Heikki Helanterä, Department of Biological and Environmental Sciences, University of Helsinki, POB 65, FI-00014, Finland
Tobias Uller, Department of Zoology, The Tinbergen Building, South Parks Road, Oxford, OX1 3PS, UK
Email: heikki.helantera@helsinki.fi
Received 7 October 2009; Accepted 18 November 2009
The presence of various mechanisms of non-genetic inheritance is one of the main problems for current evolutionary theory according to several critics. Sufficient empirical and conceptual reasons exist to take this claim seriously, but there is little consensus on the implications of multiple inheritance systems for evolutionary processes. Here we use the Price Equation as a starting point for a discussion of the differences between four recently proposed categories of inheritance systems; genetic, epigenetic, behavioral and symbolic. Specifically, we address how the components of the Price Equation encompass different non-genetic systems of inheritance in an attempt to clarify how the different systems are conceptually related. We conclude that the four classes of inheritance systems do not form distinct clusters with respect to their effect on the rate and direction of phenotypic change from one generation to the next in the absence or presence of selection. Instead, our analyses suggest that different inheritance systems can share features that are conceptually very similar, but that their implications for adaptive evolution nevertheless differ substantially as a result of differences in their ability to couple selection and inheritance.
We should not expect a single, universal model for ... all the dimensions of heredity and evolution
— E. Jablonka & M.J. Lamb (2005, 378)
This expanded Price Equation provides an exact description of total evolutionary change under all conditions, and for all systems of inheritance and selection
— S. Frank (1997, 1712)
Despite the statement by Jablonka and Lamb quoted above, evolutionary theorists tend to agree with Frank that there is a unifying mathematical formulation of evolutionary change, known as the Price Equation or Price Theorem (Frank 1995, 1997; Price 1970, 1972; Rice 2004). This equation has been instrumental for the development of evolutionary theory, in particular with respect to kin and multi-level selection (Frank 1998; Gardner 2008; Okasha 2006). The power of the Price Equation is that it does not make any assumptions regarding the kind of entities that evolve or the mechanisms of inheritance. Consequently, the Price Equation could provide a framework for comparing evolution under different types of inheritance mechanisms, and thereby quantify the implications of non-genetic inheritance for evolutionary theory. In this paper, we explore to what extent the Price Equation can help us conceptualize differences between inheritance systems and illustrate their effects on the rate and direction of phenotypic change.
— E. Jablonka & M.J. Lamb (2005, 378)
This expanded Price Equation provides an exact description of total evolutionary change under all conditions, and for all systems of inheritance and selection
— S. Frank (1997, 1712)
Despite the statement by Jablonka and Lamb quoted above, evolutionary theorists tend to agree with Frank that there is a unifying mathematical formulation of evolutionary change, known as the Price Equation or Price Theorem (Frank 1995, 1997; Price 1970, 1972; Rice 2004). This equation has been instrumental for the development of evolutionary theory, in particular with respect to kin and multi-level selection (Frank 1998; Gardner 2008; Okasha 2006). The power of the Price Equation is that it does not make any assumptions regarding the kind of entities that evolve or the mechanisms of inheritance. Consequently, the Price Equation could provide a framework for comparing evolution under different types of inheritance mechanisms, and thereby quantify the implications of non-genetic inheritance for evolutionary theory. In this paper, we explore to what extent the Price Equation can help us conceptualize differences between inheritance systems and illustrate their effects on the rate and direction of phenotypic change.
+++++
