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Evolution as movement within a ‘fitness landscape’

A third noteworthy way of conceptualising the process of natural selection is in terms of movement within a ‘fitness landscape.’See Kauffman, At Home in the Universe: The Search for Laws of Self-Organization and Complexity 149. The concept of the fitness landscape was first introduced by Sewall Wright in the 1930s and has proven a useful way to visualise how the addition of ‘parameters’ will influence the possible paths of evolution. This in turn can help us apply the abstract idea of evolution to actual biology. The landscape is typically pictured as a mountain range with several peaks of varying height, and valleys in-between. The height at any point on the landscape corresponds to its fitness value; i.e. the higher the point, the greater the fitness of an organism that occupies that spot.

The algorithmic conception makes clear how an organism undergoing Darwinian natural selection will tend to increase its fitness value. When viewed in terms of fitness landscapes it explains how the organism will move ‘up hill.’ As we saw above, an over-simplistic view of natural selection as an algorithm results in the fitness tending to infinity, but when contextualised on a fitness landscape, the possible fitness values are constrained to just those in the terrain; i.e. it can reach the top of a mountain or plateau, but can go no further. Richard Dawkins used the model of fitness landscapes to great effect in his 1996 book Climbing Mount Improbable.Richard Dawkins, Climbing Mount Improbable (New York: W. W. Norton, 1996).

While this conceptual tool adds needed complexity to a model of evolution, it has several limitations. For example, it gives the false impression that the landscape of possible adaptations is fixed. A more realistic representation of the relationship between organisms, environment and fitness would show the landscape changing as a result of the movement (i.e. adaptation) of organisms within it. It also does not make sufficiently clear the influence that adaptations in one organism will have on the fitness landscape of its peers. As Dennett says: “there is a tight interaction between the shape of the fitness landscape and the population that occupies it, creating a series of feedback loops ...The landscape is constantly shifting under your feet.”Dennett, Darwin's Dangerous Idea: Evolution and the Meanings of Life 192-193.

It is also tempting to assume that organisms that reach higher up the tallest peaks are ‘better’ than those lower down or on shorter peaks. Like all models and metaphors fitness landscapes have their limitations. The height of a point on the landscape does not indicate a score of ‘goodness’ or complexity, but solely the fitness of that organism to that local environment.

Importantly, it must be acknowledged that coming up with an objective value for fitness is harder than it may seem. Working from a traditionally Darwinian perspective, we might propose that fitness could be measured in terms of number of progeny produced over unit time, but this is clearly inadequate since it does not consider elephants to be very fit at all. Other possible measures of fitness include: the complexity of individual organisms, the ability to survive in multiple habitats, or to evolve quickly to changing environments, or total biomass, or the ability to respond intelligently to complex problems. Gould is quick to point out that for three out of five of these measures bacteria are superior to humans.

A detailed model of the overall fitness of organisms would probably require several different landscapes, each representing a different aspect of adaptations that influences overall fitness.For more on fitness landscapes see Kauffman, At Home in the Universe: The Search for Laws of Self-Organization and Complexity 57-72.

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Go to Evolution Topic Index

Evolution as movement within a ‘fitness landscape’

[1] Does Evolution ‘do the work of a friend’ for the Christian Religion?
Setting the scene - why focus on providence?
[2] Supposed challenges from the evolutionary sciences to theology
Intellectually fulfilled atheists?
A challenge to human uniqueness and status?
A challenge to purpose in creation?
A threat to the veracity of scripture?
Evolution ‘explains away’ theology?
A challenge to Christian morality?
The challenges in wider context - Darwin as a scapegoat?
[3] The current state of the evolutionary sciences
Different ways of conceptualising Darwinian evolution
Evolution as chance and necessity
Evolution as an algorithm
Ongoing debates: contingency versus convergence
Ongoing debates: what are the key causal factors in biological history?
Ongoing debates: the environment as the principle cause?
Ongoing debates: convergence as the principle cause?
Ongoing debates: ‘Universal biology’ as the principle cause?
The importance of moving from evolution as abstraction to particular history
Ongoing debates: directionality and progress
Ongoing debates: the origin of life
Different levels and kinds of selection?
[4] Responses from theology
Evolution, probabilities and providence
Responses from contemporary theologians
Holmes Rolston III
Keith Ward
John Haught
Arthur Peacocke
An increased role for general providence?
Theology of Creation in the light of evolution: three scenarios
[5] Concluding remarks
Sources

Source:

Adrian Wyard
Adrian M Wyard MSt

See also:

Evolution
The Relation of Science & Religion
Purpose and Design
Genetics
The Argument From Design
The Anthropic Principle
Opinions
Charles Darwin
DNA Double-Helix