Opinion
Functional evo-devo

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Functional factors such as optimal design and adaptive value have been the central concern of evolutionary biology since the advent of the New Synthesis. By contrast, evolutionary developmental biology (evo-devo) has concentrated primarily on structural factors such as the ways in which body parts can be built. These different emphases have stood in the way of an integrated understanding of the role of development in evolution. Here, we try to bridge this gap by outlining the relevance of functional factors in evo-devo. We use modularity and the view of development as a flexible evolutionary system to outline a unified perspective that includes both structural and functional aspects.

Section snippets

Development as a factor in evolution

Whereas development has long been recognized as being important in evolution, its role as an evolutionary factor has only begun to be investigated relatively recently with the study of heterochrony [1] and developmental quantitative genetics [2]. The rise of evolutionary developmental biology (evo-devo) as a biological discipline has brought about several changes in perspective 3, 4. In addition to a new focus on the developmental mechanisms that generate new variation, the discovery of the

Structural and functional factors in evolution

The debate about the relative importance of intrinsic structural factors and external adaptation in biological evolution has a long history 6, 7. By the mid-20th century, the neo-darwinian New Synthesis had established adaptation as the central theme of evolutionary biology, such that the primary research emphasis was on the external factors that shaped organisms through natural selection. The discovery of ample genetic variation in natural populations suggested that the raw material for

Modularity

Biological systems consist of parts that are recognizable because they are integrated internally and are relatively distinct from other such parts 22, 23. In general, the concept of modularity refers to this property of integration within, and relative autonomy among, the parts or modules. Modularity is studied most often in a structural context, where it refers to the spatial arrangement of physical parts at different organizational levels from molecules to entire organisms. However,

Organisms as flexible functional systems

A common theme that has emerged from analyses in evo-devo and other areas of evolutionary biology is that organisms are flexible systems. If the surroundings of an organism change, its developmental systems provide the ability to adapt to achieve and maintain some function. This can be adaptation in either the physiological or evolutionary sense, and encompasses timescales from almost instantaneous physiological responses through reaction norms on an ecological timescale (the lifecycle of an

The way ahead for functional evo-devo

Combining structuralist and functionalist perspectives will facilitate a fuller understanding of evolutionary processes. To date, evo-devo has taken a mostly structuralist approach, whereas Neo-Darwinian evolutionary biology has taken the functionalist viewpoint. A full understanding of evolution requires the use of the entire conceptual space (see Box 1), and a fusion of functional aspects with evo-devo is therefore to be welcomed.

We have outlined two subjects, modularity and flexibility, in

Acknowledgements

We thank M. Gibbs, P. Goodwyn, N. Navarro, J. Patterson, and three anonymous referees for discussion and comments on the manuscript. Financial support was provided by the European Commission, Marie Curie Intra-European Fellowships (MEIF–CT–2003–502052 and MEIF–CT–2003–502168).

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