What is the extended evolutionary synthesis?

The extended evolutionary synthesis (EES) is new a way to think about and understand evolutionary phenomena that differs from the conception that has dominated evolutionary thinking since the 1930s (i.e., the modern synthesis). EES does not replace traditional thinking, but rather can be deployed alongside it to stimulate research in evolutionary biology.

 

 

 

Key concepts

 

The extended evolutionary synthesis emphasizes two key unifying concepts that feature in progressive readings of some sections of the evolutionary biology literature – constructive development and reciprocal causation.

 

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Reciprocal causation

 

Focal topics

 

The extended evolutionary synthesis focuses on insights derived from four research areas that have been subject to alternative interpretations in recent literature, yet nonetheless reveal convergent themes.

 

Developmental bias
Developmental plasticity image alt text
Inclusive inheritance
Niche construction

How the EES differs from the Modern Synthesis

Like the EES, the Modern Synthesis also represents a particular way to understand evolution. It primarily focuses on genes:

 

  • new variation arises through random genetic mutation
  • inheritance occurs through DNA
  • natural selection of genes is the sole cause of adaptation

 

The field of evolutionary biology has evolved, incorporating many new theoretical and empirical findings (e.g. neutral theory, inclusive fitness theory). As a result, today’s evolutionary theory is vastly more sophisticated than the original modern synthesis, which emerged in the 1940s-1960s, and covers a broader range of phenomena. Nonetheless, the most prevalent expectations remain broadly in line with those emphasized by the founders of the modern synthesis, and are distinct from EES predictions:

 

 

Traditional predictions

EES predictions

  1. genetic change causes, and logically precedes, phenotypic change, in adaptive evolutionphenotypic accommodation can precede, rather than follow, genetic change, in adaptive evolution
  2. genetic mutations, and hence novel phenotypes, will be random in direction and typically neutral or slightly disadvantageousnovel phenotypic variants will frequently be directional and functional
  3. repeated evolution in isolated populations is due to convergent selectionrepeated evolution in isolated populations may be due to convergent selection and/or developmental bias
  4. environmental states modified by organisms are not systematically different from environments that change through processes independent of organismal activityniche construction will be systematically biased towards environmental changes that are well suited to the constructor’s phenotype, or that of its descendants, and enhance the constructor’s, or its descendant’s, fitness
  5. parallel evolution explained by convergent environmental conditionsrepeated evolution in isolated population may be due to niche construction
  6. ecosystem stability, productivity and dynamics explained by competition and trophic interactionsecosystem stability, productivity and dynamics critically dependent on niche construction/ecological inheritance
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