Complexity vs. Evolovability: The Role of Pleiotropy in Evolution

Source: Wagner et al. (2008). Pleiotropic scaling of gene effects and the 'cost of complexity'. Nature 452: 470-472.

There is a intuitive notion among the biologists which indicates that complexity decreases evolvability mostly due to the pleiotropic effects. The bottom line is that a mutation in a complex organism results in more drastic changes (both in quantity and quality). The authors of this paper challenge this point of view through studying the quantitative trait loci in a set of inbred mice. Their studied traits comprise a set of skeletal variables and phenotypes. The authors show that while there is a positive correlation between the magnitude of the effects and the number of traits affected (N), N is a very small number compared to what is generally thought. When we talk about the cost of complexity, we think that each mutation can potentially affect all the phenotypes through direct or indirect effects. However, evolution can control this through enforcing modularity. In a modular system, mutations in each subset has little effects on the system as whole. In other words, robustness and modularity decrease the cost of complexity.