We just finished the first session of the book “Origins of Evolutionary Innovations” by A. Wagner, on Chapter 1.
Click on “Continue Reading” to see a resume of this chapter.
What is an evolutionary innovation?
The title of this book is “The Origins of Evolutionary Innovations”. However, what is a Evolutionary Innovation? As a broad definition, an evolutionary innovation is any new trait that introduces something “novel” compared to before. For example, the discover of photosynthesis has been an evolutionary innovation, or the multicellularity has been a revolutionary thing when it appeared. The first chapter lists some nice examples of evolutionary innovations.
Nevertheless, to simplify, we can think that the concepts explained in the first chapters can be applied to any novel phenotype that has never appeared before in evolution. In fact, any phenotype has been an evolutionary innovation when it appeared for the first time. So, in a certain sense, the first chapters of the book describe how new phenotypes can be found, and how a population can explore all the possible genotypes, to find a novel phenotype.
Definition of Genotype and Phenotype
In this book, the author uses different definitions of “genotype” and “phenotype”, depending to the system analyzed. For example, if I want to study how metabolic networks evolve, I can define the genotype as the set of reactions catalyzed by an organism. Or, if I want to study glycosylation, the genotype can be just the list of glycosylation reactions that an organism can catalyze, and the phenotype can be whether the cell expresses glycosylation or not.
Since in our group we are all evolutionary biologists, this fact caused some sensation. It seems too speculative: if I am free to choose which definition of “Genotype” to use and when, I can keep changing that definition until I have found the answers that I like. If I am not satisfied with the results obtained after defining the genotype as the set of reactions expressed in an organism, I can change the definition until I find something interesting. Fortunately, I think that this is just a confusion related to the fact that we have only read the first chapter.. the other chapters clarify the issue well, as they provide nice examples of which definitions of Genotype and Phenotype to take.
Genotype Space and Genotype Network
Most of the people who attended the session were not system biologists, so I dedicated much time to explain what a “Genotype Network” is. A genotype network (also known as Neutral Network in some literature) is the set of all possible genotypes that have the same phenotype. Some definition can also be found in [1]. The concept of Genotype network is a tool that can be used to study how much genetic variability can exist in a population, without changes to the phenotype. If you want to follow the rest of the book club, make sure you have understood the concepts of genotype space and genotype networks before reading the other chapters.
1. Samal A, Matias Rodrigues JF, Jost J, Martin OC, & Wagner A (2010). Genotype networks in metabolic reaction spaces. BMC systems biology, 4 PMID: 20302636