelled in a Darwinian manner by some neuroscientists.
  • More broadly, Collyer once again forgets that scientists do not believe that complex structures evolved in one step, but did so incrementally over millions of years. Comparative neuroanatomy shows a plausible sequence of simpler brains leading up to the human brain.
 What Collyer forgets here is that no one claims the human brain evolved in one step. Rather, evolution proceeds incrementally from simple brains to more complex ones. Comparative neuroanatomy shows that plausible intermediates exist. [1] Contrary to his assertion, neuroscience does not regard the evolution of the brain as forever beyond evolutionary explanations [2]. Before inventing “facts” such as the alleged impossibility of human brain evolution, Collyer would be well advised to actually speak to neuroanatomists and neurophysiologists and actually learn something about the subject before making ill-informed and baseless arguments.

Lateral views of the brains of a number of extant vertebrate species (the brains are not drawn to the same scale). While there is tremendous variation in both overall brain size (see Fig. 2) and the size of most brain divisions, most vertebrates possess brains that can be divided into the same number of divisions. aob, accessory olfactory bulb (cross-hatched); cb, cerebellum (stippled); ch, cerebral hemispheres (cross-hatched); m, medulla oblongata; ob, olfactory bulb (cross-hatched); ot, optic tectum (black); and p, pituitary gland. Modified from Braun and Northcutt (1999) Integr. Comp. Biol. (2002) 42:743-756

The formation of a complex structure such as the human brain from a simple structure by natural processes is something which happens each time a foetal brain is formed during human embryogenesis. A preformationist argument – one that claims the entire structure of the human brain is completely encoded by the DNA and therefore was programmed by the Creator – is invalidated by modern genomics:

But there is a vexing problem with the notion that the genome provides complete information for the construction of the nervous system of humans and other mammals. It is estimated that just the human neocortex alone has about 1015 (one followed by 15 zeros, or one thousand million million) synapses. Since the human genome has only about 3.5 billion (3.5 x 109) bits of information (nucleotide base pairs), with 30% to 70% of these appearing silent, some neural and molecular scientists have concluded that our genes simply do not have enough storage capacity to specify all of these connections, in addition to including information on the location and type of each neuron plus similar information for the rest of the body.  (Emphasis mine) [3]

As there is not enough room in the genome to encode every synaptic connection, Collyer’s claim that this complex web of neural interconnections was directly created by God is false. Unless Collyer is going to argue that each synaptic connection in the brain during human embryogenesis is the direct result of divine intervention – and that leaves open the vexing problem of what God was doing for infants born with significant neurological disorders – the only reasonable conclusion is that natural processes are responsible for synaptic formation in humans.

A full scientific discussion of these process is well beyond the scope of this article, but it is worth commenting briefly on ‘neural Darwinism’, a theory of brain function advanced by the biologist and Nobel Laureate Gerald Edelman. Inspired by his work in immunology which showed that local events with feedback can create complex systems, Edelman advanced his theory of neuronal group selection to help explain the development and function of the brain:

Like Darwin’s theory of natural selection, the theory of neuronal group selection is based on the continual generation of diversity, with selection occurring at various levels. In the embryonic and maturing brain, variation and selection occur in migrating cellular populations, during cell death, as well as during synapse formation, and both processes are dramatically reflected in enormous synaptic loss. In the mature brain, variation and selection are seen mainly in the differential amplification of synaptic efficacies that result in neuronal group formation, a process that is continually modified by reentrant signaling. Given these population properties and the prevalence of continual variation and selection, the metaphor “neural Darwinism” is not inappropriate. [4]

Edelman’s theory was first advanced in 1978, well before Collyer’s blithe assertion that the brain was too complex to have evolved. His failure to even mention, let alone critique it, once more demonstrates how poorly researched and tendentious his arguments are. Yet again shows how poor the standard of fact checking of science-related articles in The Testimony is.


1. Butler A.B., Hodos W. Comparative Vertebrate Neuroanatomy – Evolution and Adaptation (Wiley-Liss 2005)

2. Striedter G.F Principles of Brain Evolution (Sinauer Associates, 2004)

3. Cziko G Without Miracles. Universal Selection Theory and the Second Darwinian Revolution. (MIT Press, 1995)

4. Edelam GM “Neural Darwinism: Selection and Reentrant Signalling in Higher Brain Function” Neuron (1993) 10:115-125