Unveiling the Hidden Evolution: Genetic Assimilation and the Macroevolution Paradox

The article "Perspective: Genetic Assimilation and a Possible Evolutionary Paradox: Can Macroevolution Sometimes Be So Fast As To Pass Us By?" by Pigliucci et al. delves into a fascinating concept: genetic assimilation. This process challenges our traditional understanding of evolution by suggesting that significant evolutionary change can occur surprisingly quickly, potentially escaping our observation.

The Core Mechanism and its Controversial Past

Genetic assimilation proposes that environmental pressures can induce epigenetic phenotypic changes in an organism. These changes, initially triggered by the environment, can become genetically encoded over generations. This means the organism evolves to express the previously environmentally induced trait even without the original environmental pressure.

The authors delve into the historical acceptance and rejection of genetic assimilation within evolutionary biology. The concept was first proposed by C.H. Waddington in the 1940s and gained traction for a time. However, during the "hardening" of the neo-Darwinian synthesis, genetic assimilation faced criticism for potentially undermining the role of natural selection. This led to a decline in its popularity for several decades. However, the article argues for a reevaluation of genetic assimilation in light of its potential to explain rapid evolutionary change in the light of the recent discovery of epigenetics.

The Paradox: Speeding Past Our Observations

The intriguing aspect of genetic assimilation lies in its potential speed. The authors argue that genetic assimilation can occur within a relatively short timeframe, just a few generations. This poses a challenge to our traditional methods of studying evolution, which often rely on broad comparative studies across vast stretches of time.

Imagine an organism exposed to a new environment (perhaps due to climate change or habitat destruction). This environment triggers a beneficial epigenetic phenotypic change, say thicker fur for colder temperatures. 

Sheep Fur thickness due to epigenetics

Through genetic assimilation, this change becomes heritable within a few generations. However, researchers focusing on the broader evolutionary history of the species, say by studying fossils millions of years old, might miss this rapid adaptation because it happened within a relatively short window.

New Research Strategies to Catch a Moving Target

Pigliucci et al. propose a shift in research focus to address this potential "blind spot" in our understanding of evolution. They advocate for a two-pronged approach:

1. Historically Informed Research: By studying closely related populations or recently diverged species, researchers can potentially detect the footprints of recent genetic assimilation. These closely related groups offer a more nuanced picture of evolutionary change within a shorter timeframe. For instance, comparing populations of a butterfly species that recently colonized a new island habitat with those on the mainland could reveal rapid adaptations driven by genetic assimilation and epigenetics.

Butterfly wing colors due to epigenetics

2. Focusing on Intraspecific Phylogenies: Traditionally, phylogenetic studies focus on higher taxonomic levels (families, orders). These studies aim to reconstruct the evolutionary relationships between different species. The authors suggest delving deeper into intraspecific phylogenies, the evolutionary relationships within a single species. This approach might reveal instances of rapid evolution through epigenetic genetic assimilation that broader studies might miss. Imagine constructing a detailed family tree of a specific lizard population inhabiting different microhabitats within a larger island. This could reveal rapid epigenetic adaptations to these specific environments through genetic assimilation within the lizard lineage.

The Intriguing Link to Phenotypic Plasticity

The article explores the fascinating connection between genetic assimilation and phenotypic plasticity. Phenotypic plasticity refers to an organism's ability to express different phenotypes (physical characteristics) in response to environmental changes. It is caused by epigenetics. Interestingly, the same molecular mechanisms that govern phenotypic plasticity can also be instrumental in genetic assimilation.

The authors highlight a scenario where an organism exhibits a plastic response to a new environment, eventually leading to genetic assimilation. For example, imagine a desert frog that develops longer legs during a drought to travel greater distances in search of water. 

Cyclorana alboguttata legs change Rapidly due to epigenetics 

Over generations, these longer legs could become genetically fixed in the population through genetic assimilation, even in periods of normal rainfall. This suggests that studying phenotypic plasticity could offer valuable insights into the potential for rapid evolutionary change through genetic assimilation.

Macroevolutionary Implications and a More Unified View

The concept of genetic assimilation has significant implications for our understanding of macroevolution, the large-scale evolutionary changes that lead to the emergence of new species and higher-level groups. Traditionally, macroevolution is viewed as a slower process compared to microevolution (changes within a population). However, if genetic assimilation can indeed occur rapidly, it suggests that macroevolutionary events might not always be readily apparent through conventional methods. This challenges the traditional distinction between micro and macroevolution, suggesting a more continuous spectrum of evolutionary change. Imagine a population of beetles that undergoes rapid wing modification through genetic assimilation in response to a new food source on a recently emerged island. 

This could be a stepping stone towards the eventual speciation of the beetle population.

Future Directions: Unveiling the Mechanisms

The article concludes by outlining potential avenues for future research. It emphasizes the need for empirical studies that directly test the role of genetic assimilation in natural populations. Researchers could track populations over multiple generations in controlled environments to see it happening.