For Darwin, comparative embryology was important evidence in support of the evolution of descendants from a common ancestor. In 1874, the German biologist Ernst Haeckel followed Darwin’s line of thinking with the notion that ancestral developmental processes are repeated during embryonic development, and are a record of evolutionary ancestry … ‘Ontogeny (development) recapitulates phylogeny (evolutionary history)’ … the biogenetic law that dominated evolutionary thinking in the late 19th century.
Often misinterpreted as referring to the recapitulation of adult forms rather than the forms of embryo, Walter Garstang at Leeds University, highlighted the problems of recapitulation theory in 1921, by pointing out that an adult cannot evolve directly into another adult. According to Garstang, embryonic development represents the stages of ancestors to whatever point it was in ontogeny when divergence into new forms occurred. In effect ‘Ontogeny does not recapitulate phylogeny – it drives it’. He realised that the larval stages of adult forms of many animal taxa were, according to Henson, precociously hatched embryos. Subject to Darwinian selection, larvae are potentially the nodes for major evolutionary innovation as the result of selection of larval characteristics consequently affecting adult morphology/physiology in subsequent generations.
Today, investigating the gene interactions controlling development and how these have changed through time resulting in the evolution of new taxa is now possible using the techniques of molecular genetics. Arkhat Abzhanov at Imperial College, UK et al have unravelled the intricacies of the genetic interactions controlling beak development in Darwin’s finches deepening our understanding of how new finch species/sub-species have evolved from a common ancestor arriving on the islands from South America about two million years ago.
Evolutionary-developmental biology (evo-devo) highlights how the interactions between genes might affect the micro- and macro-evolution of lineages (eg Darwin’s finches, larval forms). Today, the emerging discipline reframes the arguments of earlier evolutionary thinking, adding molecular biology to our understanding of how developmental processes influence evolution. The sessions explore a synthesis of these ideas to reassess the nature of evolution in process.
Learning outcomes
- an ability to integrate the abundant evidence from work in developmental biology and molecular genetics that increases understanding of the processes of micro- and macro-evolution;
- an appreciation of how the discovery and understanding of DNA have contributed to current evolutionary thinking;
- an understanding that phylogenetically the genetic regulation of development is highly conserved, constraining the basic body plan of metazoa to a set of components in common (not “… endless forms …”) see Charles Darwin, On the Origin of Species.
