Numerous Concepts of the Modern Synthesis and How the Extended Evolutionary Synthesis Explains Them Better


The modern synthesis, which emerged in the mid-20th century, was a landmark achievement in unifying Darwinian evolution with Mendelian genetics. It provided a powerful framework for understanding how life evolves, but like any scientific theory, it has been refined and expanded upon in light of new evidence and discoveries. The extended evolutionary synthesis (EES) is a more recent framework that moves past the MS while incorporating additional mechanisms and processes to explain a wider range of evolutionary phenomena.

Here are 16 concepts associated with the modern synthesis and how the EES sheds new light on them:

1. Variation:

  • Modern Synthesis: Variation arises primarily through random mutations and natural selection in genes.

  • EES: Variation can also arise through epigenetic modifications without changing the DNA sequence, developmental plasticity, and symbiosis.

2. Inheritance:

  • Modern Synthesis: Inheritance is mainly vertical, meaning traits are passed from parent to offspring through discrete units (genes).

  • EES: Inheritance can also be horizontal, involving the transmission of epigenetic modifications, symbionts and transposons.

3. Natural Selection:

  • Modern Synthesis: Natural selection is the primary driver of adaptation, acting on heritable variation to eliminate less fit individuals and favor more fit ones.

  • EES: Natural selection is not required in  processes like phenotypic plasticity, developmental bias, niche construction and epigenetics.

4. Population Genetics:

  • Modern Synthesis: Populations are the units of evolution, and their genetic makeup changes over time through selection, mutation, and gene flow.

  • EES: Populations are open systems that interact with their environment and other populations, and these interactions can influence evolutionary trajectories.

5. Speciation:

  • Modern Synthesis: Speciation typically occurs through geographic isolation and the accumulation of genetic differences between populations.

  • EES: Speciation can also occur through sympatric processes, hybridization, symbiosis and epigenetics.

6. Adaptation:

  • Modern Synthesis: Adaptation is the result of natural selection acting on heritable variation, leading to increased fitness in a particular environment.

  • EES: Adaptation can be facilitated by developmental plasticity, epigenetic modifications, and niche construction, and may not always be the result of natural selection.

7. Macroevolution:

  • Modern Synthesis: Macroevolutionary patterns arise from the accumulation of microevolutionary changes over long periods of time.

  • EES: Macroevolution can also be rapid and punctuated, driven by changes in developmental processes, epigenetics, symbiosis, and environmental catastrophes.

8. Neutral Evolution:

  • Modern Synthesis: Not all evolutionary changes are adaptive; some are neutral and have no impact on fitness.

  • EES: Neutral evolution plays a more significant role than previously thought, and can influence gene frequencies and phenotypic diversity.

9. Developmental Biology:

  • Modern Synthesis: Developmental biology was largely separate from evolutionary biology.

  • EES: Developmental processes (evo-devo) are intimately linked to evolution, and can be crucial for understanding the origin of novel traits and phenotypic plasticity.

10. Symbiosis:

  • Modern Synthesis: Symbiosis was seen as a relatively rare phenomenon with limited evolutionary impact.

  • EES: Symbiosis is widespread and can play a major role in evolution, providing new sources of variation, facilitating adaptation, and driving speciation.

11. Epigenetics:

  • Modern Synthesis: Epigenetics was not well understood and not considered a major factor in evolution. The Weismann barrier specifically rejected “Lamarckian” transgenerational inheritance (TEI).

  • EES: Epigenetic modifications can be heritable (TEI) and influence gene expression, leading to phenotypic variation and potentially driving evolutionary change.

12. Horizontal Gene Transfer:

  • Modern Synthesis: Horizontal gene transfer was thought to be rare and primarily confined to microorganisms.

  • EES: Horizontal gene transfer is more common than previously thought and can play a significant role in evolution, especially in prokaryotes and viruses.

13. Niche Construction:

  • Modern Synthesis: Organisms were seen as passive recipients of selection pressures imposed by the environment.

  • EES: Organisms can actively modify their environment, creating niches that favor their own survival and reproduction.

14. Developmental Bias:

  • Modern Synthesis: Evolution was seen as primarily driven by natural selection acting on random mutations.

  • EES: Developmental processes and epigenetics can inherently bias the direction of evolution, even in the absence of strong selection pressure.

15. Cultural Evolution:

  • Modern Synthesis: Cultural evolution was briefly considered part of the evolutionary framework.

  • EES: Cultural traits can be transmitted and evolve through social learning and imitation, providing a mechanism for rapid adaptation and innovation in humans and other social animals.

16. Evo-Devo:

  • Modern Synthesis: Evolutionary biology and developmental biology were largely separate disciplines.

  • EES: Evo-devo bridges the gap between these two fields, providing insights into how

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