Canalization of Development and the Inheritance of Acquired Characters: Beyond "Lamarck vs. Darwin"

Note Canals (canalization) on the Waddington diagram with differentiation of same genotype

The debate between the inheritance of acquired characters and solely genetic evolution has long haunted the halls of biology. On one side, Jean-Baptiste Lamarck proposed that traits acquired through use or disuse could be passed onto offspring, paving the way for adaptation and development. On the other, Charles Darwin's theory of natural selection championed mutations and their subsequent filtering via survival of the fittest. The tension between these two schools of thought, often reduced to "Lamarck vs. Darwin," overlooks the fascinating nuances that C.H. Waddington, the father of epigenetics, introduced his concept of canalization of development.

Waddington, in his 1942 paper "Canalization of Development and the Inheritance of Acquired Characters," argued that the dichotomy between Lamarckism and Darwinism was a false one. He proposed a middle ground, suggesting that development itself plays a crucial role in shaping phenotypic outcomes. He envisioned development as a landscape with valleys (stable phenotypes) and peaks (unstable phenotypes) above. 

Environmental factors could nudge an organism closer to a particular valley, influencing its development without directly altering its genes. This "canalization" of the developmental process biases future generations towards the same phenotype, even if not through directly inherited traits.

If we are deprived of  hypothesis of the inheritance of the effects of use and disuse (Lamarck), we seem thrown back on an exclusive reliance on the natural selection of merely chance mutations. Waddington argues that relying solely on random mutations and natural selection presents an incomplete picture. Environmental influences, acting through development, could potentially guide these mutations, directing them towards adaptive outcomes more efficiently than pure randomness allows.

Dismissing Lamarckism entirely would be shortsighted. Waddington says, "It is doubtful, however, whether even the most statistically minded geneticists are entirely satisfied that nothing more is involved than the sorting out of random mutations by the natural selective filter." He wrote this in the journal Nature the very year the Modern Synthesis was proposed by Huxley. Waddington continues, “Even ardent geneticists acknowledge that our understanding of evolution is incomplete.”

Epigenetics, for example, demonstrates how environmental factors can alter gene expression without changing the underlying DNA sequence as per neo darwinism. This suggests a potential avenue for acquired traits to influence future generations, albeit subtly and not directly.

Waddington's canalization offers a framework that reconciles these seemingly disparate views. The environment can nudge development towards certain trajectories, while mutations provide the raw material for variation. This interplay between environment, development, and epigenetics creates a dynamic system that can explain phenotypic change without resorting to strictly strictly Darwinian mechanisms.

“Beyond the theoretical, canalization” has profound implications for understanding adaptation and evolution. It suggests that phenotypic plasticity, an organism's ability to express different phenotypes in different environments, may play a more significant role in adaptation than previously thought. Additionally, it opens up avenues for exploring how epigenetic changes, triggered by environmental cues, can potentially have long-lasting impacts on populations, blurring the lines between inherited and acquired characteristics.

However, challenges remain. Quantifying the relative contributions of canalization, epigenetics, and other factors to phenotypic change is a complex task. Additionally, disentangling the effects of development from pure genetic variation can be challenging. Despite these challenges, Waddington's concept of canalization remains a valuable bridge between traditional schools of thought, pushing us to appreciate the intricate interplay between genes, environment, and development in shaping the evolutionary process.

In conclusion, the debate between Lamarckism and Darwinism is best understood as a spectrum, not a binary issue. Waddington's canalization theory, by emphasizing the role of development, offers a richer framework for understanding evolution. It shows how environment, genetic variation, and developmental pathways interact to produce the diverse tapestry of life on Earth. As we continue to unravel the mysteries of evolution, recognizing the interplay between these forces will be crucial for painting a more accurate and nuanced picture of how life changes and adapts over time.

Snippets

(1942)

The battle, which raged for so long between the theories of evolution supported by geneticists on one hand and by naturalists on the other, has in recent years gone strongly in favor of the former (Modern Synthesis).

Few biologists now doubt that genetical investigation has revealed at any rate the most important categories of hereditary variation.

The classical 'naturalist' theory-the inheritance of acquired characters-has been very generally relegated to the background because, in the forms in which it has been put forward, it has required a type of hereditary variation for the existence of which there was no adequate evidence.

The long popularity of the theory was based, not on any positive evidence for it, but on its usefulness in accounting for some of the most striking of the results of evolution

Naturalists cannot fail to be continually and deeply impressed by the adaptation of an organism to its surroundings and of the parts of the organism to each other.

These adaptive characters are inherited and some explanation of this must be provided.

If we are deprived of the hypothesis of the inheritance of the effects of use and disuse, we seem thrown back on an exclusive reliance on the natural selection of merely chance mutations

It is doubtful, however, whether even the most statistically minded geneticists are entirely satisfied that nothing more is involved than the sorting out of random mutations by the natural selective filter.

It is the purpose of this short communication to suggest that recent views on the nature of the developmental process make it easier to understand how the genotypes of evolving organisms can respond to the environment in a more coordinated fashion.