Table 1.

Core assumptions of the MS and the EES—after Laland et al. [1].

	modern synthesis	extended evolutionary synthesis
causality	natural selection is the pre-eminent cause of evolution, responsible for sorting variation on the basis of adaptive fitness; operates as an asymmetrical, unidirectional process in which organisms are shaped by selection to match features in the environment	causation is a reciprocal process in which organisms shape and are shaped by selective developmental environments; phenotypic changes and acquired characteristics may lead rather than invariably follow genetic change
directionality	variation arises through random genetic mutations with no directionality	variation arises through a combination of genetic and constructive processes; biases in phenotypic variation provide directionality
targets of selection	targets of selection are genes and alleles of genes; evolution consists of changes in gene frequencies	targets of selection may be alleles, genes, organisms or groups of organisms; evolution consists of change on any of these levels
inheritance	genetic inheritance is the only inheritance system; only genetically encoded traits can be inherited	multiple systems shape transgenerational inheritance, both internal to the organism (genetic, epigenetic, maternal) and external (ecological, social learning, cultural); acquired traits may be inherited
tempo and pace of change	evolution proceeds at a gradual pace made up of micro-evolutionary processes shaped primarily by selection, but also drift, mutation and gene flow	evolution proceeds at an uneven pace with periods of stasis punctuated by periods of rapid macro-evolutionary change