The evolution of development

Exposure of chick embryos to certain teratogens can induce beak shape variation. This variation resembles that observed in nature, which evolved by natural selection and other processes. These observations indicate that internal factors have an important role in evolution necessitate alternative explanations for the developmental changes involved in such abrupt transitions of form.

In this context, scientists on the EU-funded 'Internalist vs externalist evolutionary biology: do we need a new synthesis?' (NEWSYN) project set out to study how developmental processes determine evolution experimentally.

They used beak development in the chick embryo as a model to analyse the transformations of the face in valproic acid-treated embryos. Morphometric analysis revealed that changes in face budding early in development precede the formation of a curved beak later on.

Work on the evolution of the skull shape in other bird species revealed that similar evolutionary patterns are seen in distantly related species with dissimilar lifestyles. This again suggested that the cause of their origination was not functional demand but rather the process of skull development.

Taken together, the NEWSYN experiments suggested that genes alone do not induce a particular phenotype. Rather they act indirectly to mobilise certain physical processes that produce a special characteristic. Evidence that evolution is driven by complex intrinsic changes and not just natural selection contributes to current debates concerning evolutionary theory.