Evolutionary Progress: Conceptual Issues

Perhaps no idea has proven more controversial within evolutionary biology than the idea that evolution manifests progress. To some biologists evidence of progress in the history of life has seemed undeniable. From utterly simple beginnings have come organisms of astounding complexity and sophistication. But to others the hazy notion of evolutionary progress appears distinctly unscientific inasmuch as it is thought to require subjective value judgements that have no place in a science based squarely on empirical facts. Debates over evolutionary progress can be substantially, albeit not entirely, resolved by examining some of the assumptions underlying such debates and by attending more carefully to the definition of key concepts such as ‘direction’ and ‘improvement’. Doing so suggests that acceptance of a moderate form of evolutionary progress can accommodate evidence from the history of life while satisfying standards of scientific objectivity.