Charles Darwin, embryology, evolution and skeletal plasticity

Abstract

Summary Darwin provided us with the theory of evolutionary change through natural selection. Just as important to the science of biology was Darwin’s recognition that all organisms could be classified and were related to one another because they arose from a single common universal ancestor – what we know as the universal tree of life (UtoL). All the features of the skeletal biology of fish therefore can be explained, both in an evolutionary framework (ultimate causation) and in the framework of development, growth and physiology (proximate causation). Neither approach is complete without the other. I will outline the elements of Darwin’s theories on evolution and classification and, as importantly, discuss what was missing from Darwin’s theories. An important class of evidence for evolution used by Darwin came from embryology, both comparative embryology and the existence of vestiges and atavisms. After discussing this evidence I examine some fundamental features of skeletal development and evolution These include: the presence of four skeletal systems in all vertebrates; the existence of two skeletons, one based on cartilage, the other on bone and dentine; the modular nature of skeletal development and evolution; and the plasticity of the skeleton in response to either genetic or environmental changes.