Laurent LOISON Evolving canalization by stabilizing selection : history of a conceptual problem
invité par Amaury LAMBERT - EEB Seminar Series
12h
Le séminaire de Laurent LOISON (CNRS, SPHERE) aura lieu dans la salle Favard, IBENS 46 rue d’Ulm 75005 Paris
Canalization is the property of a developmental system of resisting certain ranges of environmental or genetic perturbations. This concept emerged at the interface of genetics and causal embryology during the 1940s and 1950s, mostly thanks to Waddington’s and Schmalhausen’s work. Since the end of the 1990s, the issue of the evolution of canalization has become a topic of interest in population genetics and quantitative genetics. In such a theoretical framework, the difficulty is not to explain the evolution of environmental canalization, but to understand under which conditions genetic canalization can evolve. For this, most of the models involve stabilizing selection and assume that the standard view, since the 1950s, is that favoring intermediate phenotypes is supposed to produce genetic canalization.
This is not what history tells us. Such an account conflates two different concepts (canalizing selection and stabilizing selection) and two historical paths (the one of Waddington and the one of quantitative genetics). In my talk, I will return to the genesis of the concept of stabilizing selection (as defined by Kenneth Mather) in the context of quantitative genetics of the 1940s and 1950s, in order to show that this form of selection was defined according to the measurable characters of the individuals selected. I will contrast this account of stabilizing selection with what Waddington termed canalizing selection. This time, this form of selection was defined according to the effects it may be expected to produce (developmental canalization). Already in the 1950s, several experimental programs and mathematical models showed that stabilizing selection could not, in most cases, evolve canalization. This was the reason why Waddington embarked on a final series of experiments, around 1960, to show that under appropriate selective pressures, canalization could indeed evolve.
In my view, the confusion surrounding the term stabilizing selection has never been satisfactorily resolved since, which has contributed to making the crucial issue of the selective evolution of genetic canalization difficult