Theories, laws, and models in evo‐devo

Abstract

Evolutionary developmental biology (evo‐devo) is the study of the evolution of developmental mechanisms. Here, I review some of the theories, models, and laws in evo‐devo, past and present. Nineteenth‐century evo‐devo was dominated by recapitulation theory and archetypes. It also gave us germ layer theory, the vertebral theory of the skull, floral organs as modified leaves, and the “inverted invertebrate” theory, among others. Newer theories and models include the frameshift theory, the genetic toolkit for development, the ABC model of flower development, the developmental hourglass, the zootype, Urbilateria, and the hox code. Some of these new theories show the influence of archetypes and recapitulation. Interestingly, recent studies support the old “primordial leaf,” “inverted invertebrate,” and “segmented head” theories. Furthermore, von Baer's first three laws may now need to be rehabilitated, and the hourglass model modified, in view of what Abzhanov has pointed out about the maternal‐zygotic transition. There are many supposed “laws” of evo‐devo but I argue that these are merely generalizations about trends in particular lineages. I argue that the “body plan” is an archetype, and is often used in such a way that it lacks any scientific meaning. Looking to the future, one challenge for evo‐devo will be to develop new theories and models to accommodate the wealth of new data from high‐throughput sequencing, including single‐cell sequencing. One step in this direction is the use of sophisticated in silico analyses, as in the “transcriptomic hourglass” models.

Expression Pattern of nos1 in the Developing Nervous System of Ray-Finned Fish

“…Comparative analyses among species that diverged millions of years ago is complex due to difficulties in comparing developmental stages between species using character homologies [40]. To make progress, we first employed an empirical staging generalization based on anatomical studies of the three species [30,33,34] because they lack a dedicated comparative characterization at molecular level for specific anatomical and CNS markers.…”

Homeostasis and evolution in relation to regeneration and repair

“…The term ‘canalization’ explains the developmental process as a ball descending in a canalized slope through a dimensional landscape referred to as an ‘epigenetic landscape’ (Waddington, 1957). The concept of epigenetics, which consists of chemical modifications in DNA, RNA or associated proteins that modulate the genome and gene expression, without changes in the DNA sequence, is in line with the new view of the evolutionary process being linked to developmental aspects driving the concept of evo‐devo and the epigenetic changes may last for decades or centuries because they may be inherited by several generations (Richardson, 2022) (Fig. 2).…”

A Transcriptomic Hourglass In Brown Algae

“…A recurring pattern of evolutionary conservation and variation across developmental stages during the life cycle of multicellular organisms was already observed by 19 th century comparative embryologists, who noticed the striking morphological similarity between embryos (von Baer 1828; Müller 1864; Haeckel 1866; His 1875). This observation was more recently revisited at the molecular level, where the morphological pattern of evolutionary conservation and variation is supported by an analogous pattern at the transcriptomic level (Drost et al 2017; Yanai 2018; Richardson 2022). Two models have been proposed to explain how conserved developmental processes accommodate evolutionary change: the early conservation model and the developmental hourglass model (and hybrids between both models).…”