Structuralism (biology)

Stuart Kauffman favoured self-organisation, the idea that complex structure emerges holistically and spontaneously from the dynamic interaction of all parts of an organism.

Gerd B. Müller and Stuart A. Newman argued that the appearance in the fossil record of most of the phyla in the Cambrian explosion was "pre-Mendelian"[a] evolution caused by physical factors.

Darwinian biologists have criticised structuralism, emphasising that there is plentiful evidence both that natural selection is effective and, from deep homology, that genes have been involved in shaping organisms throughout evolutionary history.

[6] The philosopher of biology Michael Ruse similarly wrote that Thompson "had little time for natural selection", certainly preferring "mechanical explanations" and possibly straying into vitalism.

He interpreted fossils such as Dickinsonia in the Ediacaran biota as "pneu" structures determined by mechanical inflation like a quilted air mattress, rather than having been driven by natural selection.

[10][11] The mathematical biologist Stuart Kauffman suggested in 1993 that self-organization may play a role alongside natural selection in three areas of evolutionary biology, namely population dynamics, molecular evolution, and morphogenesis.

With respect to molecular biology, Kauffman has been criticised for ignoring the role of energy in driving biochemical reactions in cells, which can fairly be called self-catalysing but which do not simply self-organise.

[15] In 1979, influenced by Seilacher among others, the paleontologist Stephen J. Gould and the population geneticist Richard Lewontin wrote what Wagner called "the most influential structuralist manifesto", "The Spandrels of San Marco and the Panglossian Paradigm".

[17][19] Darwinian biologists freely admit that physical factors such as surface tension can cause self-assembly, but insist that genes play a crucial role.

They note for example that deep homologies between widely separated groups of organisms, such as the signalling pathways and transcription factors of choanoflagellates and metazoans, demonstrate that genes have been involved throughout evolutionary history.

"[15] The evolutionary developmental biologist Lewis Held wrote that "The notion that aspects of anatomy can be explained by physical forces (like expansion cracking) was advocated ~ 100 years earlier in D'Arcy Thompson's 1917 On Growth and Form and in Theodore Cook's 1914 book The Curves of Life.

[d] Over the intervening century, various traits have been proposed to arise mechanically rather than genetically: brain convolutions, cartilage condensations, flower corrugations, tooth cusps, and fish otoliths.

In his 1917 book On Growth and Form , D'Arcy Thompson illustrates the geometric transformation of one fish's body form into another with a 20° shear mapping . He does not discuss the evolutionary causes of such a structural change, and has accordingly been suspected of vitalism . [ 1 ]
Multiple alternatives to Darwinism have been offered since the 19th century to explain how evolution took place, given that many scientists initially objected to natural selection . Many of these theories, including structural or developmental constraints, led (solid blue arrows) to some form of directed evolution ( orthogenesis ), with or without invoking divine control (dotted blue arrows). These theories were largely swept aside by the modern synthesis of genetics and natural selection in the early 20th century (dashed orange arrows). [ 3 ]
Dickinsonia fossil described as a "pneu" structure with chambers inflated like a quilted air mattress . In Adolf Seilacher 's structuralist view, the structure is determined mechanically by the need to distribute the tension across the surface, rather than having been guided by natural selection.
Darwinists and structuralists agree that cell structures like the cell membrane spontaneously self-organize . They disagree on how important self-organization is in other areas of biology.
An ornamented bridge spandrel . Steven J. Gould and Richard Lewontin argued that the triangular area is a byproduct of the adaptation of structures around it.
Natural patterns like those on the skin of the Giant pufferfish can be created by spatial oscillations of chemical signals.
Laurence Moran notes that structuralism focuses mainly on animals , but that animals (emphasized) form only a small portion of the tree of life . [ 15 ]