Waddington's Canalization challenges NeoDarwinism

"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." - Conrad Waddington, father of Epigenetics, Letter to Nature journal the year the Modern Synthesis  was released in '42


Conrad Hal Waddington (1905-1975) was a British developmental biologist and geneticist who introduced the concept of canalization and epigenetics to evolutionary biology. Canalization is a process by which development is buffered against genetic and environmental perturbations, resulting in a more predictable and stable outcome. Waddington used the analogy of a ball rolling down a valley to describe canalization. The ball is the developing organism, and the valley is the developmental pathway. The ball is most likely to end up at the bottom of the valley, regardless of where it starts or what obstacles it encounters along the way. This is because the sides of the valley are steep and prevent the ball from straying too far.

Similarly, canalized developmental pathways are highly resistant to perturbation. This is because they are buffered by a variety of factors, including:

  • Redundancy: Many different genes and developmental processes can contribute to the same phenotype. This means that if one gene or process is disrupted, others can compensate.

  • Feedback loops: Feedback loops can help to keep the developmental process on track, even if there are perturbations. For example, if a gene product is produced in excess, it may feedback to inhibit the production of more of that gene product.

  • Robustness of developmental networks: Developmental networks are complex systems of interacting genes and gene products. These networks are often robust to perturbation because they have many alternative pathways that can lead to the same end result.

Neo-Darwinism is the modern synthesis of Darwin's theory of evolution by natural selection and Mendel's laws of inheritance. It is the waining paradigm in evolutionary biology, and it holds that evolution is driven by the random mutation and differential survival of genes.

Waddington's concept of canalization challenges neo-Darwinism in several ways. First, it suggests that development is not as plastic as neo-Darwinism assumes. Neo-Darwinism posits that any genetic or environmental change can potentially lead to any phenotypic change. However, canalization shows that development is constrained by a variety of factors, including the epigenetic landscape and the interactions between different genes.

Second, canalization suggests that evolution is not as random as neo-Darwinism assumes. Neo-Darwinism posits that new traits arise through random mutations, and that their survival depends on whether they are beneficial or harmful under the prevailing environmental conditions. However, canalization shows that development is canalized around certain traits, making them more likely to survive and evolve.

Third, canalization suggests that evolution is not as gradual as neo-Darwinism assumes. Neo-Darwinism posits that evolution is a gradual process, with new traits arising through the accumulation of small mutations. However, canalization shows that development can be punctuated by sudden changes, as new traits become canalized and replace old traits.

Here are some specific examples of how canalization challenges neo-Darwinism:

  • Canalization can lead to the evolution of new traits that are not necessarily adaptive. For example, canalization can lead to the evolution of extreme traits, such as the peacock's tail. While such traits may not be adaptive in terms of survival, they can be sexually selected.

  • Canalization can lead to the evolution of traits that are not the result of natural selection. For example, canalization can lead to the evolution of developmental biases, which are predispositions to develop certain traits over others. Developmental biases can be caused by a variety of factors, including genetic drift and epigenetic inheritance.

  • Canalization can constrain the direction of evolution. For example, canalization can make it difficult for populations to adapt to new environmental conditions. This is because canalization buffers development against change, making it difficult for new traits to arise.

Overall, canalization is a complex phenomenon that challenges the basic assumptions of neo-Darwinism. It suggests that evolution is a more complex and nuanced process than neo-Darwinism originally suggested.

In recent years, there has been a renewed interest in the concept of canalization in evolutionary biology. This is due in part to the development of new tools and techniques, such as genomics and epigenetics, which have allowed scientists to study canalization in more detail. Canalization is an important concept in evolutionary biology because it helps to explain how populations can maintain their stability in the face of change. It also helps to explain how complex traits, such as the human brain, can evolve.

As a result of this research, we are now beginning to understand how canalization works and how it shapes the course of evolution.

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