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This article describes the history of human thinkings on biological evolution and its extensions.
Pre-Darwin
The idea of biological evolution has existed since ancient times, but the modern theory wasn't established until the 18th and 19th centuries, with scientists such as Lamarck and Charles Darwin. Darwin greatly emphasized the difference between his two main inputs: establishing the fact of evolution, and proposing a theory, natural selection, to explain the mechanism of evolution.
Pre-Darwinian evolutionary ideas include Lamarckism and Orthogenesis.
Darwin
While transmutation of species was accepted by a sizeable number of scientists before 1859, it was the publication of Charles Darwin's The Origin of Species which provided the first cogent mechanism by which evolutionary change could persist: his mechanism of natural selection. The evolutionary timeline outlines the major steps of evolution on Earth as expounded by this theory's proponents.
Wilkins identifies Darwin's into seven categories:
- Transmutationism
- Common descent
- Struggle for existence
- Natural selection
- Sexual selection
- Biogeographic distribution
- Heredity
The modern evolutionary synthesis
Main article: Modern evolutionary synthesis
Developments since molecular biology
Following the dawn of molecular biology, it became clear that a major mechanism for variation within a population is the mutagenesis of DNA.
The Williams Revolution
Main article: Williams revolution
"Universal Darwinism"
Daniel Dennett (1995) argues in Darwin's Dangerous Idea that natural selection is an algorithmic process applicable to many circumstances besides biological evolution.
Unconventional extensions to evolutionary ideas
De Chardin's and Huxley's theories
Pierre Teilhard de Chardin and Julian Huxley formulated theories describing the gradual development of the Universe from subatomic particles to human society, considered by Teilhard as the last stage. (see Gaia theory). These are not generally recognized as scientifically rigorous.
Nine levels of development are described in their scheme. Stages one through five are grouped into the Lithosphere, also called Geosphere or Physiosphere, where the evolution of the structure of organisms is ruled by mechanical laws and coincidence. Levels six, seven, and eight are the classical biological stages. Stages six through eight are collectively called the Biosphere, where the progress of the structure of the organisms is ruled by genetic mechanisms. The actual stage, stage 9, is called the Noosphere, where the structure of human society is ruled by psychological, informational and communicative processes.
Recent developments in evolutionary theory
Symbiogenesis
Main article: Symbiogenesis
Another extension to the standard modern synthesis, advocated by Lynn Margulis, is symbiogenesis. Symbiogenesis argues that acquisition and accumulation of random mutations or genetic drift are not sufficient to explain how new inherited variations occur in evolution. This theory states that species arise from the merger of independent organisms through symbiosis. Symbiogenesis emphasizes the impact of co-operation rather than Darwinian competition. This commonly occurs in multigenomic organisms throughout nature.
Neo-structuralist themes in evolutionary theory
In the 1980s and 1990s there was a renewal of structuralist themes in evolutionary biology by biologists such as Brian Goodwin, that incorporates ideas from cybernetics and systems theory, and that emphasizes the role of self-organized processes as being at least as important as the role of natural selection. Some extreme variants consider natural selection as the result of biological evolution and not its cause, though most neo-structuralist biologists would not go this far.
The evolution of altruism
Main article: Altruism
Altruism has been one of the last (and most deeply embedded) thorns in the side of evolutionary theory, but recent developments in game theory have suggested explanations with an evolutionary context. If humans evolved, then so did human minds, and if minds evolved, then so does behaviour - including, according to these models, altruistic tendencies.
Theories of eusociality and the undoubted advantages of kin selection have made good progress in this direction, but they are far from unproblematic. Some writers have pointed out that the conscience is just another aspect of our mental behaviour, and propose an evolutionary explanation for the existence of conscience and therefore altruism. One recent suggestion, expressed most eloquently by the philosopher Daniel Dennett, was initially developed when considering the problem of so-called 'free riders' in the tragedy of the commons, a larger-scale version of the Prisoner's Dilemma.
An interesting example of altruism is found in the cellular slime moulds, such as Dictyostelium mucoroides. These protists live as individual amoebae until starved, at which point they aggregate and form a multicellular fruiting body in which some cells sacrifice themselves to promote the survival of other cells in the fruiting body.