Neural Darwinism, a large scale theory of brain function by
Gerald EdelmanGerald Maurice Edelman is an American biologist who won the 1972 Nobel Prize in Physiology or Medicine for his work 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 PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in 1972 for his work in immunology showing how the population of
lymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with...
s capable of binding to a foreign antigen is increased by differential clonal multiplication following
antigenAn antigen is a substance that prompts the generation of antibodies and can cause an immune response. "Self" antigens are usually tolerated by the immune system; whereas "Non-self" antigens are identified as intruders and attacked by the immune system...
discovery.
Neural Darwinism, a large scale theory of brain function by
Gerald EdelmanGerald Maurice Edelman is an American biologist who won the 1972 Nobel Prize in Physiology or Medicine for his work 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 PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in 1972 for his work in immunology showing how the population of
lymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with...
s capable of binding to a foreign antigen is increased by differential clonal multiplication following
antigenAn antigen is a substance that prompts the generation of antibodies and can cause an immune response. "Self" antigens are usually tolerated by the immune system; whereas "Non-self" antigens are identified as intruders and attacked by the immune system...
discovery. Essentially, this proved that the human body is capable of creating
complex adaptive systemsComplex systems is a scientific field which studies the common properties of systems that are considered fundamentally complex. Such systems are used to model processes in biology, economics, physics and many other fields...
as a result of local events with feedback. Edelman’s interest in selective systems expanded into the fields of neurobiology and
neurophysiologyNeurophysiology 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:
- 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.
- 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. A more correct term would be postpartum period, as it refers to the mother...
behavioral experience through epigenetic modifications in the strength of synaptic connections between neuronal groups. This creates a diverse secondary repertoire by differential amplification.
- Reentrant signaling between neuronal groups allows for spatiotemporal continuity in response to real-world interactions.
Degeneracy
With neuronal heterogeneity (called degeneracy), it is possible to test the many circuits (on the order of 30 billion neurons with an estimated one million billion 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 (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
morphogenesisMorphogenesis , is the biological process that causes an organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation...
. 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
neuriteA 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
efficaciesEfficacy is the capacity to produce an effect. It is used to mean different specific things in different fields.- Healthcare :In a healthcare context, efficacy indicates the capacity for beneficial change of a given intervention Efficacy is the capacity to produce an effect. It is used to mean...
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
plasticityNeuroplasticity is the changing of neurons, the organization of their networks, and their function via new experiences. This idea was first proposed in 1892 by Santiago Ramón y Cajal the proposer of the neuron doctrine though the idea was largely neglected for the next fifty years...
along a fairly quick timetable.
Reentry
The last part of the theory attempts to explain how we experience spatiotemporal consistency in our interaction with environmental stimuli. Edelman 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 HayekFriedrich August von Hayek CH , was an Austrian and British economist and philosopher known for his defense of classical liberalism and free-market capitalism against socialist and collectivist thought. He is considered by some to be one of the most important economists and political philosophers...
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
Daniel DennettDaniel Clement Dennett is a prominent American philosopher whose research centers on 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 the Center for Cognitive...
,
William H. CalvinWilliam H. Calvin, Ph.D., is a 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. SmithLinda 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).
See also
- Anthropic mechanism
- Complex adaptive system
Complex adaptive systems are special cases of complex systems. They are complex in that they are diverse and made up of multiple interconnected elements and adaptive in that they have the capacity to change and learn from experience...
- Darwinism
Darwinism is a term used for various movements or concepts related to ideas of transmutation of species or evolution, including ideas with no connection to the work of Charles Darwin. The meaning of Darwinism has changed over time, and varies depending on who is using the term...
- Evolutionary psychology
Evolutionary psychology attempts to explain psychological traits—such as memory, perception, or language—as adaptations, that is, as the functional products of natural selection or sexual selection. Adaptationist thinking about physiological mechanisms, such as the heart, lungs, and immune system,...
- 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
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 a postulated unit or element of cultural ideas, symbols or practices, and is transmitted from one mind to another through speech, gestures, rituals, or other imitable phenomena...
- Neurodevelopment
- 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
External links
- How Brains Think: Evolving Intelligence, Then and Now by William H. Calvin
- Neurogenesis in the Adult Human Brain
- Johnson, George "Evolution Between the Ears", "New York Times," April 19, 1992, accessed April 16, 2007 (a critical review of Gerald Edelman's 1992 book Brilliant Air, Brilliant Fire)
- Calvin, William "Neural Darwinism: The Theory of Neuronal Group Selection", Science, 24 June 1988, accessed April 16, 2007 (a review of Gerald Edelman's book Neural Darwinism)
- Webpage of Chrisantha Fernando, first author of "Copying and Evolution of Neuronal Topology"
- A Wikiversity course that extensively discusses neural Darwinism
- The basic Neuroscience course at Wikiversity
- The Department of Neuroscience at Wikiversity