Does Evolution need a Rethink?
Ciclid rapid change due to epigenetic phenotypic plasticity
Evolutionary theory, the cornerstone of modern biology, stands as a testament to scientific progress. From Darwin's groundbreaking proposal of natural selection to the Modern Synthesis' integration of genetics, the theory has illuminated the magnificent tapestry of life. Yet, whispers of dissent have emerged, questioning whether this established framework needs a "rethink." The notion of an "Extended Evolutionary Synthesis" (EES) has reignited the debate, prompting us to re-examine the foundation and future of evolutionary thought.
At the heart of the EES lies the proposition that the Modern Synthesis overlooks crucial evolutionary processes. Proponents, led by Laland and colleagues, argue for incorporating mechanisms like niche construction, cultural inheritance, and developmental bias, epigenetics, phenotypic plasticity alongside natural selection. They maintain that the current framework overly emphasizes gene-centricity, neglecting the dynamic interplay between organisms and their environment, cultural transmission, and the inherent biases in developmental systems.
One key argument for the EES centers around niche construction. Organisms actively modify their environment, shaping landscapes and ecosystems that subsequently influence their own evolution.
Beaver dams and bird nests are just a few examples of how this interaction sculpts selective pressures. The EES argues that the Modern Synthesis, by focusing solely on adaptation to pre-existing environments, misses this crucial feedback loop.
Cultural inheritance, the transmission of learned behaviors and acquired traits through social learning, presents another facet of the EES argument.
Birdsong dialects, tool use in primates, and human technological advances are all testament to the power of cultural transmission in shaping populations. While the Modern Synthesis acknowledges cultural evolution, the EES emphasizes its profound impact on selection pressures and evolutionary trajectories.
Furthermore, the EES highlights the influence of developmental bias, the inherent tendencies of organisms to develop along certain pathways due to pre-existing traits and their interactions with the environment.
As well the EES embraces epigenetics and phenotypic plasticity. Like a dimmer switch on your genes, epigenetics fine-tunes how they're used. This dance with environment molds phenotypes - an orchid's vibrant bloom in sun, its pale whisper in shade. Without changing the DNA itself, these chemical tweaks, whispers in the genetic code, empower organisms to wear different hats for different life stages, even across generations. This, the magic of epigenetic phenotypic plasticity, fuels adaptation, resilience, and whispers tales of evolution in action.
However, proponents of the traditional framework argue that the EES, while highlighting potentially valuable aspects, doesn't necessitate a fundamental overhaul. Critics also point to the potential for confusion and redundancy that the EES introduces. They fear overemphasizing non-genetic factors (epigenetics) at the expense of natural selection, the driving force behind the theory.
The debate surrounding the EES is far from settled. Both sides raise valid points, highlighting the complexity and dynamism of evolutionary processes. While a complete overhaul of the Modern Synthesis may not be necessary, the EES can serve as a catalyst for fruitful re-examination and refinement. Integrating novel insights with the established framework can deepen our understanding of evolution, fostering a more holistic and nuanced perspective.
Modern Synthesis (MS) vs. Extended Evolutionary Synthesis (EES)
Emphasis:
MS: Genes, mutation, natural selection as the sole driver of adaptation.
EES: Developmental processes, non-genetic inheritance (epigenetics), niche construction.
Variation:
MS: Random mutations in genes generate all variation.
EES: Developmental bias, epigenetic effects, environmental influences contribute to variation.
Inheritance:
MS: Genes as the sole units of inheritance.
EES: Transmission of acquired traits, parental care, social learning contribute to inheritance.
Change:
MS: Gradual, incremental change driven by selection on existing variation.
EES: Rapid, transformative changes possible through niche construction, developmental thresholds.
Focus:
MS: Individual organisms and competition for resources.
EES: Interactions between organisms, environment, and developmental processes.
Overall:
MS: Strong central framework, limited explanatory power for some phenomena.
EES: Expanding framework, addressing missing pieces, but less defined, more debated.
The EES offers a broader, more nuanced picture of evolution.
Moving forward:
Several key takeaways should guide the discourse:
Emphasize Rethinking: The EES is a call for integration and deeper exploration of existing concepts.
Maintain clarity and communication: Precise use of terminology and clear distinctions between related concepts are crucial to avoid confusion and facilitate productive dialogue within the field.
Embrace ongoing refinement: Evolutionary theory is a living framework, constantly evolving to incorporate new discoveries and insights. The EES debate should be seen as part of this ongoing process of refinement.
Ultimately, the true value of the EES lies not in declaring a need for revolution, but in inspiring a vibrant dialogue that pushes the boundaries of our understanding. By fostering continued exploration and critical examination, both proponents and critics of the EES can contribute to a richer, more comprehensive understanding of the magnificent tapestry of life and its evolution.
Snippets
Does evolutionary theory need a rethink?
Charles Darwin conceived of evolution by natural selection without knowing that genes exist. Now mainstream evolutionary theory has come to focus almost exclusively on genetic inheritance and processes that change gene frequencies.
Yet new data pouring out of adjacent fields are starting to undermine this narrow stance. An alternative vision of evolution is beginning to crystallize, in which the processes by which organisms grow and develop are recognized as causes of evolution.
The number of biologists calling for change in how evolution is conceptualized is growing rapidly. Strong support comes from allied disciplines, particularly developmental biology, but also genomics, epigenetics, ecology and social science. We contend that evolutionary biology needs revision if it is to benefit fully from these other disciplines. The data supporting our position gets stronger every day.
Yet the mere mention of the EES often evokes an emotional, even hostile, reaction among evolutionary biologists. Too often, vital discussions descend into acrimony, with accusations of muddle or misrepresentation.
Perhaps haunted by the specter of intelligent design, evolutionary biologists wish to show a united front to those hostile to science.
We believe that the EES will shed new light on how evolution works.
We hold that organisms are constructed in development, not simply ‘programmed’ to develop by genes. Living things do not evolve to fit into pre-existing environments, but co-construct and coevolve with their environments, in the process changing the structure of ecosystems.
However, another factor is more important: many conventional evolutionary biologists study the processes that we claim are neglected, but they comprehend them very differently (see ‘No, all is well’). This is no storm in an academic tearoom, it is a struggle for the very soul of the discipline.
The core of current evolutionary theory was forged in the 1930s and 1940s. It combined natural selection, genetics and other fields into a consensus about how evolution occurs. This ‘modern synthesis’ allowed the evolutionary process to be described mathematically as frequencies of genetic variants in a population change over time — as, for instance, in the spread of genetic resistance to the myxoma virus in rabbits.
In the decades since, evolutionary biology has incorporated developments consistent with the tenets of the modern synthesis. One such is ‘neutral theory’, which emphasizes random events in evolution. However, standard evolutionary theory (SET) largely retains the same assumptions as the original modern synthesis, which continues to channel how people think about evolution.
The story that SET tells is simple: new variation arises through random genetic mutation; inheritance occurs through DNA; and natural selection is the sole cause of adaptation, the process by which organisms become well-suited to their environments. In this view, the complexity of biological development — the changes that occur as an organism grows and ages — are of secondary, even minor, importance.
In our view, this ‘gene-centric’ focus fails to capture the full gamut of processes that direct evolution.
Missing pieces include how physical development influences the generation of variation (developmental bias); how the environment directly shapes organisms’ traits (plasticity); how organisms modify environments (niche construction); and how organisms transmit more than genes across generations (extra-genetic inheritance). For SET, these phenomena are just outcomes of evolution. For the EES, they are also causes.
There is more to inheritance than genes.
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