What maintains genetic variation in natural populations? A commentary on 'The maintenance of genetic variability by mutation in a polygenic character with linked loci' by Russell Lande.

The ' Chicago School' of quantitative genetics that dominated much of evolutionary thinking in the later part of the twentieth century had its genesis at Harvard in the early 1970s. It was during this time as a graduate student in Richard Lewontin's laboratory that Russ Lande began a series of papers that would end up shaping much of the way we think about the evolution of complex traits. Lande began his graduate career with an interest in theoretical ecology but was soon motivated to translate G. G. Simpson's ideas about large-scale patterns in evolution into the formalism of population genetics developed by Sewall Wright. The merging of these approaches found their nexus in quantitative genetics, which allowed Lande to precisely formulate equations for evolutionary change in a way that made it possible to challenge his theoretical results with empirical data. In two parallel sets of papers, Lande laid out the theory of the response to selection and the maintenance of genetic variation for both single traits (Lande, 1976 a, b) and for suites of correlated characters (Lande, 1979, 1980, 1984), with the former forming the core of his disser-tation work. Together with his and Steve Arnold's work on the analysis of selection (Lande & Arnold, 1983), this theory provides a coherent system for understanding the evolution of traits whose patterns of variance and covariance are stable enough that the precise genetic details underlying this variation can essentially be ignored. The conditions under which this kind of abstraction is possible is part of the focus of Lande's seminal paper in Genetical Research published in 1976 (Lande, 1976a). Lande (1976 a) is concerned with one of the central questions in evolutionary genetics : How is genetic variation maintained within natural populations ? Lande notes that, prior to his work, mutation was thought to be insufficient to explain the high levels of genetic variation seen for many traits, yet most of the common models used to explain the maintenance of genetic variation under selection, such as overdominance or heterozygote advantage, lacked empirical support. However, the seemingly limited role for mutation might have been caused by the fact that computational difficulties had previously made it difficult to study the influence of many loci acting simultaneously. One of Lande's major contributions here was therefore developing a system for tracking the contributions of many, potentially linked, loci to the maintenance of genetic variation. To pull this …