Neural Darwinism
Neural Darwinism, a large scale theory of brain function by Gerald Edelman
Gerald Edelman
Gerald Maurice Edelman is an American biologist who shared the 1972 Nobel Prize in Physiology or Medicine for work with Rodney Robert Porter on the immune system. Edelman's Nobel Prize-winning research concerned discovery of the structure of antibody molecules...

, was initially published in 1978, in a book called The Mindful Brain (MIT Press). It was extended and published in the 1989 book Neural Darwinism – The Theory of Neuronal Group Selection.

Edelman won the Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 in 1972 for his work in immunology showing how the population of lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

s capable of binding to a foreign antigen is increased by differential clonal multiplication following antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

 discovery. Essentially, this proved that the human body is capable of creating complex adaptive systems
Complex systems
Complex systems present problems in mathematical modelling.The equations from which complex system models are developed generally derive from statistical physics, information theory and non-linear dynamics, and represent organized but unpredictable behaviors of systems of nature that are considered...

 as a result of local events with feedback. Edelman's interest in selective systems expanded into the fields of neurobiology and neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...

, and in Neural Darwinism, Edelman puts forth a theory called "neuronal group selection". It contains three major parts:
  1. Anatomical connectivity in the brain occurs via selective mechanochemical events that take place epigenetically during development. This creates a diverse primary repertoire by differential reproduction.
  2. Once structural diversity is established anatomically, a second selective process occurs during postnatal
    Postnatal is the period beginning immediately after the birth of a child and extending for about six weeks. Another term would be postpartum period, as it refers to the mother...

     behavioral experience through epigenetic modifications in the strength of synaptic
    In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

     connections between neuronal groups. This creates a diverse secondary repertoire by differential amplification.
  3. Reentrant
    Reentry (neural circuitry)
    Reentry is a neural structuring of the brain, specifically in humans, which is hypothesized to allow for widely distributed groups of neurons to achieve integrated and synchronized firing, which is proposed to be a requirement for consciousness, as outlined by Gerald Edelman and Giulio Tononi in...

     signaling between neuronal groups allows for spatiotemporal continuity in response to real-world interactions.


With neuronal heterogeneity (by Edelman called degeneracy), it is possible to test the many circuits (on the order of 30 billion neurons with an estimated one quadrillion connections between them in the human brain) with a diverse set of inputs, to see which neuronal groups respond "appropriately" statistically. Functional "distributed" (widespread) brain circuits thus emerge as a result.

Edelman goes into some detail about how brain development depends on a variety of cell adhesion molecules (CAMs) and substrate adhesion molecules
Substrate adhesion molecules
Substrate adhesion molecules are proteins that attach cells to specific compounds in the extracellular matrix ....

 (SAMs) on cell surfaces which allow cells to dynamically control their intercellular binding properties. This surface modulation allows cell collectives to effectively "signal" as the group aggregates, which helps govern morphogenesis
Morphogenesis , is the biological process that causes an organism to develop its shape...

. So morphology depends on CAM and SAM function. And CAM and SAM function also depend on developing morphology.

Edelman theorized that cell proliferation, cell migration, cell death, neuron arbor distribution, and neurite
A neurite refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture, because it can be difficult to tell axons from dendrites before...

 branching are also governed by similar selective processes.

Synaptic modification

Once the basic variegated anatomical structure of the brain is laid down during early development, it is more or less fixed. But given the numerous and diverse collection of available circuitry, there are bound to be functionally equivalent albeit anatomically non-isomorphic neuronal groups capable of responding to certain sensory input. This creates a competitive environment where circuit groups proficient in their responses to certain inputs are "chosen" through the enhancement of the synaptic efficacies
Efficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...

 of the selected network. This leads to an increased probability that the same network will respond to similar or identical signals at a future time. This occurs through the strengthening of neuron-to-neuron synapses. And these adjustments allow for neural plasticity along a fairly quick timetable.


The last part of the theory attempts to explain how we experience spatiotemporal consistency in our interaction with environmental stimuli. Edelman called it "reentry
Reentry (neural circuitry)
Reentry is a neural structuring of the brain, specifically in humans, which is hypothesized to allow for widely distributed groups of neurons to achieve integrated and synchronized firing, which is proposed to be a requirement for consciousness, as outlined by Gerald Edelman and Giulio Tononi in...

" and proposes a model of reentrant signaling whereby a disjunctive, multimodal sampling of the same stimulus event correlated in time leads to self-organizing intelligence. Put another way, multiple neuronal groups can be used to sample a given stimulus set in parallel and communicate between these disjunctive groups with incurred latency.

Support for the theory

It has been suggested that Friedrich Hayek
Friedrich Hayek
Friedrich August Hayek CH , born in Austria-Hungary as Friedrich August von Hayek, was an economist and philosopher best known for his defense of classical liberalism and free-market capitalism against socialist and collectivist thought...

 had earlier proposed a similar idea in his book The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology, published in 1952 (Herrmann-Pillath, 1992). Other leading proponents include Jean-Pierre Changeux
Jean-Pierre Changeux
Jean-Pierre Changeux is a French neuroscientist known for his research in several fields of biology, from the structure and function of proteins , to the early development of the nervous system up to cognitive functions...

, Daniel Dennett
Daniel Dennett
Daniel Clement Dennett is an American philosopher, writer and cognitive scientist whose research centers on the philosophy of mind, philosophy of science and philosophy of biology, particularly as those fields relate to evolutionary biology and cognitive science. He is currently the Co-director of...

, William H. Calvin
William H. Calvin
William H. Calvin, Ph.D., is an American theoretical neurophysiologist and professor at the University of Washington in Seattle. He is a well-known popularizer of neuroscience and evolutionary biology, including the hybrid of these two fields, neural Darwinism...

, and Linda B. Smith
Linda B. Smith
Linda B. Smith is a Professor of Psychology and Cognitive Science at Indiana University. Smith earned her Ph.D. from the University of Pennsylvania....


Criticism of the theory

Criticism of Neural "Darwinism" was made by Francis Crick who pointed to the absence of replication in the theory, a requirement for natural selection. Recent work has proposed means by which true replication may take place in the brain (Fernando, Karishma & Szathmary, 2008). Furthermore, by adding Hebbian learning to neuronal replicators the power of neuronal evolutionary computation may actually be greater than natural selection in organisms (Fernando, Goldstein & Szathmary, 2010).

See also

  • Anthropic mechanism
  • Complex adaptive system
    Complex adaptive system
    Complex adaptive systems are special cases of complex systems. They are complex in that they are dynamic networks of interactions and relationships not aggregations of static entities...

  • Darwinism
    Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin....

  • Evolutionary psychology
    Evolutionary psychology
    Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...

  • Genetic programming
    Genetic programming
    In artificial intelligence, genetic programming is an evolutionary algorithm-based methodology inspired by biological evolution to find computer programs that perform a user-defined task. It is a specialization of genetic algorithms where each individual is a computer program...

  • Long-term potentiation
    Long-term potentiation
    In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...

  • Meme
    A meme is "an idea, behaviour or style that spreads from person to person within a culture."A meme acts as a unit for carrying cultural ideas, symbols or practices, which can be transmitted from one mind to another through writing, speech, gestures, rituals or other imitable phenomena...

  • Neurodevelopment
  • Psychological nativism
    Psychological nativism
    In the field of psychology, nativism is the view that certain skills or abilities are 'native' or hard wired into the brain at birth. This is in contrast to empiricism, the 'blank slate' or tabula rasa view, which states that the brain has inborn capabilities for learning from the environment but...

  • Society of mind theory
  • Universal Darwinism
    Universal darwinism
    Universal Darwinism refers to a variety of approaches that extend the theory of Darwinism beyond its original domain of biological evolution on Earth...

Further reading

(originally published in Artificial Intelligence
Artificial Intelligence (journal)
Artificial Intelligence is a scientific journal on artificial intelligence research. It was established in 1970 and is published by Elsevier. The journal is abstracted and indexed in Scopus and Science Citation Index. The 2009 Impact Factor for this journal is 3.036 and the 5-Year Impact Factor is...

39 (1989) 121-139.)

External links

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