Beyond the Gene: Evolution in Four Dimensions

The concept of biological information is often equated with the genetic code, a linear sequence of DNA nucleotides that holds the blueprint for an organism. 

However, Eva Jablonka and Marion J. Lamb, and their wider body of work, challenges this simplistic, gene-centric view. They argue that "the meaning of biological information" is not solely a property of the DNA sequence itself but is a dynamic process involving interpretation and context. This broader perspective fundamentally incorporates epigenetic inheritance and, in doing so, presents a significant challenge to the long-standing "Modern Synthesis" of evolutionary biology.

The Expanded Definition of Biological Information

The traditional view, rooted in the Modern Synthesis, sees information as being exclusively encoded in DNA and passed from one generation to the next. In this model, DNA mutations are the primary source of heritable variation upon which natural selection acts. 

However, Jablonka and Lamb propose that biological information is not just a static blueprint but a multi-layered system. They distinguish between the genetic information (the DNA sequence) and its meaning, which is conferred by the cellular and environmental context. .

This "meaning" is not a simple one-to-one mapping. For example, the same gene can be expressed differently in various cell types, or at different times in an organism's life, leading to a variety of outcomes. 

This means that an organism's phenotype (its observable traits) is not just a direct consequence of its genotype but is also shaped by how that genetic information is "read" and "interpreted." The "meaning" of a genetic sequence, therefore, is not inherent to the sequence itself but is an emergent property of a complex system. They propose that this "meaning" is analogous to a language, where the "letters" (nucleotides) only acquire meaning when arranged into "words" and "sentences" (genes and regulatory regions) and "interpreted" by the cellular machinery.

The Role of Epigenetics

Epigenetics is the central pillar of this expanded view of biological information. Epigenetics refers to heritable changes in gene expression that don't involve a change to the underlying DNA sequence. These mechanisms, such as DNA methylation (the addition of methyl groups to DNA) and histone modification (chemical changes to the proteins around which DNA is wound), act as a layer of control that turns genes on or off. 

While these marks are often "reset" during reproduction, a growing body of evidence shows they can sometimes be passed down to subsequent generations.

Epigenetic modifications are particularly sensitive to environmental and developmental cues. For instance, an organism's diet, stress levels, or exposure to toxins can alter its epigenetic marks, influencing gene expression and potentially leading to a different phenotype. 

The crucial point is that these changes, unlike random DNA mutations, are often directed responses to the environment. This introduces a new, non-random source of heritable variation. The inheritance of these epigenetic "memories" provides a mechanism for rapid adaptation to environmental changes without waiting for slow, random DNA mutations to arise and be selected for.

Challenging the Modern Synthesis

The Modern Synthesis, or neo-Darwinism, is a framework that emerged in the mid-20th century, uniting Darwinian evolution with Mendelian genetics. Its core tenets are:

• Genetic-centrism: All significant heritable variation is due to random gene mutations.

• Gradualism: Evolution is a slow, gradual process driven by the accumulation of these small mutations.

• Separation of Germline and Soma: Acquired characteristics (somatic changes) cannot be passed to the next generation (germline).

Epigenetics directly challenges these principles.

First, epigenetics undermines genetic-centrism by proposing a non-genetic source of heritable variation. While DNA still provides the information, epigenetic marks provide another, often more responsive, layer of inheritance. This means that a population can evolve and adapt not only through changes in gene frequency but also through the transmission of different epigenetic states.

Second, the speed and directionality of epigenetic changes contradict gradualism. Environmentally induced epigenetic modifications can occur rapidly and in a non-random manner, offering a much faster route to adaptation than random genetic mutations. This provides a potential mechanism for sudden, significant phenotypic shifts, a phenomenon known as "soft inheritance" or Lamarckian inheritance, which was largely dismissed by the Modern Synthesis.

Finally, and most directly, epigenetic inheritance breaks the strict germline-soma barrier. The fact that an acquired epigenetic change in a parent, perhaps due to a nutritional stressor, can be transmitted to their offspring directly contradicts the long-held dogma that the experiences of an organism during its lifetime cannot be inherited. This is a profound conceptual shift, moving away from a solely "bottom-up" model (DNA to organism) to a more dynamic, "top-down" model where environmental and developmental factors can influence the heritable information passed to the next generation.

In conclusion, Jablonka and Lamb's work, and the broader field of epigenetics, compel us to reconsider the very nature of biological information. It's not just the static code in our DNA but a complex, multi-layered system that includes the interpretive machinery of the cell and its history of environmental interactions. By providing a plausible mechanism for the inheritance of acquired traits, epigenetics offers a new dimension to evolutionary theory, suggesting that evolution may be a more dynamic and responsive process than previously thought, and thus necessitates an expansion of the Modern Synthesis.

YouTube of Eva Jablanka a pioneer in Epigenetics